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Doctoral Thesis
Maize production in living mulches in a humid temperate climate
Author(s): Garibay Kuri, Salvador Vladimir
Publication Date: 1996
Permanent Link: https://doi.org/10.3929/ethz-a-001705042
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ETH Library
13. Dez. 193S
Diss. ETHNo. 11 655
MAIZE PRODUCTION IN LIVING MULCHES IN A HUMID
TEMPERATE CLIMATE
A dissertation submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY
ZURICH
for the degree of
Doctor of Natural Sciences
presented by
SALVADOR VLADIMIR GARIBAY KURI
Dipl. Ing. Agr.
University of Guadalajara (Mexico)
born December 14, 1962
in Michoacan (Mexico)
accepted on the recommendation of
Prof. Dr. P. Stamp, examiner
Dr. H.U. Amnion, co-examiner
PD Dr. B. Feil, co-examiner
Zurich, 1996
CONTENTS
SUMMARY
Zusammenfassung
1 GENERAL INTRODUCTION
2 MATERIAL AND METHODS
2.1 Experimental site and climatic conditions
2.2 Maize cropping systems
2.3 Maize and cover crop management
2.4 Fertilization
2.5 Plant sampling
2.6 Plant traits
2.7 Plant analyses
2.8 SPAD readings
2.9 Nmin concentration in the soil
2.10 Experimental design and statistical analysis
3 QUANTITY AND QUALITY OF MAIZE YIELD
3.1 Introduction
3.2 Results
3.2.1 Dry matter and N yields of maize
3.2.2 Yield components
3.2.3 Forage quality of maize
3.2.4 Total yields of the cropping systems
3.3 Discussion and conclusions
3.3.1 Maize silage yield and N yield
3.3.2 Dead grass mulch and living clover mulch systems
4 CROP GROWTH AND DEVELOPMENT
4.1 Introduction
4.2 Results
4.2.1 Dry matter and N accumulation of maize
4.2.2 Whole plant N concentration and nitrate concentration of
4.2.3 Green leaf area
4.2.4 Prediction of yield-related maize traits
4.2.5 Dry matter and N accumulation of ryegrass 57
4.2.6 Concentration of N and nitrate of ryegrass 59
4.2.7 Competition between ryegrass and maize 60
4.3 Discussion and conclusions 62
4.3.1 Nitrogen status during maize development 62
4.3.2 Maize and ryegrass competition 65
4.3.3 Leaf area 65
5 SPAD READINGS 67
5.1 Introduction 67
5.2 Results 68
5.2.1 SPAD readings 68
5.2.2 Relationship between SPAD values and other maize traits 68
5.2.3 Prediction of maize silage yield and N yield 72
5.3 Discussion and conclusions 77
5.3.1 Determination of plant N status 77
5.3.2 SPAD readings and leaf thickness 78
5.3.3 Cropping systems and SPAD readings 79
6 Nmin CONCENTRATION IN THE SOIL 80
6.1 Introduction 80
6.2 Results 81
6.2.1 Nmin content of the soil before maize sowing 81
6.2.2 Concentration and spatial distribution of Nmin during the growing
season of maize 84
6.2.3 Nmin concentration one month after maize harvest 97
6.3 Discussion and conclusions 99
6.3.1 Cover crop effects on Nmin content before maize sowing 99
6.3.2 Effect of the mulch seeding systems on the Nmin concentration 101
6.3.3 Effect of N placement and tillage 102
7 GENERAL CONCLUSIONS 105
REFERENCES 107
AcknowledgementsCurriculum Vitae
List of abbreviations
cc conventional cropping
DGM dead grass mulch
LCM living clover mulch
LCM/Chem living clover mulch, chemically suppressed
LCM/Mech living clover mulch, mechanically suppressed
LGM living grass mulch
LGM/Chem living grass mulch, chemically killed
LGM/Mech living grass mulch, mechanically regulated
ANOVA analysis of variance
CGR crop growth rates
DM dry matter
DMA dry matter accumulation
DDMY digestible dry matter yield
DMY dry matter yield
GDD growing degree days
IVOMD in vitro digestible organic matter concentration
LAI leaf area index
LNC leaf nitrogen concentration
LSD least significant differences
NA nitrogen accumulation
NC nitrogen concentration
N03C nitrate concentration
OMD organic matter digestibility
PDMA whole plant dry matter accumulation
PNA whole plant nitrogen accumulation
PNAR whole plant nitrogen accumulation rate
PNC whole plant nitrogen concentration
PNO3C whole plant nitrate concentration
SLW whole canopy specific leaf weight
RCGR relative crop growth rates
RPNA relative whole plant nitrogen accumulation
RPNAR relative whole plant nitrogen accumulation rate
RPNC relative whole plant nitrogen concentration
1
SUMMARY
Growing maize in living mulches in conjunction with reduced tillage may
alleviate or even eliminate the environmental problems associated with conventional
maize cropping methods. According to the literature, living mulches may provide the
following benefits: (i) reduced nitrate leaching hazard during the cool season, (ii)
reduced runoff of nutrients and agrochemicals, (iii) reduced soil erosion, (iv) less
structural damage by wheel traffic, (v) fewer herbicides, (vi) prevention of her¬
bicide-resistant weed populations, (vii) enhanced earth worm biomass, and (viii) reduced
infestation of maize with insects and diseases. However, living mulches and the main
crop often compete for growth factors such as N and water. In the present study, dry
matter and N yields as well as number of quality components (dry matter content,
digestibility, concentrations of N and a number of minerals) of silage maize (Zea mays
L.) in living or dead mulches of ryegrass (Lolium multiflorum Lam.) and white clover
(Trifolium repens L.) were investigated. Furthermore, the accumulation of dry matter and
N of maize as well as the seasonal patterns of some indicators of the N status of maize
(whole plant concentrations of N and nitrate and leaf greenness) were monitored.
Moreover, the temporal changes in the quantity of Nmin in the soil and its spatial
distribution were studied. The conventional maize cropping system was the control. In
addition, a maize cropping system in which the maize was planted into killed ryegrass
stands was tested. Field experiments were conducted in the midlands of Switzerland near
Zurich in 1990/91, 1991/92, and 1992/93 on a fertile sandy loam under high precipita¬
tion (about 1,000 mm per year). The maize was sown with a one-pass strip seeder tillage
system into an autumn-ploughed, bare soil (= conventional cropping; CC), living (=
living grass mulch; LGM) and dead (= glyphosate-killed dead grass mulch; DGM)
Italian ryegrass, and living white clover (= living clover mulch; LCM). The living
mulches were mechanically (= LGM/Mech and LCM/Mech) stunted, chemically killed
(LGM/Chem), or chemically stunted (LCM/Chem). Depending on the year and
cropping system, two to three N regimes were used. The N regimes were NO (= no
addition of fertilizer N), NllO (= 110 kg N ha'1; N fertilizer plus soil Nmin to 90 cm
depth at sowing), N180 (= 180 kg N ha'1; as Nl 10 plus 70 kg ha"1 N fertilizer at the 4th
leaf stage of maize), and N250 (= 250 kg N ha'1; as Nl 10 plus 70 ha'1 kg N fertilizer
at the 4th and the 6th leaf stages). Unless otherwise stated N fertilizer was applied to
the maize rows.
Maize and cropping system yields
LGM systems: The LGM systems were tested during three cropping seasons (1990/91
to 1992/93) under two levels of N supply (NllO, N250). NO was used in 1991/92 and
2
1992/93. CC maize produced higher dry matter and N yields than did LGM maize, even
though additional fertilizer N (on average 56 kg N ha"1) was applied to the LGM plots
to offset the low Nmin content of the soil at sowing. The LGM/Chem system was
superior to the LGM/Mech system in terms of dry matter and N yields. The LGM
systems were more responsive to N fertilization than was the CC system, indicating that
N is more growth-limiting in the LGM systems than in the CC system. The total
digestible dry matter yield of the LGM systems (grass cutting in spring plus silage
maize) was similar or even higher than that of CC maize. It is desirable, however, to
investigate the long-term yield stability of continuous LGM systems. The LGM systems
showed a poorer N balance than the CC system. Uptake of N by the ryegrass and
immobilization of N in decaying ryegrass residues may have contributed to this. The
conclusion may be drawn that LGM systems for maize production have to be optimized,
the aim being to increase the availability of N to the maize. As compared to broadcast
applications, placement of N fertilizer in the maize rows increased the dry matter yield
of maize under LGM/Mech by almost 20% (averaged across N110, N180, and N250).
Thus, in living mulch systems, banding of N is an integral part ofN fertilizer managem¬
ent. Maize produced under LGM/Mech tended to be less digestible (concentration of in
vitro digestible organic matter) than maize grown under LGM/Chem and CC. With
N110, maize in the LGM systems reached silage maturity later and had a lower harvest
index (= cob dry weight/total shoot dry weight) than CC maize. Averaged across the
years and N levels, however, silage maturity was reached at the same time. Whole plant
N concentration of silage maize was highest under CC and lowest under the LGM/Mech
system, irrespective of the level of N supply. With Nl 10, whole plant concentrations of
P and Mg were higher for LGM maize than for CC maize; increasing the N supply to
N250 eliminated the differences among the cropping systems. There were no significant
variations in the concentrations of Ca and K.
DGM and LCM systems: The DGM system was tested during two cropping periods
(1990/91 to 1991/92) under Nl 10 and N250. Maize dry matter and N yields were similar
to those under CC. However, these yields were reached with additional N fertilization
at sowing (on average 54 kg N ha"1). The LCM systems were tested in one cropping
season (1992/93) under two N levels (NO, N110); maize dry matter and N yields were
higher than those under the LGM systems with both NO and N110. With N110,
LCM/Chem was superior to LCM/Mech and almost equal to the CC system. It must be
taken into account, however, that the LCM systems received additional N fertilizer (50
kg N ha"1) in order to compensate for the low level of Nmin in the soil immediately
before maize planting.
3
Growth and N status of maize
The maize was harvested at five stages of development (3rd, 6th, 9th leaf stages;
pollen shedding; silage maturity) for the determination of shoot dry matter, shoot N
content, and whole plant concentrations of N and nitrate. Leaf greenness was assessed
weekly on the uppermost fully expanded leaf with a SPAD-502 chlorophyll meter. With
NO, LGM maize showed lower whole plant concentrations of nitrate and N than CC
maize already from the 3rd leaf stage onwards; crop growth rate and N accumulation
rate ofLGM maize were relatively low throughout the growing season. With Nl 10, too,
whole plant concentrations of nitrate were higher for CC maize than for LGM maize
from the 3rd leaf stage onwards, although more fertilizer N was invested into the LGM
systems to compensate for the low Nmin content of the soil at seeding. The whole plant
N concentration, SPAD readings, N accumulation rate, crop growth rate, and green leaf
area were higher for CC maize than for LGM maize from the 6th leaf stage onwards.
The differences between the cropping systems were less pronounced under high N
supply (N250). Under LGM/Chem, herbicide applications reduced the competition of the
Italian ryegrass and, thereby, enhanced crop growth rate, N accumulation rates, dry
matter formation, and N content of maize as compared to LGM/Mech maize. With both
NO and N110, LCM systems improved the dry matter and N accumulation of maize
relative to the LGM systems; whole plant N concentration and leaf greenness were
higher for LCM maize than for LGM maize. It is concluded, therefore, that the use of
legumes as cover crops may help to improve the performance of living mulch systems.
Killing the grass before maize cropping is another possibility of reducing the
competition for N and water between cover crops and the maize crop. As compared to
CC maize, DGM maize had similar or even higher whole plant concentrations of N and
nitrate. Nevertheless, final dry matter and N yields of DGM maize were not higher than
those of CC maize. The present study demonstrates that SPAD measurements enable the
early detection of N deficiency in LGM maize, especially on unfertilized plots (NO) and
plots with low N fertilization (N110). This suggests that tissue testing with the SPAD-
502 is a tool that can aid N fertilizer management. Additionally, the chlorophyll meter
detected the competition for N exerted by the live Italian ryegrass; maize under
LGM/Chem had greener leaves than maize under LGM/Mech.
Nmin in the soil
Nmin concentrations in the soil were recorded twice before maize sowing, five
times during the growing season of maize (3rd, 6th, 9th leaf stages; pollen shedding;
silage maturity), and four weeks after the final maize harvest. The sampling depth was
90 cm; three layers (0 to 30, 30 to 60, and 60 to 90 cm) were investigated. During the
growing season of maize and four weeks after the maize harvest, soil samples were
4
collected in and between the maize rows (19 and 38 cm apart). Italian ryegrass was
quite efficient in reducing the risk of nitrate leaching during the cool season; shortly
before maize planting the Nmin content of the soil (0 to 90 cm depth) averaged only 19
kg ha"1. Factors other than the N uptake by the ryegrass cover crop (on average, 52 kg
N ha"1), e.g. reduced mineralization rates and increased denitrification rates, may have
contributed to the low Nmin values. The strip tiller incorporated living grass stubble,
living clover, and dead grass residues into the soil. As indicated by the elevated Nmin
values at the 3rd leaf stage, white clover decomposed relatively fast. This was probably
due to the relatively low C/N ratio of white clover. Whole ryegrass plants presumably
have a lower C/N ratio than ryegrass stubble. For this reason and because of the
relatively long period between killing the ryegrass and maize planting, it is suggested
that N bound in the ryegrass of the DGM system became available to the maize
relatively quickly, while incorporation of the ryegrass stubble of the LGM systems may
have first caused immobilization of Nmin. Due to the N fertilizer placement in the maize
rows, the Nmin concentration decreased with increasing distance from the maize rows.
As a result of the additional banded N fertilizer application, Nmin concentrations in the
top soil (0 to 30 cm depth) in the maize row were higher on LGM plots than on CC
plots at the 3rd leaf stage. This may explain why LGM and CC maize had similar dry
matter and shoot N contents even though the LGM plots had lower Nmin concentrations
than the CC plots in the top soil between the maize rows and in the sub soil of all
sampling locations. In the LGM systems, increasing the N supply from N110 to N250
increased the N concentration in the ryegrass. The Nmin concentration in the top soil
below the maize rows declined more rapidly under the LGM systems than under CC.
This may, in part, account for the fact that the ryegrass used Nmin located in the maize
rows. Concentration of residual Nmin was low for all systems. The nitrate leaching
hazard was greater under the CC system than under LGM systems, because the CC soil
had the highest Nmin values before maize sowing, during maize development, and four
weeks after the harvest of maize. The nitrate leaching hazard of the DGM and LCM
systems was ranked midway between that of the CC and the LGM systems. As can be
deduced from the relatively poor N budget, however, the risk of nitrate leaching is only
postponed in the LGM systems.
5
Zusammenfassung
Der Anbau von Mais in lebenden Mulchen in Verbindung mit reduzierter Boden-
bearbeitung kann die mit dem herkommlichen Maisanbau assoziierten Umweltprobleme
abschwachen oder sogar eliminieren. Nach der Literatur konnen Lebendmulchsysteme
die folgenden Vorteile bieten: (1) verringerte Nitratauswaschungsgefahr insbesondere
wShrend der kiihlen Jahreszeit, (2) reduzierte Abschwemmung von Nahrstoffen und
Agrochemikalien, (3) geringere Bodenerosion, (4) weniger Strukturschaden des Bodens
durch Befahren, (5) geringerer Bedarf an Herbiziden, (6) die Entwicklung von
herbizidresistenten Unkrautpopulationen wird verhindert, (7) erhohte Regenwurm-
biomasse und (8) reduzierter Befall des Maises mit Insekten und Krankheiten. Der
lebende Mulch und die Hauptkultur konnen jedoch una Wachstumsfaktoren wie N und
Wasser konkurrieren. In dieser Arbeit wurden die Trockensubstanz-ertrage, N-Ertrage
und einige Qualitatsmerkmale (Trockenmassegehalt, Verdaulichkeit, Konzentrationen von
N und einigen Mineralstoffen) von Silomais (Zea mays L.), der in lebende Raigras-
(Lolium multiflorum Lam.) und Weisskleemulche (Trifolium repens L.) gesat wurde,
untersucht. Weiterhin wurden die Akkumulation von Trockenmasse und N beim Mais
und der saisonale Verlauf einiger Indikatoren des N-Status der Maispflanzen (Kon¬
zentrationen von N und Nitrat im Spross, Griinheit der Blatter) beobachtet. Dariiber
hinaus wurden die zeitlichen Veranderungen des Nmin-Gehaltes des Bodens und die
raumliche Verteilung des Nmin untersucht. Das konventionelle Maisanbausystem diente
als Kontrolle; daneben wurde noch ein Maisanbausystem gepriift, in dem der Mais in
einen abgetoteten Raigrasbestand gesat wurde. 1990/91, 1991/92 und 1992/93 wurden
im Schweizer Mittelland in der NShe von Zurich Feldversuche auf einem sandigem
Lehmboden bei hohen Niederschlagen (ca. 1000 mm pro Jahr) durchgefiihrt. Der Mais
wurde mit einer Streifenfrassaatmaschine in einen im Herbst gepflttgten, offenen Boden
(= konventionelles Anbausystem; PFLUG), in lebende (= lebender Grasmulch; LGM)
und mit Glyphosat abgetotete (= toter Grasmulch; TGM) Grasbestande und in lebende
Weisskleebestande (= lebender Kleemulch; LKM) gesat. Die lebenden Mulche wurde
mechanisch gehemmt (LGM/Mech und LKM/Mech), chemisch abgetotet (LGM/Chem)
oder chemisch gehemmt (LKM/Chem). Je nach Jahr und Anbausystem wurden zwei bis
drei N-Dungungsregimes gepriift. Die N-Dilngungsregimes waren NO (= kein N-Diinger
appliziert), N110 (= 110 kg N ha"1; N-Diinger plus Nmin im Boden bis 90 cm Tiefe vor
der Maissaat), N180 (= 180 kg N ha"1; wie N110 plus 70 kg ha'1 Dunger-N im 4-
Blattstadium des Maises) und N250 (wie Nl 10 plus je 70 kg ha"1 DUnger-N im 4- und
6-Blattstadium). Wenn nicht anders angegeben, wurde der N-Diinger grundsatzlich in
die Maisreihen appliziert.
6
Mais- und Anbausystemertrage
Die LGM-Systeme: Die LGM-Systeme wurden wahrend dreier Anbauperioden (1990/91
bis 1992/93) bei zwei N-Regimes (NllO, N250) gepriift. NO wurde in 1991/92 und
1992/93 gepriift. PFLUG-Mais produzierte hohere Trockenmasse- und N-Ertrage als
LGM-Mais, obwohl zusatzlicher N-Dunger (im Durchschnitt 56 kg N ha'1) verabreicht
wurde, um die niedrigen Nmin-Gehalte des Bodens bei der Maissaat auszugleichen. Das
LGM/Chem-System war dem LGM/Mech-System hinsichtlich der Trockenmasse- und
N-Ertrage iiberlegen. Die LGM-Systeme reagierten starker auf zusatzliche N-DUngung
als das PFLUG-System. Dies zeigt an, dass N mehr wachstumslimitierend fur die LGM-
Systeme wie fur das PFLUG-System ist. Der Gesamtertrage an verdaulicher Trocken¬
masse (Grasschnitt im Friihjahr plus Silomais) der LGM-Systeme und des PFLUG-
Systems waren entweder vergleichbar oder sogar hoher in den LGM-Systemen. Es ware
jedoch wiinschenswert, die Langzeit-Ertragsstabilitat von ausdauernden LGM-Systemen
zu untersuchen. Die LGM-Systeme zeigten eine schlechtere N-Bilanz als das PFLUG-
System. Die Aufnahme von N durch das Gras und N-Immobilisation durch die Zerset-
zung von Grasresten konnen dazu beigetragen haben. Es wird geschlussfolgert, dass
LGM-Systeme fur die Produktion von Mais so optimiert werden miissen, dass die
Verfugbarkeit von N fur den Mais zu verbessern ist. Im Vergleich zu breitwiirfiger N-
Dungung erhohte die Plazierung von N-Diinger in den Maisreihen den Trockenmas-
seertrag des LGM/Mech-Maises um fast 20% (Mittel von NllO, N180 und N250).
Folglich ist in Lebendmulchsystemen die N-Banddiingung ein integraler Bestandteil einer
umweltgerechten Dungungsstrategie. Der LGM/Mech-Mais war tendenziell etwas
schlechter verdaulich (Konzentration der in vitro verdaulichen Trockenmasse) als Mais,
der im PFLUG-System und im LGM/Chem-System produziert wurde. Bei NllO
erreichte LGM-Mais die Silomaisreife spSter und hatte einen geringeren Ernteindex (=
Anteil der Trockenmasse des Kolbens an der Gesamttrockenmasse des Sprosses) als der
PFLUG-Mais. Gemittelt tiber die Jahre und N-Stufen wurde die Silomaisreife jedoch
etwa zur gleichen Zeit erreicht. Unabhangig von der Hohe der N-Diingung war die N-
Konzentration im Spross bei der Schlussemte beim PFLUG-Mais am hochsten und beim
LGM/Mech-Mais am niedrigsten. Bei NllO wiesen LGM-Maispflanzen hdhere P- und
Mg-Konzentrationen als der PFLUG-Mais auf; die Erhc-hung der N-Versorgung auf
N250 eliminierte die Unterschiede zwischen den Anbausystemen. Es gab keine sig-
nifikanten Differenzen in den Konzentrationen von Ca und K im Spross.
Das TGM-System und die LKM-Systeme: Das TGM-System wurde wahrend zweier
Anbauperioden (1990/91 und 1991/92) bei NllO und N250 gepriift. Es erzeugte
Trockenmasse- und N-Ertrage, die denen des PFLUG-Systems vergleichbar waren. Diese
Ertrage wurden jedoch mit einer zusatzlichen N-Gabe bei der Maissaat (im Durchschnitt
54 kg N ha"1) erreicht. Die LKM-Systeme wurden in einer Anbauperiode (1992/93) bei
7
zwei N-Regimes (NO, Nl 10) untersucht; sie produzierten sowohl bei NO als auch bei
N110 hohere Mais-Trockenmasseertrage als die LGM-Systeme. Bei N110 war das
LKM/Chem-System dem LKM/Mech-System uberlegen und dem PFLUG-System fast
ebenburtig. Es muss jedoch beriicksichtigt werden, dass die LKM-Systeme mehr N-
Diinger als das PFLUG-System erhielten (50 kg N ha"1), urn den geringen Nmin-Gehalt
des Bodens kurz vor der Maissaat auszugleichen.
Wachstum und N-Status des Maises
Der Mais wurde an fiinf Terminen geerntet (3-, 6, 9-Blattstadium; mannliche
Bliite; Silomaisreife), um Sprosstrockenmasse, N-Masse der Sprosse und die N- und
Nitratkonzentrationen im Spross zu bestimmen. Die Griinheit der Blatter wurde
wochentlich mit dem SPAD-502-Gerat von Minolta an den obersten, voll entfalteten
Blattern gemessen. Bei NO hatte LGM-Mais bereits vom 3-Blattstadium an niedrigere
Konzentrationen von N und Nitrat im Spross; die Wachstumsrate und die N-Ak-
kumulationsrate waren wahrend der gesamten Vegetation des Maises relativ zum
PFLUG-System niedrig. Auch bei Nl 10 waren die Nitratkonzentrationen im Spross beim
PFLUG-Mais vom 3-Blattstadium an hoher als beim LGM-Mais, obwohl mehr Diinger-
N in die LGM-Systeme investiert wurde, um die niedrigen Nmin-Gehalte des Bodens
bei der Maissaat auszugleichen. Die N-Konzentration des Sprosses und die SPAD-Werte
waren vom 6-Blattstadium an honer beim PFLUG-Mais als beim Mais in den LGM-
Systemen. Ebenfalls von 6-BIattstadium an zeigte PFLUG-Mais hohere N-Akkumula-
tions- und Wachstumsraten und besass eine grossere grttne Blattflache als der LGM-
Mais. Bei hoher N-Versorgung (N250) waren die Unterschiede zwischen den Anbausys-
temen weniger ausgepragt. Die chemische Abtotung des Grases im LGM/Chem-System
reduzierte die durch das Raigras ausgeiibte Konkurrenz und erhohte daher Wachstums¬
rate, N-Akkumulationsrate, Sprosstrockenmasse und Spross-N-Masse im Vergleich zum
LGM/Mech-System. Relativ zu den LGM-Systemen zeigten die LKM-Systeme sowohl
bei NO als auch bei N110 eine hohere Akkumulation von Trockenmasse und N; die N-
Konzentration im Spross und die SPAD-Werte waren beim LKM-Mais hoher als beim
LGM-Mais. Es kann daher die Schlussfolgerung gezogen werden, dass der Einsatz von
Leguminosen als Deckfrucht dazu beitragen kann, die Leistung von Lebendmulchsys-
temen zu verbessern. Die Abtotung des Grases vor der Maissaat ist eine weitere
Moglichkeit, die Konkurrenz zwischen Mais und Deckfrucht um Wasser und N zu
verringern. Im Vergleich zum PFLUG-System waren im TGM-System die N- und
Nitratkonzentrationen im Spross des Maises ahnlich oder sogar h6her. Dennoch
produzierte das TGM-System weder einen hoheren Trockenmasseertrag noch einen
hOheren N-Ertrag als das PFLUG-System. In der vorliegenden Arbeit wurde gezeigt,
dass der N-Mangel in den LGM-Systemen schon sehr friih mit SPAD-Messungen nach-
8
gewiesen werden kann, insbesondere auf ungediingten (NO) und wenig gediingten (Nl 10)
Parzellen. Dies lasst vermuten, dass die Pflanzenanalyse mit dem SPAD-502-Ger2t zur
Bemessung der optimalen N-Diingung beitragen kann. Zudem war das Chlorophyllmess-
gerat imstande, die vom lebenden Raigras ausgeiibte Konkurrenz um N nachzuweisen;
der Mais im LGM/Chem-System hatte griinere Blatter als der Mais im LGM/Mech-
System.
Nmin im Boden
Die Nmin-Konzentration im Boden wurde an zwei Terminen vor der Maissaat,
an funf Terminen wahrend der Vegetation des Maises (3-, 6-, 9-Blattstadium; mannliche
Bliite; Silomaisreife) und vier Wochen nach der Schlussernte des Maises bestimmt. Die
Probenahmetiefe war 90 cm; es wurden drei Schichten (0 bis 30, 30 bis 60, 60 bis 90
cm) untersucht. Wahrend der Vegation des Maises und vier Wochen nach der
Schlussernte des Maises wurden die Bodenproben in den Maisreihen und zwischen den
Maisreihen (19 und 38 cm Abstand von der Maisreihe) gesammelt. Das Italienische
Raigras reduzierte die Nitratauswaschungsgefahr wahrend der kuhlen Jahreszeit recht
wirksam; kurz vor der Maissaat betrug der Nmin-Gehalt des Bodens (0 bis 90 cm Tiefe)
im Mittel der drei Anbauperioden nur 19 kg ha"'. Nicht nur die N-Aufnahme durch die
Deckfrucht, sondem auch andere Faktoren wie z.B. relativ zum PFLUG-System kleinere
N-Mineralisierungsraten und hohere Denitrifikationsraten kSnnen zu diesen niedrigen
Nmin-Werten beigetragen haben. Das Streifenfrassaatgerat arbeitete lebenden
Grasstoppel, lebenden Klee und Reste von abgetotetem Gras in den Boden ein. Wie die
im 3-Blattstadium erhohten Nmin-Werte anzeigen, zersetzte sich der Weissklee im
LKM/Mech-System relativ schnell. Dies resultierte vermutlich aus derTatsache, dass das
C/N-Verhaltnis bei Weissklee niedrig ist. Ganze Raigraspflanzen besitzen wahrscheinlich
ein niedrigeres C/N-Verhaltnis als Raigrasstoppel; dies und der relativ lange Zeitraum
bis zur Maissaat lassen vermuten, dass Teile des im Gras des TGM-Systems gebundenen
N schon friih fur den Mais verfugbar wurden, wahrend der eingearbeitete Stoppel in den
LGM-Systemen moglicherweise zunachst Nmin immobilisierte. Infolge der Plazierung
des N-Diingers in den Reihen nahm die Nmin-Konzentration mit zunehmenden Abstand
von der Reihe ab. Wegen der zusatzlichen, im Band verabreichten N-Diingung waren
im 3-Blattstadium auf den LGM-Parzellen die Nmin-Konzentrationen im Oberboden (0
bis 30 cm Tiefe) unter den Maisreihen hoher als auf den Parzellen des PFLUG-Systems.
Nmin in den LGM-Systemen war also positionell besser verfugbar als N im PFLUG-
System; dies erklart, weshalb LGM-Mais und PFLUG-Mais zu diesem Zeitpunkt noch
vergleichbare Trocken- und N-Massen hatten, obwohl auf den LGM-Parzellen die Nmin-
Konzentrationen im Oberboden zwischen den Reihen und im Unterboden aller
Probenahmeorte deutlich geringer waren. In den LGM-Systemen fiihrte die Erhohung
9
der N-Diingung von Nl 10 auf N250 zu einem Anstieg der N-Konzentration im Raigras.
Daraus kann abgeleitet werden, dass das Raigras N verwertete, das unter den Maisreihen
lokaiisiert war. Dies erklart zumindest teilweise, weshalb die Nmin-Konzentration im
Oberboden unter den Maisreihen in den LGM-Systemen schneller als im PFLUG-System
abnahm. Nach der Schlussernte waren die Rest-Nmin-Mengen in alien Systemen relativ
niedrig. Die Nitratauswaschungsgefahr war beim PFLUG-Systen grdsser als bei den
LGM-Systemen, weil der PFLUG-Boden sowohl vor der Maissaat als auch wahrend der
Vegetationsperiode des Maises und vier Wochen nach der Maissaat mehr Nmin enthielt.
Die Nitratauswaschungsgefahr im TGM-System und in den LKM-Systemen war inter-
mediar. Wie aus den relativ schlechten N-Bilanzen abgeleitet werden kann, wird in den
LGM-Systemen die Nitratauswaschungsgefahr jedoch nur verschoben.
10
1 GENERAL INTRODUCTION
Plough-tilled maize (= conventional maize cropping) is very productive in terms
of dry matter yield but contributes little to soil conservation. Some problems associated
with conventional maize production, such as soil erosion, potential contamination of the
environment with herbicides, nitrate and P would be minimal if more sustainable
production systems were developed. Oberle (1994) pointed out that, in general, the gains
in agricultural productivity since 1950 have been based to a large extent on farming
systems that depend on heavy external inputs of energy and agrochemicals. According
to Altieri (1994), the following processes must be optimized in the future to improve the
sustainability of an agroecosystem: (i) recycling of nutrients through build up of soil
organic matter and biological activity of the soil, (ii) protection and conservation of the
soil surface, e.g. through permanent cover crops and reduced tillage, (Hi) better use of
water and soil resources, (iv) use of varieties that are optimally adapted to the
environmental conditions of a cropping area and to low input conditions, and (v)
preservation of biodiversity. Until now, intercropping of maize has been restricted to
agricultural systems with low inputs of agrochemicals, typical of developing countries.
In industrial countries, however, agricultural systems are based on monocropping of
maize and advanced technology. Intercropping systems can be defined as the growing
of two or more crops simultaneously (Andrews and Kassam, 1976) in the same field.
According to this definition, cultivation of maize in living mulches may be regarded as
intercropping. Planting maize in live cover crop sods has been proposed as an alternative
to plough tilling in regions with high precipitation. Annual winter cover crops or old
meadows can be used as living mulch. The scientific investigation of living mulch
systems for maize production probably started with a study by Kurtz et al. (1946),
conducted in the USA. In Switzerland, corresponding research programs were launched
at the end of the 1980s. Switzerland is characterized by a hilly topography and a cool
humid climate (> 1,000 mm annual precipitation), i.e. conditions that favor soil erosion,
runoff of nutrients and agrochemicals, and nitrate leaching. Comprenhensive inves¬
tigations are necessary to improve the productivity of maize in living mulch systems
under such conditions.
The objectives of the present study were to
(i) compare the performance (dry matter and N yields and quality components such
as concentrations of N, P, Ca, K, Mg, and in vitro digestible organic matter) of
maize sown into living and dead mulches with that of a plough-tilled maize,
11
investigate the growth dynamics (accumulation of dry matter and N, development
of leaf area) of maize and the seasonal patterns of some indicators of the N status
of maize (whole plant concentrations of N and nitrate, leaf greenness),
describe the temporal changes in the quantity of Nmin in the soil and its spatial
distribution in various soil layers and at various sampling locations (in and
between the row) under the various cropping systems and their possible effects
on the maize crop and the environment, and
investigate the feasibility of chlorophyll readings (SPAD-502) as an indicator of
the N status of maize and as a predictor of dry matter and N yields.
12
2 MATERIAL AND METHODS
2.1 Experimental site and climatic conditions
Field experiments were conducted in 1990/91, 1991/92, and 1992/93 on a farm
near Zurich (47°30'N, 8°30'E, 424 m asl). The soil was an Eutric Cambisol
(FAO/UNESCO, 1988) with 47% sand, 35% silt, 15% clay, and 2.1% organic matter in
the top soil (0 to 30 cm). The pH (H20) was 6.5. Levels of P and K in the top soil (2.8
and 25 mg kg"1 extracted with C02-saturated water) were sufficient for optimum plant
growth. The amount of precipitation during the whole cropping period (= period from
sowing of the cover crop in August to the harvest of maize in the September of the
following year) was 1,004 mm (1990/91), 779 mm (1991/92), and 1,099 mm (1992/93)
(40-year average: 1,203 mm). During the life cycle of maize, rainfall totalled 268 mm
(1991), 303 mm (1992), and 489 mm (1993). The mean daily temperatures during the
same period were 17.8 °C (1991), 18.0 °C (1992), and 16.6 °C (1993). The daily global
radiation averaged 18.1 MJ m-2 in 1991,17.7 MJ m"2 in 1992, and 16.6 MJ m"2 in 1993.
Meteorological data were recorded at a station approximately 3 km from the experimen¬
tal field. Figs 1 and 2 and Tables 1, 2, and 3 provide additional information on weather
conditions prior to and during the cropping periods of maize. The experimental fields
had been previously planted with winter wheat (1990, 1992) or winter rye (1991).
2.2 Maize cropping systems
To vary the competition between maize and the cover crops, six maize cropping
systems were tested. The cover crops stands were sown in the late summer of the year
before planting the maize.
1. Conventional cropping (= CC): Italian ryegrass stands were broken up with a
moldboard plough in late autumn; the maize was sown into the bare soil. After
sowing, a broadcast herbicide application was carried out.
2. Living grass mulch, mechanically regulated (= LGM/Mech): maize was sown
into a living Italian ryegrass sod; the growth of grass between the maize rows
was suppressed mechanically with a mulching machine at the 1st, 3rd, and 6th
leaf stages of maize.
3. Living grass mulch, chemically killed (= LGM/Chem): maize was sown into a
living Italian ryegrass sod; the grass between the maize rows was killed by
applications of a herbicide at the 1st and 2nd leaf stages of maize.
13
4. Dead grass mulch (= DGM): maize was sown into dead Italian ryegrass mats;
the grass stands were killed chemically a few weeks before the maize was sown.
5. Living clover mulch, mechanically regulated (= LCM/Mech): maize was sown
into living white clover stands; the growth of clover between the maize rows was
controlled mechanically with a mulching machine at the 1st, 3rd, and 6th leaf
stages of maize.
6. Living clover mulch, chemically suppressed (= LCM/Chem): maize was sown
into living white clover stands; the clover between the maize rows was regulated
by a non-lethal application of a herbicide at the 1st leaf stage of maize.
The maize cropping systems CC, LGM/Chem, and LGM/Mech were evaluated in all
three cropping periods; DGM was evaluated in 1990/91 and 1991/92, and LCM/Chem
and LCM/Mech were evaluated in 1992/93.
2.3 Maize and cover crop management
Maize (Zea mays L. cv. Atlet; FAO 250) was planted at 100,000 seeds ha'1 on
23 May 1991, 12 May 1992, and 10 May 1993. Sowing was carried out by means of
the one-pass strip seeder tillage system (Amnion et al., 1990) for all six maize cropping
systems. The rows were 75 cm apart. The rototilled strips were 30 cm wide and 15 cm
deep; they were sprayed with 9 1 ha"1 Primafit A® (19% metolachlor plus 9.5% atrazine
plus 9.5% pendimethalin). The CC plots were treated with 9 1 ha"1 Primafit A®.
Italian ryegrass (Lolium multiflorum Lam. cv. Lipo) was drilled at a rate of 20
kg ha"1 on 10 August 1990, 31 August 1991, and 8 August 1992 on plots 16 m wide and
13 m long. Thirty kg N ha"1 (ammonium nitrate) was broadcast approximately one
month after sowing. The ryegrass was clipped and removed from the plots on 16
October 1990, 29 October 1991, and 12 October 1992. The CC system plots were
mouldboard ploughed on 26 October 1990, 6 December 1991, and 16 January 1993. In
the LGM/Chem and LGM/Mech treatments, the ryegrass was harvested and removed a
second time in spring (26 April 1991, 5 May 1992, and 4 May 1993). In 1991,
unfavorable weather conditions delayed the sowing of maize, and an additional cut was
made on 10 May. In the DGM treatment, the ryegrass was killed by applying 8 1 ha"1
Roundup® (41% glyphosate) on 10 April 1991 and 14 April 1992. In the LGM/Chem
treatment, the ryegrass sods between the maize rows were killed by a split application
(2 x 30 g ha"1) of the herbicide Titus® (25% rimsulfuron); 0.5 1 ha"1 of an emulsifier
(Exell®; 78% detergent and 22% ethylene glycolmonobuthylether) was added to the
spray solution. Titus® was applied on 5 June and 11 June in 1991, 29 May and 4 June
14
Table 1 Monthly precipitation [mm] dunng the three cropping periods, 40 year average
(1949/88), and deviation from the 40 year average
Cropping period 40 year Cropping periodaverage
1990/91 1991/92Month 1990/91 1991/92 1992/93 1992/93
Aug 57 8 17 3 73 7 120 0 -62 2 -102 7 -46 3
Sept 70 8 67 5 41 1 800 -9 2 -12 5 -389
Oct 114 9 22 5 123 4 66 0 48 9 -43 5 57 4
Nov 1214 97 2 1616 76 0 45 4 212 95 6
Dec 53 7 46 9 649 74 0 -20 3 -27 1 -91
Jan 46 5 15 2 23 0 710 -24 5 -55 8 -48 0
Feb 14 7 421 10 9 69 0 -54 3 -26 9 -581
March 58 1 58 0 25 7 62 0 -3 1 -4 0 -36 3
April 50 7 76 9 418 74 0 -23 3 29 -32 2
May 1013 22 4 800 90 0 113 -67 6 -100
June 173 7 1122 89 1 1130 60 7 -0 8 -23 9
July 55 5 85 9 182 4 108 0 -52 5 -221 74 4
Aug 17 3 73 7 916 1200 -102 7 -46 3 -28 4
Sept 67 5 41 1 89 3 800 -12 5 -38 9 93
Oct 22 5 123 4 89 4 660 -43 5 -57 4 23 4
WCP1 1,004 0 779 0 1,099 0 1203 0 -199 0 -424 0 -104 0
MCP2 415 3 335 3 532 4 5110 -95 7 -175 7 214
1 WCP = Whole cropping period precipitation, period from sowing of ryegrass (August) to
harvest of maize silage (September) in the following year2MCP = Maize cropping period
precipitation, period from maize planting (May) to maize harvest (September)
in 1992, and 26 May and 1 June in 1993 Titus® and Roundup® were applied with a
back sprayer pressunzed by compressed air and calibrated to deliver 400 1 ha' through
TeeJet 8015 nozzles Nozzles were placed every 40 cm apart along the boom and
operated about 40 cm above the target surface at 550 kPa pressure The ryegrass strips
in treatment LGM/Mech were regulated with a mulching machine on 4 June, 22 June,
and 9 July in 1991, on 26 May, 5 June, and 23 June in 1992, and on 26 May, 7 June,
and 21 June in 1993
White clover (Tnfohum repens L cv Milkanova) was sown on 8 August 1992
at a rate of 15 kg ha'The clover stands were cut on 12 October 1992 In treatment
LCM/Chem, 30 g ha ' Titus® and 0 5 1 ha' Exell® were sprayed on 26 May 1993 The
clover in treatment LCM/Mech was treated with a mulching machine on the same dates
as the ryegrass was regulated (dates are given above) Fig 3 shows schematically the
experimental procedures and agronomic operation dates
In all experimental years, the granulate Limax G® (6% metaldehyde) was
broadcast dunng the early stages of maize development to control field slugs (Decoceras
15
Table 2. Monthly average air temperature [°C] during the three cropping periods, 30 year
average (1931/1960), and deviation from the 30 year average.
Cropping period 30 year Cropping periodaverage
Month 1990/91 1991/92 1992/93 1990/91 1991/92 1992/93
Aug. 19.0 19.8 20.8 16.2 2.8 3.6 4.6
Sept. 13.5 16.4 14.4 12.9 0.6 3.5 1.5
Oct. 11.0 8.5 8.0 7.7 3.3 0.8 0.3Nov. 4.6 4.0 6.7 2.8 1.8 1.2 3.9
Dec. 0.4 -0.3 0.7 -0.1 0.5 -0.2 0.8Jan. 1.3 -0.9 3.3 -1.2 2.5 0.3 4.5Feb. -1.9 1.5 -0.3 0.0 -1.9 1.5 -0.3
March 6.9 5.9 4.4 3.9 3.0 2.0 0.5
April 7.7 8.4 10.7 7.7 0.0 0.7 3.0
May 10.1 14.9 14.8 12.1 -2.0 2.8 2.7
June 15.0 16.2 17.3 15.1 -0.1 1.1 2.2
July 19.9 19.2 17.3 16.9 3.0 2.3 0.4
Aug. 19.8 20.8 17.8 16.2 3.6 4.6 1.6
Sept. 16.4 14.4 13.3 12.9 3.5 1.5 0.4
Oct. 8.5 8.0 8.2 7.7 0.8 0.3 0.5
WCT' 10.3 10.6 10.7 8.8 1.5 1.8 1.9
MCT2 16.2 17.1 16.1 14.6 1.6 2.5 1.5
1WCT = mean air temperature over the cropping period; average period from sowing of
ryegrass (August) to harvest of maize silage (September) in the following year.2 MCT = mean
air temperature during the cropping period of maize; average period from maize planting (May)to maize harvest (September).
reticulatum). The European maize borer (Ostrinia nubilalis) was controlled biologically
by releasing Trichogramma tnaidis twice. In 1993, the soil insecticide Curaterr® (5%
carbofuran) was used (7 kg ha"1) to eliminate wire worms {Agriotes sp.).
2.4 Fertilization
Depending on the year and cropping system, up to three levels of N were
applied: 0 (= no addition of fertilizer N), 110 (= Nmin content in the soil from 0 to 90
cm, as measured a few days prior to sowing the maize, plus fertilizer N applied at
sowing), and 250 kg N ha"1 (= 110 kg N at sowing as described above and 70 kg ha"1
surface band placed on the maize row at botfi the 4th and 6th leaf stage of maize). The
N levels will be referred to as NO, NllO, and N250. NO was established in 1992 and
1993; the N250 treatment was not applied to plots drilled with white clover. At sowing,
40 (1991), 26 (1992), and 40 (1993) kg N ha"1 were applied to NllO and N250 by
means of the one-pass strip seeder tillage system (Table 4).
stands
ryegrass
Ital
ian
of
plou
ghin
gmoldboard
PL
spring,
in
harvest
ryegrass
H2
autumn,
in
harvest
ryegrass
HI
'),
ha
Nkg
(30
fert
iliz
atio
nN
Fryegrass,
Ital
ian
of
sowing
G(b
ars)
,precipitation
daily
of
amount
and
line
s)(dotted
temperature
air
mean
Daily
1Fi
g
010
-
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-
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40
-30fi_
-45
jlJI
-601
-75
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sowing
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Days
-105
-120
-135
-150
-165
-180
-195
-210
-225
-240
-255
-270
.1,1.flP
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1993
T
hLjl
AIIJ
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-10
-0
-10
20-
-15
-30
-45
-60
-75
1992
-130
-90
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-135
-150
-165
-180
-195
-210
-225
-240
-255
-270
-285
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1992
-90
-105
-120
-135
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-165
-180
-195
-210
-225
-240
-255
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-285
1991
January
1990
December
Hi..
liu.
Ji
November
PL
Hi
October
September
August
-10o-l
10
H20
30
maize
of
maturity
silage
MS
and
shedding
poll
enPS
leaves),
deve
loped
(ful
lystages
leaf
9th
and
6th,
3rd,
9L
and
6L,
3L,
emergence,
maize
Esowing,
maize
Sha
'),
Nkg
(70
stage
leaf
6th
and
4th
the
at
rows
the
of
fert
iliz
atio
nN
F2
Fl,
spring,
in
harvest
ryegrass
H2
(bar
s),
precipitation
daily
of
amount
and
lines)
(dotted
temperature
air
mean
Daily
2Fig
1oc
0
135
r
120
105
20
40
h
60
jlfulP
n
020
-
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MS
135
120
90
jl1,
1.,
-n
1993
sowing
maize
after
Days
75
60
45
f"
'r,
,nnn
Jlln
ltl
A
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15
Ui
105
90
75
9.
60
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H2
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15
0
10-
20-
30-i
Ho_
1-40
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020
120
I
MS
105
~i—
1992
iV
(Jin.
ni,\
40
60
rSeptember
90i
75
1991
August
60
9L
45
-k-
1
F2
SL
30
F1
3L15
-ni.
n,
ES
H2
0
10-
a
Jk
n.-a
9L
F2
HI
Fl
Jury
niuJll
lng.
„
fflfJlrj
ji
June
^20-
o
30
U
10-
20
May
-i
30
18
Table 3 Developmental stages of maize, number of days after maize sowing (DAS), mean air
temperature (Tmean, °Q, growing degree days between maize growing stages (GDDsum, base
temperature 8 °C), mean global radiation (GR, MJ m2 d '), mean precipitation (P, mm), and
precipitation between growth stages of maize (Psum, mm) during three cropping periods
Stages' DAS Tmean GDDsum GR P P^
1991
S-E 8 13 4 48 3 22 64 03 31
E-3L 26 14 2 1124 15 49 70 126 7
3L-6L 47 184 2174 2072 23 47 6
6L-9L 60 204 1613 2061 12 150
9L-PS 74 18 1 1419 17 04 29 39 9
PS-MS 120 18 9 502 6 16 70 08 35 9
S-MS 17 8 1,183 9 18 12 22 268 2
1992
S-E 6 17 5 66 6 24 11 00 00
E-3L 25 15 9 150 2 18 99 24 45 5
3L-6L 42 15 9 134 2 17 10 10 177
6L-9L 57 17 0 134 7 15 89 49 73 7
9L-PS 70 194 148 0 18 62 38 49 0
PS-MS 118 19 6 555 9 16 87 24 1175
S-MS 180 1,189 6 17 74 25 303 4
1993
S-E 7 14 9 55 1 19 54 19 15 0
E-3L 28 165 178 4 20 58 27 55 8
3L-6L 42 17 3 130 8 16 82 39 54 5
6L-9L 56 18 0 140 3 19 14 57 80 0
9L-PS 72 15 8 124 9 14 61 60 96 3
PS-MS 134 16 5 525 2 14 78 30 187 2
S-MS 166 1,154 7 16 61 36 488 8
'Stages of development S = maize sowing, E = maize emergence, 3L, 6L, and 9L = 3rd, 6th,
and 9th leaf stages (fully developed leaves), PS = pollen shedding, MS = maize silage maturity
The fertilizer was placed in the rototilled strips and incorporated into the soil Relative
to CC plots, the Nmin contents in the soil were low for plots seeded with ryegrass and
clover These plots were, therefore, treated with additional surface band applications of
N (47 kg ha]in 1991, 61 kg ha
'm 1992, and 59 kg ha
'for ryegrass and 50 kg ha
'
for clover in 1993) to reach the target N level of 110 kg N ha'Under N250, additional
N was applied on 4 and 16 July (1991), 11 and 27 June (1992), and 9 and 24 June
(1993) Nitrogen was applied as ammonium nitrate
In 1993, with one cropping system (LGM/Mech), the effects of band and
broadcast applications of N on the DM production of maize were compared in a
independent companion experiment with three levels of N supply (N110, N180, and
N250), N180 = 110 kg N at sowing as descnbed above plus 70 kg N applied at the 4th
leaf stage on 9 June According to previous soil analysis, P, K, and Mg were broadcast
19
Table 4. Nmin content of the soil just before maize sowing and N fertilization (in kg N ha"1)under N110 and N250 and different cropping systems during three cropping periods. Sidedress
N applications were carried out at the 4th, and 6th leaf stages (fully expanded leaves).
Nmin N110 N250
Croppingsystems
before maize at 4th 6th
sowing sowing2 additional3 Total leaf4 leaf" Total
1991
CC 70 40 — 40 70 70 180
LGM 23 40 47 87 70 70 227
DGM - 40 47 87 70 70 227
1992
CC 84 26 - 26 70 70 166
LGM 23 26 61 87 70 70 227
DGM - 26 61 87 70 70 227
1993
CC 69 40 — 40 70 70 180
LGM 11 40 59 99 70 70 239
LCM 20 40 50 90 - -- -
1 CC = conventional cropping; LGM = living grass mulch; DGM = dead grass mulch; LCM =
living clover mulch.2
applied with the planter at seeding.3manually spread in the rows
immediately after maize seeding.4applied to the rows.
at rates of 44,216, and 18 kg ha"1 respectively on 3 May 1991, 6 May 1992, and 6 May
1993 on all the experimental areas.
2.5 Plant sampling
Maize was harvested when 50% of the plants on CC plots had reached the 3rd,
6th, and 9th leaf stages (fully expanded leaves), at 50% pollen shedding, and at silage
maturity (= 32% DM). The final harvest took place on 20 September in 1991, 7
September in 1992, and 21 September in 1993. The maize sampling area was 3 m2, with
the exception of the last harvest date when it was 21 m2. Ten plants per plot were
harvested at silage maturity in order to assess yield components. The DM production of
ryegrass was assessed twice before the maize was sown (sampling area = 1 m2). The
first harvest was made in early spring (16 March in 1991, 17 March in 1992, and 18
March in 1993) and the second immediately before the spring cutting on 23 April in
1991, 28 April in 1992, and 4 May in 1993. During the vegetation of maize, ryegrass
was sampled on the same dates as the maize and, in addition, at the 1st leaf stage. The
sampling area was 3 m2 except at silage maturity of maize when it was 21 m2. After
silage maturity, the ryegrass was harvested again one month later. Aliquots of the
harvested maize and ryegrass samples were dried at 65 °C for 72 h.
datesoperationagronomicandproceduresexperimentaltheforSchema3Fig
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20
21
2.6 Plant traits
In 1992 and 1993, six maize plants per plot were divided into leaves, stems, ears,
and dead leaf material. The green leaf area was measured with an automatic area meter
(Li-Cor Li-300, Lincoln, Nebraska, USA) and with a conveyor-belt (Delta-T-Devices
Ltd, Burvel, Cambridge, England). The leaf blades and remaining plant material were
dried at 65 °C in a forced-air oven for 72 h.
2.7 Plant analyses
The dried plant samples were ground to pass through a 0.75 mm screen. Ground
shoot samples collected in 1991 were digested with hot sulfuric acid at 150 °C for 30
min and then at 420 °C for 90 min; the analysis for ammonium was made with an
autoanalyser (Autoanalyser n, Technicon Industrial Systems, Tarrytown, New York,
USA). Concentration of N in the ground plant samples collected in 1992 and 1993 was
assessed with a standard micro-Kjeldahl system from Tecator, Hogenas, Sweden (Kjeltec
Auto 1030 Analyser). For the determination of nitrate, 50 mg plant material was
incubated with 0.5 ml of 80% ethanol for 10 min at 60 °C. After adding 5 ml H20
bidest, samples were placed in a shaking-bath at 60 °C for 50 min. The tubes were
centrifuged at 3000 rpm for 10 min; the supernatant was analysed for nitrate with an
autoanalyser (Alliance Instruments Evolution II, Nanterre, France). Five grams of plant
material were dry ashed at 550 °C and analysed for P by a phosphate-molybdate-
vanadate method. The concentrations of K, Ca, and Mg were assessed by atomic
absorption spectometry (AAS). The in vitro digestible organic matter concentration
(IVOMD) in the DM of maize samples was determined according to Tilley and Terry
(1963); the digestible organic matter concentration (OMD) in the ryegrass samples was
obtained with a near infrared reflectance monochromator (NIRSystems 6500, Pacific
Scientific, Silver Spring, MD) according to Schubiger (1994).
2.8 SPAD readings
Relative chlorophyll measurements were carried out with a chlorophyll meter
(SPAD-502, Minolta AG, Switzerland) during maize development. SPAD measurements
were taken on 10 representative plants from each of the two center rows on the
uppermost fully expanded leaf, midway between the butt and tip and between the leaf
margin and midrib.
2.9 Nmin concentration in the soil
In spring, Nmin concentrations in three soil layers (0 to 30, 30 to 60, and 60 to
90 cm) were determined on the dates when the DM of ryegrass was assessed (dates are
given above). The diameter of the auger was 3 cm. Four cores were taken from each
22
plot and layer and mixed to one sample per plot and layer. Further soil samples were
collected shortly after the various harvests of maize (dates are given above) in the same
manner; after sowing the maize, the samples were taken from three precisely defined
locations, namely in the maize row, at a distance of 19 cm from the maize row, and
exactly between the maize rows (38 cm). These sampling locations will be referred to
as locations A, B, and C. In 1991, only the locations A and C were investigated. The
samples were stored at -20 °C until analysis. The Nmin content was assessed according
to the method described by Wehrmann and Scharpf (1979) and modified by Walther
(1983): 150 g fresh soil were shaken in 600 g extraction solution (0.01 M CaCl2) for 60
min. Concentrations of NH4-N and N03-N in the filtrate were determined with a
Technicon Autoanalyser II (Technicon Industrial Systems, Tarrytown, New York, USA).
The Nmin contents in the soil were calculated, taking into account the moisture content
and the bulk density of the soil (Walther and Jaggli, 1993).
2.10 Experimental design and statistical analysis
Plots were arranged in a randomized complete block design with four replicates.
Analyses of variance were performed for all traits using the SAS Statistical Software
Package (SAS Institute, 1988). When appropriate, data from different years were
subjected to a combined ANOVA. In these cases, years were treated as random effects
(Gomez and Gomez, 1984). Treatment effects were considered to be significant at p <
0.05. Averages across years or levels of N supply are presented only when the
interactions with the cropping system were non-significant. Means were separated by
LSD (0.05) when F-tests were significant. Growing degree days (GDD) were calculated
to facilitate the comparison of the experimental years (Table 3). Growing degree days
were defined as the sum of daily mean temperatures (mean air temperature was
registered every ten minutes and averaged over the whole day). The base temperature
was 8° C, and the ceiling temperature was 30° C.
23
3 QUANTITY AND QUALITY OF MAIZE YIELD
3.1 Introduction
Numerous environmental concerns are linked to the conventional cropping of
maize, i.e. the soil is moldboard ploughed in autumn and, after being harrowed once or
twice, the maize is sown into the bare soil. Cultivation generally accelerates net
mineralization of soil organic N (Goh and Haynes, 1986). One of the drawbacks of this
tillage system is that nitrate may be leached into the groundwater during the period
when the soil is unplanted or during the growth of young maize seedlings. Additional
problems may occur in areas with hilly topography. During periods when the soil is
unprotected by crops or crop residues, heavy rainfall may cause erosion (Wilkinson et
al., 1987) and runoff. Both erosion and runoff may increase the transport of plant
nutrients such as N and P and pesticides from cropland to lakes and streams (Riiegg,
1994). Maximum amounts of atrazine in Rhine water after maize sowing suggest a
relationship between maize cropping, erosion events, and the loss of atrazine from arable
land (Egli, 1994). If animal waste that is spread over the surface of cultivated land is
not worked into the soil and is left on the surface, exposed to rain, runoff water may
become a transport medium for nutrients. Investigations by Prasuhn and Braun (1994)
revealed that approximately 50% of soluble P, i.e. biologically available P, lost from
agricultural land in the midlands of Switzerland was carried away by surface runoff. In
the same region, both erosion and runoff contributed about 30% to the total P removal
from farmland. In Switzerland, harvest of maize is often carried out when the soils are
wet (Weisskopf, 1992) which may cause soil compaction. Soil compaction reduces the
infiltration and percolation of water, thus increasing the risk of soil erosion and runoff
(Weisskopf, 1992). Another problem associated with the conventional production of
maize is the development of herbicide-resistant weed populations. Ammon (1993)
reported that, in 1977, the first triazin resistant biotype of Lamb's quarters (Cheno-
podium album) was detected for Switzerland. An ideal maize cropping system should
minimize nitrate leaching, erosion, runoff, formation of herbicide resistant weeds, and
the use of herbicides (Ammon et al., 1992). These objectives can be accomplished with
cropping systems in which maize is sown into living mulches. A living mulch is an
intercropping system which combines an annual row crop with a cover crop (Costello,
1994). The cover crop grows for at least some of the time with the main crop
(Grossman, 1993). Living mulches may provide many benefits in an agroecosystem: (i)
the nitrate leaching hazard during late autumn and winter is reduced because of
decreased N mineralization as a result of reduced tillage and the N uptake of the cover
crop in winter (Addiscot et al., 1991; Jackson et al., 1993), (ii) the plant cover intercepts
falling raindrops, thus dissipating their energy before they strike and dislodge soil
24
particles, (iii) high plant density decreases surface water flow rates, (iv) plant roots
prevent soil from being carried away by surface runoff water, (v) soil will be less
susceptible to structural damage by wheel traffic (Sturny, 1988), (vi) weed control
between the maize rows is improved (Ilnicki and Enache, 1992), and the development
of herbicide-resistant weed populations is prevented (Ammon et al., 1995c), (vii) the
herbicide load on the environment may be reduced (Ammon et al., 1995c). Research
conducted at various locations in the midlands of Switzerland showed that mulch
seeding reduced soil erosion by more than 90% during the vegetation period of maize;
the amount of runoff water was reduced by one half to two thirds (Riittimann, 1994).
Hall et al. (1991), and Riittimann (1994) reported that the amount of atrazine exported
by runoff and erosion from sloping maize fields was markedly reduced under minimum
tillage relative to the conventional maize cropping system. Under minimum tillage,
however, more atrazine was lost by percolation (Hall et al., 1991). Stauffer (1993) found
that the presence of cover crop strips between the maize rows reduced nitrate leaching
to a varying degree. Bigler et al. (1995a,b) reported a number of phytosanitary and
ecological advantages of living interrow cover crop sods. As compared to conventionally
cultivated maize, maize sown into living ryegrass stands that were mechanically
suppressed after maize emergence was infested to a lesser extent by maize smut
(Ustilago maydis), aphids (Rhopalosiphon maidis) and European corn borers (Ostrinia
nubilalis) (Bigler et al., 1995a). The earth worm (JLumbricus terrestris) biomass was
higher (JSggi et al., 1995), and the grass strips between the maize rows harbored many
predatory insects and spiders (Bigler et al., 1995b).
Most studies using living mulches were conducted in USA (Beale and Langdale,
1964; Carreker et al., 1972; Bennett et al., 1976; Elkins et al., 1979; Scott et al., 1987;
Echtenkamp and Moomaw, 1989; and Kumwenda et al., 1993). Tillage and planting
methods developed for one region have limited application elsewhere because of
differences in climate, topography, and soil properties. The lack of experience with
living mulch systems in central Europe led us to conduct a field study in the Swiss
midlands, a region which is characterized by rolling topography and a cool, humid
climate. This chapter deals with the yields of biomass and yield structure and yield
quality of maize under various cropping systems in which maize was planted into living
or killed winter cover crop stands; the conventional maize cropping system was
considered as a control treatment.
25
3.2 Results
3.2.1 Dry matter and N yields of maize
The three cropping systems which were established in all three years (CC,
LGM/Chem, LGM/Mech) will be compared. The combined ANOVA over years revealed
that the DMY and N yield were significantly affected by year, cropping system, rate of
N application, and the interactions among these factors (Table 5). Since there were
significant three-way interactions, averages across years and N levels are shown in a few
cases only. There were large year-to-year variations in silage maize yields (Fig. 4).
Lowest yields of DM occurred in 1991 when it was unusually dry from July until the
end of the growing season (Tables 1 and 3). The highest yields were obtained in 1993
due to the warm, wet weather conditions throughout the maize growing period. With
N110, DMY was consistently higher in the CC system as compared to LGM systems
(Fig. 4). Maize grown under the LGM/Mech produced by far the lowest biomass yields
in all years. Averaged across the years, LGM/Chem produced only 69% and LGM/Mech
only 47% of the DM produced under CC. On the other hand, additions of N fertilizer
(N110 to N250) caused only small increments in DMY under CC (9%) but large
increments under LGM/Chem (49%) and LGM/Mech (98%). Nevertheless, CC was still
the most successful cropping system with N250: averaged over the years, maize grown
under LGM/Chem and LGM/Mech produced only 94% and 85% of the DM that was
produced under CC. In 1991 and 1993, LGM/Chem was clearly superior to LGM/Mech,
whereas in 1992, LGM/Chem was slighdy inferior to LGM/Mech.
Under both NI10 and N250, CC produced higher N yields than maize in the
LGM systems (Fig. 5). Averaged over the years, maize grown under LGM/Chem and
LGM/Mech with N110 contained only 53% and 31% respectively of the amount of N
yield that was measured in the maize shoots under CC. With N250, the respective
percentages were much higher (85% and 77%). It is noteworthy that, at both N levels,
the relative variation among the maize cropping systems was greater for N yield than
for DMY.
In 1991 and 1992, a fourth maize cropping system in which maize was sown into
a ryegrass sod, which was killed early in spring, was included in the experiments.
Averaged across the years, the dead grass mulch system (DGM) was as productive as
the CC in terms of DMY and N yield, irrespective of the level of N supply (Figs 4 and
5). In 1993, two additional maize cropping systems, LCM/Chem and LCM/Mech with
white clover as a living mulch, were tested. Without N fertilizer (NO), variation in the
yields of DM and N was extremely large; both DMY and N yield declined in the
following order: CC > LCM/Mech > LGM/Chem > LGM/Mech (Figs 4 and 5). In this
year, a rainstorm at the 9th leaf stage caused transient maize lodging on the N-dressed
weight
dry
shoot
total
/weight
dry
cob
=index
Harvest
41993)
(199
2,only
years
experime
ntal
two
on
based
is
variance
of
Analysis
3spring
in
harvest
ryegrass
plus
Maize
2system
cropping
=CS
supply,
Nof
level
=N
year,
=Y
'si
gnif
ican
tnot
=ns
resp
ecti
vely
001
0and
01,
005
,0
=p
at
significant
***
**,
*,
ns
***
ns
ns
***
***
**
***
*
***
*
ns
ns
***
ns
ns
ns
***
***
ns
***
ns
ns
***
***
ns
***
***
**
***
***
**
***
***
***
ns
***
***
***
***
***
***
***
***
***
***
concentration
Magnesium
concentration
Calcium
concentration
Potassium
concentration
Phosphorus
concentration
Nitr
ogen
percentage
matter
Dry
index4
Harvest
dige
stib
ilit
y3vitro
In
maize
of
value
Forage
plant
per
Ears
area
unit
per
Grains
weig
ht1000-kernelmatter
dry
Grain
area
unit
per
Plants
components
Yield
yield
Nitr
ogen
yield'
matter
dry
Dige
stib
le
yield
matter
Dry
2yield
system
Cropping
yiel
dNitrogen
yield
matter
Dry
maize
of
Yield
CS
xN
xY
NxCS
YxCS
YxN
variation
of
Source
CS
Trait
LGM/Mech)
LGM/Chem,
(CC,
systems
cropping
three
and
N250),
(N110,
supply
Nof
levels
two
traits),
two
for
(except
years
expe
rime
ntal
three
on
based
is
ANOVA
The
traits.
quality
various
and
components,
yield
yiel
d,for
years
over
ANOVA
Combined
5Table
1 cc
V77A LGM/Mech
I | LGM/Chem
f55ff DGMV=\ LCM/Mech
E55S LCM/Chem
Fig. 4. Dry matter yield (DMY) of silage maize grown under various cropping systems.
Cropping systems and levels of N supply are explained in Materials and Methods. Vertical bars
represent LSD (0.05) values and are for comparisons of cropping system means within a level
of N supply.
CC plots (Nl 10 and N250). This was probably the reason why NI10 reduced the DMY
under CC as compared to NO (Fig. 4), whereas there was a slight increase in N yield
(Fig. 5). No lodging occurred with sod-planted maize. Increasing the supply of N from
NO to Nl 10 resulted in marked increments in the production of DM (Fig. 4) and N yield
(Fig. 5). Despite transient lodging, CC continued to yield more than the LCM/Mech.
There were, however, no DMY and N yield advantages over LCM/Chem (Figs 4 and
5). It is evident that maize planted into living mulches of white clover (LCM/Mech and
LCM/Chem) yielded more than maize grown between ryegrass strips (LGM/Mech and
LGM/Chem).
In 1993, a companion experiment was carried out in order to evaluate the effects
of band and broadcast N fertilizer application under LGM/Mech. Placing N in the rows
improved DMY for all levels of N supply (Fig. 6). The gains in DM, resulting from N
placement as compared to broadcast applications of N, were 15% for N110, 33% for
N180, and 9% for N250. The effect of N placement was statistically significant at the
30
251—1
'a 20
601—'
15•a
>-. 10
2
5
0
30
25—i
's 20
60.—^
15TJ
>, 10
z
5
0
CC
Y77A LGM/Mech
LGM/Chem
15553 DGM
LCM/Mech
E?^ LCM/Chem
N110 N250
Fig. 5. Nitrogen yield of silage maize grown under various cropping systems. Cropping systemsand levels of N supply are explained in Materials and Methods. Vertical bars represent LSD
(0.05) values and are for comparisons of cropping system means within a level of N supply.
p < 0.01 level. The N supply x N placement interaction was non-significant (p = 0.16).
3.2.2 Yield components
The population density of maize was determined at silage maturity. The data in
Table 6 show that the differences in DMY were slightly influenced by variation in plant
density. The CC had consistently more plants per unit ground area than did the
LGM/Mech. The cropping system effects, however, were non-significant (Table 5).
Cropping system effects on grain yield were similar to those on DMY (Fig. 4 and
Table 6). As with the DMY, the N supply x cropping system interaction was significant
(Table 5), but the year x N supply and year x N supply x cropping system interactions
were non-significant.
The cropping systems showed little variation in 1000-kernel weight under N250
(Table 6); CC produced slightly heavier grains than LGM/Mech in almost all years.
Differences between the cropping systems were much greater with N110. In all years,
1000-kernel weight was highest under CC, second highest LGM/Chem, and lowest under
29
2500
2000
'a 1500so
I 1000
a
500
o
N110 N180 N250
Fig. 6. Effects of N fertilizer placement and level of N supply on dry matter yield (DMY) of
silage maize grown under LGM/Mech.
LGM/Mech. The cropping system x N supply interaction was significant (Table 5).
Under Nl 10, LGM/Chem and, in particular, LGM/Mech produced fewer grains
per unit area than CC, whereas there were no consistent differences among the cropping
systems with N250 (Table 6). The interaction between cropping system and N input was
significant (Table 5).
With Nl 10, CC had more cobs per plant than LGM/Chem which, in turn, had
more cobs per plant than LGM/Mech (Table 6). The number of cobs was generally
higher with N250 than Nl 10; under N250, the differences between the cropping systems
almost vanished. The interaction between cropping system and N supply was significant
(Table 5).
3.23 Forage quality of maize
The in vitro digestible organic matter concentration (IVOMD) in the DM of
maize for the three main cropping systems CC, LGM/Chem, and LGM/Mech, was
measured in 1992 and 1993 (Fig. 7). Increasing the N supply from N110 to N250
improved the digestibility of DM from 70.6 to 71.8% (data not shown). Maize from CC
and LGM/Chem plots tended to be more easily digestible than maize from LGM/Mech
plots. Even though consistent across the years, the effects of N supply and cropping
system were non-significant (Table 5).
Under the Nl 10 treatment, the harvest index of maize (= cob dry weight / total
shoot dry weight), averaged over the years, was 0.54 under CC, 0.49 under LGM/Chem,
and only 0.39 under the LGM/Mech system (Fig. 8). Thus, it is assumed that the energy
concentration was somewhat higher for maize grown under CC than for maize planted
into LGM plots. In contrast, LGM systems with N250 tended to have a higher harvest
I | Broadcast
HH In row
,11
5.Table
see
For£-tests
suppressed
.me
chan
ical
lymulch,
grass
living
=LGM/Mech
kill
ed;
chem
ical
lymulc
h,grass
living
=LGM/Chem
crop
ping
;conventional
=CC
-1110
33
51
-LS
Dro0
5)0.95
3640
221
822
9.6
N250
0.78
2400
186
485
9.4
N110
levels
Nitroeen
-480
21
57
-
lsd(
005)
0.82
2540
184
523
9.4
LGM/Mech
0.86
3020
206
650
9.6
LGM/Chem
0.91
3510
220
788
9.6
CC
C
systems
Cropping
0.02
--
-0.2
LSD(
0.05
)0.96
3530
216
782
9.4
N250
xLGM/Mech
0.95
3710
220
832
9.6
N250
xLGM/Chem
0.93
3680
228
852
9.8
N250
xCC
0.02
470
23
75
-
Lsrj
(o.o
5)0.68
1540
153
264
9.3
10
NI
xLGM/Mech
0.76
2320
192
467
9.5
10
NI
xLGM/Chem
0.89
3330
212
725
9.5
CCxNllO
level
Nx
svstem
Crooning
(no)
m"2)
(no
(g)
weig
htm2)
(gm"
2)(no
plant
per
Ears
number
Grain
1000-kernel
yield
Grain
density
Plant
years.
three
across
means
are
Data
N250).
and
10
(NI
supp
lyN
of
levels
two
and
LGM/Mech)
and
LGM/Chem,
(CC,
systems
crop
ping
three
under
maize
silage
of
components
Yield
6.Table
31
725
£ 720
Q
>71500
— CC
_
1773 LGM/Mech
I | LGM/Chem
710 -
P£ 705
700
Fig. 7. In vitro digestible organic matter concentration (F/OMD) in the dry matter of silagemaize. Cropping systems are described in Materials and Methods. Values are means of two years
(1992, 1993) and two levels of N supply.
index than the CC system (CC: 0.59; LGM/Chem: 0.61; LGM/Mech 0.63). The cropping
system x N supply interaction (Table 5) and the cropping system effects within the
levels of N supply were non-significant; this must, in part, be attributed to the fact that
the harvest index was determined on only 10 plants per plot.
With N250, the percentage of DM at silage maturity tended to be higher for
LGM systems than for CC (Fig. 9). With N110, however, LGM/Mech had the lowest
values. The interaction between cropping system and N supply was significant, but the
effects of N supply and cropping system were non-significant (Table 5).
80
~70
B 60o
£
1 50
ac
WM cc
_
V77X LGM/Mech
I I LGM/Chem
40 -
30
Fig. 8. Harvest index of silage maize grown under various cropping systems. The harvest index
is defined as cob dry weight / total shoot dry weight. The values are means of three years.
Cropping systems and levels of N supply are explained in Materials and Methods.
5Table
see
£-tests
For
supp
ress
edme
chan
ical
lymulch,
grass
living
=LGM/Mech
kill
ed,
chem
ical
lymulch,
grass
living
=LGM/Chem
cropping,
conventional
=CC
1013
-—
022
0070
0
112
0229
019
1176
01085
126
0225
0131
226
0792
0
005
0—
—023
0075
0
128
0224
023
1225
0852
0
116
0214
023
10215
900
0
0114
244
029
1162
01065
toLO
053
0
0112
223
016
1177
01053
109
0216
011
1189
01044
0116
248
029
1162
0158
1
010
0-
-021
0128
0
145
0225
031
1273
0655
0
123
0211
0135
243
0755
0
112
0240
0128
162
0971
0
LSD(
oos)
N250
N110
levels
Nitrogen
LGM/Mech
LGM/Chem
CC
systems
Cropping
N250
xLGM/Mech
N250
xLGM/Chem
N250
xCC
LSD(
005)
10
NI
xLGM/Mech
10
xNl
LGM/Chem
CCxNllO
level
Nx
system
Cropping
Magnesium
Calcium
Potassium
Phosphorus
Nitrogen
years
three
across
means
are
Data
N250)
and
10
(NI
supply
Nof
levels
two
and
LGM/Mech)
and
LGM/Chem,
(CC,
systems
cropping
three
under
maize
sila
gein
Mg
and
Ca,
K,
P,N,
of
cent)
per
(in
concentration
Plant
7.Table
33
JO
- CC
34 - V77X LGM/Mechr^)_,
-
" | | LGM/Chem K-
* 32 -
an
"
a 30 ^H -
s .
u
g 28 -
a. ^Bvv -
26 -
?4JP n "
N110 N250
Fig. 9. Percent dry matter of silage maize grown under various cropping systems. Values are
means of three years. Cropping systems and levels of N supply are explained in Materials and
Methods.
Although the nutritive value of maize forage is primarily associated with fiber
content and digestibility, concentrations of protein and minerals in whole plants also
influence maize forage quality. Maize grown on CC plots exhibited the highest
concentrations of N, irrespective of year and N supply (Tables 5 and 7). The cropping
systems responded differently to increased supplies of N; the increments in N
concentration were most pronounced for cropping systems in which ryegrass was used
as living mulch. With NI10, CC, cropping system resulting in the highest yields, showed
the lowest concentrations of P and Mg, and LGM/Mech, which produced the lowest
yields, exhibited the highest concentration of those minerals (Table 7). Increasing the
level of N supply from Nl 10 to N250 reduced the concentrations of P, K, and Mg for
all cropping systems. With N250, the cropping systems showed only minor differences
in the concentrations of minerals. In summary, the data suggest that factors which cause
large increments in DM production, such as N fertilization and use of high-yielding
cropping methods, cause the concentration of some minerals (P, K, Mg) to decline. Only
the concentration of Ca was not inversely related to the production of DM; maize in CC
had the highest concentration of Ca at both levels of N supply.
3.2.4 Total yields of the cropping systems
In evaluating the economical value of LGM systems, the economical return of
spring haylage yield and pastures has to be taken into account. Averaged over 1991 to
1993, the ryegrass cutting immediately before maize sowing yielded 3.87 t ha'1 DM
(Fig. 10 a), and the average N yield was 52 kg N ha"1 (Fig. 10 b). The organic matter
of the Italian ryegrass was highly digestible (79.5%) (Fig. 10 c). In order to obtain total
34
600 100
80 -
*60
S5
40 -
20 -
lb
I
- ,1,1.1.1,1991 1992 1993
700
1991 1992 1993
Fig. 10. (a) Dry matter yield (DMY), (b) N yield, and (c) the digestible organic matter
concentration (OMD) in the dry matter of ryegrass which was harvested immediately before
maize sowing. Vertical bars represent LSD (0.05) values.
yields of the cropping systems (averaged over 1992 to 1993), the digestible dry matter
yields (DDMY) of maize and Italian ryegrass were summed. Figure 11 a shows averages
across 1992 and 1993; in interpreting the data in Fig. 11 a, it must be taken into account
that there were statistically significant year x cropping system interactions with N110
(p < 0.01) and N250 (p < 0.05). With N110, LGM/Chem plots produced 93% and
LGM/Mech 76% of the digestible DM produced on the CC plots. With N250, the
respective percentages were 116 (LGM/Chem) and 113 (LGM/Mech), i.e. the LGM
systems were more productive than CC. The lack of significant differences between the
cropping systems can be traced, at least in part, to the presence of significant year x
cropping system interactions (see above). Total N yields (maize plus ryegrass) are shown
in Fig. 11 b. With N110, total N yield was greatest for the CC system; with N250,
however, the LGM/Mech and LGM/Chem systems had a slight advantage over CC. With
both levels of N supply, the year x cropping system interaction was significant at p <
0.001.
35
2000 ZJ
.
•T 20~b
"
00
" 15 - m t-
•a' I1"3 I •
-10 1 III "
3-
I I IIIS 5 "
r H r*!"
- INllOl I N250 1 "
0 L»J1 lonl
1 2 3 1 2 3
Fig. 11. (a) Total digestible dry matter yield (DDMY) and (b) total N yield (maize plus ryegrassharvest in spring) under various cropping systems. Values in (a) are means across two years
(1992 and 1993) and those in (b) are means across three years (1991,1992, 1993) respectively.1 = CC; 2 = LGM/Mech; 3 = LGM/Chem. Cropping systems and levels of N supply are
explained in Materials and Methods. Vertical bars represent LSD (0.05) values.
36
3.3 Discussion and conclusions
3.3.1 Maize silage yield and N yield
In the present study, Italian ryegrass was used as living mulch for the following
reasons: Italian ryegrass is optimal for stubble seed after winter cereals, because it grows
fast, has very good regrowth ability, is quite resistant to diseases, offers high forage
quality, is easy to combine with different forage mixtures, is strongly competitive with
weeds, and shows a high uptake of N (Nosberger and Optiz von Boberfeld, 1986).
Furthermore, sowing Italian ryegrass during late summer efficiently reduces nitrate
leaching during the autumn/winter period (Andersen and Olsen, 1993; Jackson et al.,
1993). Moreover, Italian ryegrass is well suited for the utilization of slurry (Smith et al.,
1992). For these reasons, Italian ryegrass is widely used by Swiss farmers.
In Switzerland, maize producers traditionally plough in autumn, followed by one
or more harrowings to prepare the seedbed for sowing maize. The adoption of
alternative cropping systems puts conservation-minded maize producers into a dilema:
mulch seeding systems have fewer adverse effects on the environment (e.g. less soil
erosion, runoff of herbicides, and nitrate leaching), but the CC system is very productive
both in terms of DMY and the N yield of maize; none of the evaluated mulch seeding
systems produced higher maize yields, and the most favorable maize cropping system
in terms of the environment (LGM/Mech) produced relatively low yields, especially
when it was established under low levels of N supply (Figs 4 and 5). When comparing
the cropping systems, however, the yield of the ryegrass must also be considered. If the
total digestible dry matter yield (DDMY) (maize plus ryegrass yield) is taken as a
measure, LGM/Chem was almost as productive as CC (with N110) and clearly more
productive with N250 (Fig. 11 a). The LGM/Mech showed higher yields than the CC
with N250, whereas with Nl 10, LGM/Mech had lower yields; however, the effects of
the cropping systems were non-significant at both N levels. Klocke (1989) compared
maize planted into suppressed and non-suppressed living grass mulches of smooth brome
grass (Bromus inermis Leyss.) with conventionally grown maize and grass monocultures.
He found no significant differences in DM production when the conventionally grown
maize yield plus the monocropped grass yield was compared with the total DMY from
intercropped maize/grass of an equivalent land area. Klocke (1989) concluded that direct
comparisons of intercropped maize with monocropped maize should take into account
the total yield of biomass, because the purpose of maize intercropped with a LGM is to
provide a combination of grain and forage. In the present study, the yield from the first
ryegrass cutting in late autumn was not considered, because it was the same for the CC
and LGM systems. In Swiss farming systems, however, grass is not cut in autumn,
because the soil is usually tilled and kept free of green cover after harvesting the main
37
crops. Adams et al. (1970) pointed out that, in LGM systems, considerable grazing or
hay can be obtained after the maize harvest. In fact, under LGM/Mech (with the
exception ofN250 in 1993), considerable ryegrass biomass was produced after the silage
harvest of maize (Table 11). Under continuous LGM/Mech maize, it is possible to graze
cattle on these areas in autumn after the maize harvest, and in the following spring,
grass can be harvested a few days prior to maize planting which may help to improve
the long-term profitability of LGM/Mech. Thus, the LGM/Mech system may be more
productive than traditionally tilled maize. However, it is necessary to investigate the
long-term stability of continuous LGM/Mech systems.
It must be bome in mind that additional N (on average 56 kg N ha'1) was applied
to the LGM systems in order to offset the low Nmin content of the soil immediately
prior to maize planting (Table 4). When the plants relied exclusively on soil-derived N
(NO), LGM/Chem and LGM/Mech produced extremely low DMY of maize relative to
the CC system. Only when the input of N was fairly high (N250) did biomass maize
yields of LGM/Chem and LGM/Mech approach those of CC (Fig. 4). Thus, maize
grown in a LGM of Italian ryegrass (LGM/Chem and LGM/Mech) seems to have very
high N requirements to reach maximum maize yield. It would be inappropiate from an
environmental point of view to apply high N rates in order to eliminate differences in
yield compared to CC. Instead, the LGM systems should be optimized. Not all cultivars
of a crop species respond in the same way to changes in the environment (Davis and
Woolley, 1993). Maize breeding programs should aim at developing cultivars that are
more competitive with the sod or are better adapted to the low availability of soil
resources. Plant species that compete aggressively with weeds and vigorously protect the
soil, such as Italian ryegrass, also compete strongly with the crop (Lake, 1991). Ammon
et al. (1995a) pointed out mat living mulches of old meadows with a high proportion of
white clover are less competitive with maize than grass mixtures with a high proportion
of Italian ryegrass. Butler (1986) considered the following characteristics to be desirable
for grasses for use as living mulches: low growth, fast germination and soil cover,
drought and shade tolerance, and wear-resistance (e.g turf-type perennial ryegrasses with
slow spread). Nicholson and Wien (1983) evaluated 30 grasses and 52 legumes to select
suitable groundcovers for use as living mulches in the production of sweet maize and
cabbage. They concluded that short and not very vigorous turf grasses (e.g. Poa sp. and
Festuca sp.) are the most promising cover crops.
Since N is very mobile in soil, placement of N fertilizer is not regarded as
critical for CC (Randall et al., 1985). This may be different for sod-planted maize in
combination with minimal tillage. Live grass strips form a great sink for fertilizer N,
suggesting that placement of N fertilizer in the rototilled maize rows may improve the
N supply to the maize crop. In fact, the data in Fig. 6 demonstrate that applying N
38
fertilizer to the rows is an integral part of correct N fertilizer management for maize
production in living grass mulches. Kurtz et al. (1946) pointed out that, in living mulch
systems, N applications are more effective if N fertilizer is placed into the tilled strip
instead of being broadcast. Mengel et al. (1982) reported a beneficial effect of the
subsurface application of fertilizer N for no-till maize, probably because no-till
production systems leave a layer of crop residues on the soil surface that can cause
increased immobilization of N (Rice and Smith, 1984). Minimizing the contact between
fertilizer and organic residue has been considered as a means of improving the use of
fertilizer N (Wagger and Mengel, 1988). Klocke et al. (1989) applied NH3 to the soil
at depths of 15 to 20 cm along the side of the tilled strip. In the present study, N
fertilizer applied in 1991 at the 4th and 6th leaf stages of maize stayed on the soil
surface longer due to the low precipitation after fertilization (Fig. 2). This may have
caused a positional unavailability of the N fertilizer (Figs 34 and 35). At the same time,
the ryegrass strips absorbed N from the soil, and the soil water content was probably
lower under LGM plots than under CC plots. Leaf wilting was first observed under
LGM/Mech (at about the 6th leaf stage until the end of the growing season), somewhat
later under LGM/Chem, and finally during the grain filling period under CC. All this
may have led to the observation that symptoms of N deficiency first occurred under the
LGM/Mech system, irrespective of the level of N supply (Figs 18 and 19). The
unavailability of N fertilizer and the loss of N by ammonia volatilization is reduced if
the N fertilizer is incorporated into the soil immediately after application (Murphy
1983).
Adams et al. (1970) and Carreker et al. (1972) concluded that the success of
LGM systems depends on the water status of the soil. Even though the experiments were
not designed to elucidate the effect of water supply on the silage yield under the various
maize cropping systems and rates ofN application, several points bear mentioning. First,
despite large year-to-year fluctuations in precipitation, the cropping year had only a
limited influence on the relative performance of the cropping systems (Fig. 4). The
chronological sequence in the occurrence of water deficiency symptoms mentioned
above indicates that, in 1991, water was most probably more yield-limiting for
LGM/Mech plots than for maize under CC plots. This suggestion is supported by the
fact that, with N250, the silage yield under the LGM/Mech system, expressed as a
percentage of that under CC, was lowest in 1991 (68% versus 97% in 1992 and 87%
in 1993). During the present study, precipitation during the cropping period (14 month
period from August to September) and during the maize cropping period (maize planting
to maize harvest) were below the long-term average (Table 1); only in 1993 was the
amount of precipitation during the maize cropping period normal. It is possible,
therefore, that the mulch seeding systems would perform somewhat better in long-term
39
investigations.
The data on the total N yield (Fig. 11 b) indicate a potential drawback of the
LGM/Mech and LGM/Chem systems: with N110, less N was yielded (ryegrass and
maize) under LGM systems than under CC, even though more N was applied to the
LGM plots. With N250, the situation was reversed, but the advantages of the LGM
systems over CC were smaller than the additionally applied amount of fertilizer N, i.e.
56 kg N ha"1. In other words, the LGM/Mech and LGM/Chem systems showed a poorer
N balance than CC. The following three points, however, were not considered in this
balance. First, at the harvest of maize, the ryegrass strips in the LGM/Mech system
contained appreciable amounts of N (averaged across the three years, 18 and 9 kg N ha"1
with N110 and N250 respectively). Second, after the maize harvest in the LGM/Mech
system, the recovering ryegrass swards absorbed N from the soil solution (about 10 kg
N ha"1), thus rendering it non-leachable. Third, the LGM systems were compared with
an atypical CC system which is not very common in Switzerland; the CC system does
not include a cover crop that is harvested in autumn. In the present study, the LGM
systems would perform relatively better if only the N balance of the N yield from the
ryegrass cutting in autumn was included, whereas it is not considered in the N balance
of the CC.
As compared to CC, maize grown on the LGM plots (LGM/Mech and
LGM/Chem) contained less N in the aboveground phytomass, even though the amount
of mineral N at sowing (Nmin plus N fertilizer) was similar for all cropping systems.
According to Doran (1980) and Rice and Smith (1984), there is an increased potential
for immobilization of N at the surface of no-till soils. Under LGM/Chem and
LGM/Mech, some N fertilizer and soil-derived mineral N became trapped in the
decaying ryegrass mulch or in live tissues throughout the maize cropping period, thus
rendering it unavailable to the maize plants (see chapter 4). This N may be liberated
after tillage operations which disturb and aerate the soil. The oxidization of organic
matter may result in a build up of soil nitrate which may escape from the plant-soil
system during periods when the soil is uncropped or when the N uptake capacity of the
crop is limited. When maize is planted continuously into perennial living grass mulches,
(e.g. LGM/Mech), it is unlikely that nitrate leaching will occur as long as the soil
remains unfilled. If it is necessary to plough the soil, however, large amounts of nitrate
may be released from decomposing organic matter that may become subject to leaching.
In maize - winter wheat rotations, the risk of nitrate leaching may be reduced by seeding
the winter wheat with no-till or reduced tillage methods. Thus, avoidance of tillage will
help reduce the amount of N at the risk of leaching (Christian and Ball, 1994).
40
3.3.2 Dead grass mulch and living clover mulch systems
The yields of DM and N of maize can be improved and the post-harvest nitrate
leaching hazard diminished by killing the cover crop sod a few weeks before maize
sowing. This can be achieved by the incorporation of the cover crop as green manure
or by the application of herbicides, as with the dead grass mulch system (DGM) (Figs
4 and 5). Elkins et al. (1983) investigated the effects of various living grass mulches on
the yield of maize and observed that the maize yield was 4% to 21% lower than the
yield of maize grown in grass mulch that was almost all dead (90 to 99%). Box et al.
(1980) reported similar yield differences for maize grown in living and dead grass
mulches. Moschler et al. (1967) evaluated the yields of maize sown into various killed
winter cover crops, including Italian ryegrass. These authors reported that maize yields
increased, or at least stayed the same, in comparison to conventional tillage as a result
of sod-planting. In the experiment in 1991 and 1992, maize grown underDGM produced
about the same DMY and N yield as CC (Figs 4 and 5); in contrast to the results of
Thomas et al. (1973), CC and DGM showed similar responses to increasing levels of
N supply. Hence, DGM appears to be a feasible alternative to CC. It must be borne in
mind, however, that the DGM plots received 54 kg more N ha"1 (mean of 1991 and
1992; Table 4) than the CC plots. Many other disadvantages are associated with DGM,
such as the lack of hay or haylage yield in spring, a potential delay in the sowing of
maize due to high soil moisture caused by the dead mulch cover, possible failure of the
herbicide treatment (e.g. glyphosate), and high infestation with wire worms which may
make it necessary to apply soil insecticides. Thus, the success of DGM depends on high
inputs of pesticides. Furthermore, the DGM system does not show the ecological
benefits of a full-season interrow cover crop.
This is the case, however, with LCM/Chem and LCM/Mech, two cropping
systems which use white clover as the living mulch. With a relatively low N input
(Nl 10) both systems produced fairly high DMY and N yield (Figs 4 and 5). Leguminous
living mulches may add symbiotically fixed N (Grubinger and Minotti 1990). Thus,
competition between maize and the cover crop for N should be less pronounced than
under LGM/Mech. A drawback of both LCM/Chem and LCM/Mech is that the forage
production of pure white clover stands is negligible. Ammon and Scherrer (1996)
suggested replacing white clover by the more productive red clover (Trifolium pratense
L.). Lake (1991) reported that the yield of maize is improved, when red clover was used
as living mulch instead of white clover. He attributed this to differences in root and
shoot morphology. Red clover has tap-roots and shows a more upright growth, thus
interfering to a lesser extent with the maize than does the low, spreading stoloniferus
habit of white clover. Ammon and Garibay (1995) pointed out that an early suppression
of the red clover may provide a better N availability to the maize in deep soil layers and
41
a better soil structure than is the case with white clover. Nicholson and Wien (1983)
reported that shading white clover by the maize canopy greatly reduced clover growth.
This was also observed with LCM/Mech and LCM/Chem (data not available). It seems
that a stable living mulch is difficult to achieve with legumes, except perhaps for crown
vetch (Hartwig, 1983). However, if legumes are combined with grasses, the grass may
survive until the maize harvest which may reduce the nitrate leaching hazard after the
harvest of maize.
42
4 CROP GROWTH AND DEVELOPMENT
4.1 Introduction
The use of living mulch for maize production in combination with strip tillage
may have phytosanitary and ecological advantages (Scott et al., 1987; Bigler et al.,
1995a,b). However, living cover crops may have adverse effects on the growth and
development of the main crop. Research on living mulches in maize production focused
on the effects of living mulch on the dry matter yield (Enache and Ilnicki, 1990),
possibilities of regulating the living mulch (Wilkinson et al., 1987), type of living mulch
for maize production (Ammon et al., 1994), herbicide losses due to runoff (Hall et al.,
1984), maize plant arrangement (Harper et al., 1980; Jellum and Kuo, 1990), control of
erosion (Wall et al., 1991), and weed management (Teasdale, 1993). However, there is
limited information on the development and growth of maize planted into a living
mulch. Most of the published research was conducted on clover and other legumes
which were used as living mulch (Corak et al., 1991). Therefore, field experiments were
carried out in order to determine the effects of living grass mulch on the growth and N
status of maize under conditions in Switzerland. In the following chapter, the seasonal
patterns of dry matter formation, N accumulation, and some indicators of the N status
of maize will be considered.
4.2 Results
4.2.1 Dry matter and N accumulation of maize
In Table 8, results of the ANOVA for various traits are presented. At the 3rd leaf
stage (= first sampling date) the fertilized plots (Nl 10 and N250) were supplied with the
same amount of N fertilizer. Only the effects of die cropping systems were, therefore,
considered. All N treatments were fully randomized, but data for the levels of N supply
are shown separately in the graphs to improve the clarity of the figures.
Crop growth rates (CGR) and their relative values as percentages of those under
CC (100% = mean of the levels of N supply) are depicted in Figs 12 and 13 respec¬
tively. The crop growth rate is defined as the rate of DM accumulation per unit ground
area (Warren, 1981) and was calculated using the formula CGR = A whole plant DM
accumulation / A growing degree days. In 1991 and with both N levels, maize under
LGM/Mech showed lower CGR than that under CC and LGM/Chem from the 6th leaf
stage of maize onwards. With Nl 10, differences between CC and LGM/Chem occurred
from pollen shedding until silage maturity. In 1992 with Nl 10, CC showed higher CGR
than the LGM systems from the first sampling date (3rd leaf stage) until silage maturity.
43
Table 8. Significance of the effects of CS (CC, LGM/Chem and LGM/Mech), level of N supply(N110 and N250), and the interaction between CS and level of N supply on traits of maize.
Source of variation
CS N CSxN
Trait 1991 1992 1993 1991 1992 1993 1991 1992 1993
PDMA1
3rd ns*** **
„ „ - - ~ -
6th * ***ns ns ns ns ns ns ns
9th *** *** ***ns ns
*ns ns ns
PS *** *** *** *** *** *** *ns
**
SM *** #** *** *** *** *** ** *** ***
PNA
3rd ns*** *
- « - - - -
6th *** *** ***ns
*ns ns ns ns
9th *#* *** *** ** ***ns ns ns ns
PS *** *** *** *** *** *ns
* **
SM *** *** *** *** *** *** ** *** **
CGR
3rd ns*** **
~ „ - - - -
6th * **# *ns
*ns ns ns ns
9th *** *** *** *ns
*ns ns ns
PS *** * * ** *** *ns ns ns
SM *** *** *** *** *** *** * *** ***
PNAR
3rd ns*** *
- -- - - - -
6th *** *** ***ns
** ***ns ns ns
9th *** *** *** ** *** ***ns ns ns
PS **ns ns
*** #** *** *ns ns
SM ns ns* * * ***
ns#*
ns
PNC
3rd *** ** **— — _ _ — -
6th *** *** ***ns ns
***ns
* ***
9th *** *** *** ** *** ***ns
*** ***
PS ** *** #** *** *** *** ** *** **
SM *** *** *** *** *** *** # *** *
PN03C3rd *** *** ***
.. — - - — -
6th *** *** ***ns
* ***ns ns
*
9th ** *** ***ns
*** ***ns ns
**
PS * *** **# *** *** ***ns
* ***
SM *** *** *** *** *** **+ *** **ns
13rd, 6th, and 9th = leaf stages; PS = pollen shedding; SM = silage maturity; PDMA = whole plant
DMA; PNA = whole plant NA; CGR = crop growth rate; PNAR = whole plant NA rate; PNC =
whole plant N cone; PN03C = whole plant nitrate cone. *, **, *** significant at p = 0.05, 0.01, and
0.001 respectively, ns = not significant. CS = cropping systems.
44
CC
LGM/Chem
LGM/Mech
DGM
LCM/Chem
LCM/Mech
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [ °C d ]
Fig. 12. Crop growth rates of maize (CGR) under various cropping systems. Cropping systemsand levels of N supply are explained in Materials and Methods. Vertical bars are LSD (0.05)values. Results of the ANOVA are presented in Table 8.
Under LGM/Chem and LGM/Mech, CGR was more or less the same throughout the
vegetation period. With N250, the CGR of maize under CC was superior only to that
under the LGM systems until the 9th leaf stage. In 1993 with Nl 10, differences in CGR
between the CC and LGM systems occurred from the 9th leaf stage onwards; relative
to CC, LGM/Chem showed reductions of approximately 55% and 35% until silage
maturity. Under N250, lower CGR in LGM/Mech and LGM/Chem than in CC were ob-
CC
LGM/Chem
LGM/Mech
DGM
LCM/Chem
LCM/Mech
150
T 100
eot 50
150
T 100
Oo« 50
150
" 100
°iOO* 50
III
' I I ' I I I
_1_ J i—L _1_
I I I I
' I ' I I I I 1
_l_ _1_
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°Cd]
Fig. 13. Relative crop growth (RCGR) rates of maize expressed as a percentage of that under
CC (100% = mean of the two (in 1991 and 1992) or three (in 1993) levels of N supply) under
various cropping systems. Cropping systems and levels of N supply are explained in Materials
and Methods.
served between the 6th leaf stage and pollen shedding.
Figure 14 shows the whole plant N accumulation rates (PNAR); the relative
values as percentages of those under CC (100% = mean of the levels of N supply) are
depicted in Fig. 15; whole plant N accumulation rates were computed as follows: PNAR
= A total whole plant N accumulation / A growing degree days. Under both levels of N
46
supply, all cropping systems had approximately the same PNAR at the 3rd leaf stage of
maize, except in 1992. In 1992, there was almost no rainfall for 20 days after maize
sowing (Fig. 2), suggesting that the lack of moisture in the top soil reduced the
availability of fertilizer N which was applied to the LGM plots. In the LGM systems,
this effect caused a reduction in PNAR to about 40% relative to CC. In each year and
with N110, CC showed higher PNAR than the LGM systems from the 6th leaf stage
onwards. Under CC, the PNAR peaked consistently at the 9th leaf stage of maize
development. In 1992 and 1993, the PNAR declined sharply thereafter, but in 1991 a
relatively high PNAR was maintained until pollen shedding. In this year, after a period
with almost no precipitation (4th to 9th leaf stage; Fig. 2), 40 mm rainfall was recorded
from the 9th leaf stage to pollen shedding (Table 3), i.e. the level of plant-available soil
N probably increased. The acute drop in 1993 was due to a heavy rainstorm which
caused lodging on the fertilized CC plots only. At the onset of grain filling the plants
straightened and, as a result, PNAR increased again. Differences in PNAR between
LGM/Chem and LGM/Mech were not consistent over the years. In 1993, PNAR was
higher throughout the growing season under LGM/Chem than under LGM/Mech. In
1991, however, this was true only for the first part of the growing season, and in 1992
LGM/Chem and LGM/Mech showed a similar PNAR over almost the entire vegetation
period. In 1991 and 1993, with N250, differences between CC and LGM systems
occurred as early as the second sampling date. In 1992, these differences were observed
from the first sampling until the 9th leaf stage. The higher PNAR under CC compared
to that under LGM/Mech was maintained until pollen shedding (1991) or the 9th leaf
stage (1992, 1993). Thereafter, the PNAR of maize grown on CC plots declined sharply,
and CC and LGM/Mech showed about the same PNAR during grain filling. In 1991, CC
and LGM/Chem showed similar courses of PNAR throughout the cropping period,
whereas in 1992 and 1993 the curves of LGM/Chem were similar to those of
LGM/Mech.
The CGR of maize grown on DGM plots (Figs 12 and 13) was similar to that
under the LGM systems from the 3rd to the 9th leaf stage. Thereafter, it excelled that
of the LGM systems; at pollen shedding, maize under DGM showed an even higher
CGR than under CC, independent ofN supply. Thereafter, the differences between DGM
and CC disappeared. With Nl 10, DGM reached the same levels of PNAR as CC at the
9th leaf stage (Figs 14 and 15). Under both N supplies, maize grown in DGM surpassed
the levels of PNAR for maize under the CC at pollen shedding. Maize grown in living
clover mulch systems (LCM) had a slightly lower CGR than maize grown in LGM
systems until the 6th leaf stage (Figs 12 and 13). Thereafter, the CGR in the LCM
systems increased and, during the rest of the growing season, was similar to that under
CC. The seasonal trends were similar for the PNAR (Figs 14 and 15). At the 9th leaf
LGM/Chem u
LGM/Mech 55
DGM*"
LCM/Chem
• LCM/Mech
0.06
g0.04 -
a
£
0.02
0.00
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [ °C d ]
Fig. 14. Whole plant N accumulation rates of maize (PNAR) under various cropping systems.
Cropping systems and levels of N supply are explained in Materials and Methods. Vertical bars
are LSD (0.05) values. Results of the ANOVA are presented in Table 8.
stage, at pollen shedding, but not at silage maturity, maize in the LCM systems
exceeded that of maize under CC. On unfertilized plots (NO), CGR and PNAR of maize
grown in CC plots exceeded the rates obtained in the LGM systems from the first
sampling until silage maturity (Figs 12 to 15). The LGM/Chem started to differ from
the LGM/Mech from the 9th leaf stage on.
Relative whole plant DM accumulation (RPDMA) and relative whole plant N
48
-o- CC
-a- LGM/Chem
-a— LGM/Mech
-- DGM
-r- LCM/Chem
-•— LCM/Mech
200
I
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°Cd]
Fig 15 Relative whole plant N accumulation rates (RPNAR) of maize as a percentage of that
under CC (100% = mean of the two (in 1991 and 1992) or three (in 1993) levels of N supply)under vanous cropping systems Cropping systems and levels of N supply are explained in
Materials and Methods
accumulation (RPNA), as a percentage of the CC (100% = mean of the levels of N
supply), are depicted in Figs 16 and 17 In 1991, LGM/Mech had the lowest RPDMA
and RPNA among the cropping systems from the 6th leaf stage onwards, irrespective
of the levels of N supply As already mentioned, the extremely low values under
LGM/Mech may be explained by drought-induced low N availability In 1992 with both
150
100
.NO
8& 50
-i L
49
150
100
CC
LGM/Chem
LGM/Mech
DGM
& 50
150LCM/Chem
LCM/Mech
100
a so
n i r
_i_
' I ' I I I ' I
92
I ' I i I i I
_L. _1_ _1_
-—r—<—i—i—i——r
N250
I ' I ' I ' I
I i 1 i I I
o—
_1_ J_ _1_ _1_
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°Cd]
Fig. 16. Relative whole plant DM accumulation (RPDMA), expressed as a percentage of that
under CC (100% = mean of the two (in 1991 and 1992) or three (in 1993) levels of N supply)under various maize cropping systems. Cropping systems and levels of N supply are explainedin Materials and Methods. Results of the ANOVA are presented in Table 8.
N levels, RPDMA in the DGM system was similar to the LGM systems until the 9th
leaf stage. After that, irrespective of N supply, maize grown in DGM reached a similar
RPDMA as the maize in CC. From pollen shedding onwards, differences between the
cropping systems were smaller with N250 than with Nl 10. With Nl 10, the RPNA under
DGM started to differ from that under the LGM systems at 6th leaf stage, with N250,
z
-o- CC S-D- LGM/Chem
—**- LGM/Mech
-- DGM
—r- LCM/Chem
—•— LCM/Mech
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [ °C d ]
Fig. 17. Relative whole plant N accumulation (RPNA), expressed as a percentage of that under
CC (100% = mean of the two (in 1991 and 1992) or three (in 1993) levels of N supply) under
various maize cropping systems. Cropping systems and levels of N supply are explained in
Materials and Methods. Results of the ANOVA are presented in Table 8.
at the 9th leaf stage. Maize grown on LCM plots had a lower RPDMA and RPNA than
under CC until the 6th leaf stage. Thereafter, maize in the LCM systems reached the
levels of RPDMA and RPNA of the CC. Without an N application (NO), maize in the
LGM systems had a clearly lower RPDMA and RPNA than in the CC throughout the
cycle of maize. Generally, LGM/Chem had higher RPDMA and RPNA than LGM/Mech
-o- CC
-a- LGM/Chem
^- LGM/Mech
-- DGM
-t— LCM/Chem
-•- LCM/Mech
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°Cd]
Fig. 18. Whole plant N concentrations of maize (PNC) under various cropping systems.
Cropping systems and levels of N supply are explained in Materials and Methods. Vertical bars
are LSD (0.05) values. Results of the ANOVA are presented in Table 8.
in all cropping periods and independent of N supply. Such differences between the
regulation methods were also observed under LCM systems.
4.2.2 Whole plant N and nitrate concentration of maize
In all years under Nl 10 and N250, the whole plant N concentrations (PNC) were
initially similar in all the maize production systems (Fig. 18, the relative values Fig. 19),
52
150
" 100
-o- CC RPNC—a— LGM/Chem
—a— LGM/Mech
—- DGM
-T- LCM/Chem
—*— LCM/Mech
£
50
150
100
50
-r-T—i—i i i i—[-
91 NllO
' I i I i I I
92
A --
-1-1—'—I—'—r——|—
N250
i I i 1 ' I i I
1
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°Cd]
Fig 19 Relative whole plant N concentrations of maize (RPNC) expressed as a percentage of
that under CC (100% = mean of the two (in 1991 and 1992) or three (in 1993) levels of N
supply) under various cropping systems Cropping systems and levels of N supply are explainedin Materials and Methods
whereas with NO, CC showed higher values than the LGM systems until the third
sampling date (i e 9th leaf stage) With Nl 10, the curves for all cropping periods started
to separate at the 6tii leaf stage of maize Under CC, PNC was higher throughout the
growing season than under the LGM systems Differences between LGM systems were
small, but PNC was consistently higher under LGM/Chem than under LGM/Mech With
0.9
Bh
0.3
CC
LGM/Chem 0.0
LGM/Mech 0.9
DGM
53
t——i—'—i—'—r
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [ °C d ]
Fig. 20. Whole plant nitrate concentrations (PNOjC) in maize under various cropping systems.
Cropping systems and levels of N supply are explained in Materials and Methods. Bars are LSD
(0.05) values. Results of the ANOVA are presented in Table 8.
N250 the situation was similar, but variation between the CC and LGM systems was less
pronounced. With Nl 10, the DGM system had a slightly higher PNC than CC from the
9th leaf stage until pollen shedding. Under N250, no differences were observed between
the CC and DGM system at any of the stages. The PNC in the LCM systems were not
different to that under CC until the 6th leaf stage. However, at the 9th leaf stage and
pollen shedding, PNC under the LCM systems surpassed PNC under CC. The PNC
54
under LCM/Chem was consistently higher than under LCM/Mech.
The courses of whole plant nitrate concentration (PN03C) are depicted in Fig.
20. Under both N regimes, concentrations of nitrate were highest in CC from the first
sampling date onwards. Data for the 3rd leaf stage in 1991 are not available. With
NllO, nitrate concentrations were similar for LGM/Chem and LGM/Mech throughout
the growing season. With N250, however, nitrate concentrations tended to be higher for
LGM/Chem than for LGM/Mech, especially in 1992 and 1993.
4.2.3 Green leaf area
With Nl 10, the green leaf area under CC was higher than that under the LGM
systems from the 6th (1992) and 9th leaf stage (1993) onwards (Fig. 21). With N250,
the differences between the CC and LGM systems became noticeable from the 6th leaf
stage onwards in both years. In 1992, the largest green leaf area was reached at the 9th
5000
'§ 4000
1 1
~92tr- f
i i
NllO"
i 1 1 1
N250-
a
§ 3000
"a
I
•jj 2000 -
n- -
O 1000 - / :-
/, i i 01 i i i
5000
93 1i i i
>"<\N110*
1 L 1 1
^\ N250:
a
[cm s 0\I : i^Na :g 3000 III03
-O- CC
—o- LGM/Chem
-A- LGM/Mech~
1 1 1
-
S 20005aO 1000
i i i i
300 600 900 1200 300 600 900 1200
Growing degree days [ CC d ]
Fig. 21. Development of the green leaf area of maize under various cropping systems. Cropping
systems and levels of N supply are explained in Materials and Methods. Bars are LSD (0.05)values.
55
leaf stage and in 1993 at pollen shedding. With Nl 10, the green leaf area in the LGM
systems was reduced by almost 30% during grain filling, whereas that under CC showed
a reduction of 25% (averages of 1992 and 1993). With N250, the total green leaf area
was reduced by 18, 16 and 17% in the CC, LGM/Chem and LGM/Mech systems
respectively.
4.2.4 Prediction of yield-related maize traits
Table 9. Correlations of DM yield, leaf area index, and N yield at silage maturity with various
traits during maize development.
1991
Stages of development1
Traits2 3rd 6th 9th PS SM
DMY vs
CGR -0.04 +0.31 +0.73 *** +0.84 *** +0.92 ***
PNAR -0.19 +0.70 *** +0.81 *** +0.76 *** +0.56 **
PNA -0.19 +0.69 *** +0.84 *** +0.92 *** +0.96 ***
PNC -0.57 ** +0.71 *** +0.83 *** +0.71 *** +0.67 ***
PN03C -0.27 +0.56 ** +0.63 ** +0.55 ** +0.41 *
N yield vs
CGR -0.15 +0.19 +0.64 *** +0.83 *** +0.90 ***
PNAR -0.28 +0.65 *** +0.78 *** +0.84 *** +0.63 **
PNC -0.56 ** +0.73 *** +0.84 *** +0.81 *** +0.84 ***
PNO3C -0.38 +0.63 ** +0.70 *** +0.67 *** +0.54 **
13rd, 6th, and 9th leaf stages of maize; PS = pollen shedding; SM = silage maturity.
2 DMY
= DM yield; LAI = leaf area index; CGR = crop growth rates; PNAR = whole plant N
accumulation rates; PNA = whole plant N accumulation; PNC = whole plant N concentration;
PNO3C = whole plant nitrate concentration. Correlations are based on two levels of N supply(Nl 10 and N250), three cropping systems (CC, LGM/Chem and LGM/Mech), and four replicates(= 24 cases). *, **, *** significant at p = 0.05, 0.01, and 0.001 respectively.
Dry matter yield (DMY), leaf area index (LAI), and N yield at silage maturity
(Tables 9 and 10) were positively correlated with the whole plant nitrate concentration
(PN03C) already at the 3rd leaf stage (at this sampling stage there are no differences in
the levels of N supply) in 1992 and 1993 and at the 6th leaf stage in 1991. The positive
correlation coefficients of the relationship between DMY and whole plant N con¬
centration (PNC) were generally higher than those of the relationship between DMY and
PNO3C, but they were significant only from the 6th leaf stage onwards. The DMY was
highly correlated (r > 0.8) with the PNC from the 9th and 6th leaf stages until silage
maturity in 1992 and 1993 respectively. In 1991, tight relationships were found at the
9th leaf stage only. In 1992 and 1993, tight relationships (r > 0.8) between the DMY
and the PNQ3C were found only at the 9th and 6th leaf stage. In all years, the closest
resp
ecti
vely
001
0and
01,
005,
0=
pat
sign
ific
ant
***
**,
*,ca
ses)
24
(=
repl
icat
esfour
and
LGM/Mech),
and
LGM/Chem
(CC,
systems
cropping
three
N250),
and
10
(NI
supply
Nof
levels
two
on
based
are
Correlations
concentration
nitrate
plan
twhole
=PNO3C
concentration,
Npl
ant
whole
=PNC
accumula
tion,
Nplant
whole
=PNA
rates,
accumulation
Npl
ant
whole
=PNAR
rates,
growth
crop
=CGR
inde
x,area
leaf
=LAI
yiel
d,DM
=DMY
2ma
turi
tysi
lage
=SM
shedding,
poll
en=
PS
maize,
of
stages
leaf
9th
and
6th,
3rd,
1
***
81
+0
***
76
+0
***
70
+0
***
80
+0
*51
+0
***
76
+0
***
75
+0
***
91
+0
***
63
+0
+046*
PNO3C
***
98
+0
***
96
+0
***
94
+0
***
88
+0
-007
***
97
+0
***
91
+0
***
92
+0
**
54
+0
12
+0
PNC
+090***
***
66
+0
***
89
+0
***
+077
27
-0
***
66
+0
***
73
+0
***
89
+0
**
57
+0
38
+0
PNAR
+096***
60**
+0
***
76
+0
+020
22
-0
***
94
+0
***
+074
*44
+0
**
54
+0
*39
+0
CGR
vs
yield
N
***
78
+0
***
72
+0
***
71
+0
***
77
+0
**
55
+0
***
73
+0
***
+075
***
87
+0
**
62
+0
50*
+0
PNO3C
***
87
+0
***
91
+0
***
78
+0
05
+0
***
87
+0
***
85
+0
***
86
+0
***
64
+0
05
-0
PNC
°"
***
87
+0
lh
***
86
+0
***
88
+0
***
85
+0
***
72
+0
-020
***
87
+0
***
+092
***
81
+0
**
63
+0
+028
PNA
***
68
+0
**
54
+0
***
86
+0
***
70
+0
020
34
+0
***
74
+0
***
79
+0
***
65
+0
28
+0
PNAR
***
79
+0
**
55
+0
***
69
+0
22
+0
20
-0
***
75
+0
***
74
+0
*40
+0
**
61
+0
31
+0
CGR
vs
LAI
70***
+0
***
66
+0
***
66
+0
***
84
+0
*49
+0
***
68
+0
***
+068
***
88
+0
**
61
+0
*42
+0
PN03C
90***
+0
***
91
+0
***
92
+0
***
+093
-009
***
92
+0
***
87
+0
***
91
+0
**
56
+0
12
+0
PNC
***
97
+0
***
93
+0
***
89
+0
***
79
+0
29
-0
***
98
+0
***
+092
***
83
+0
**
56
+0
*+041
PNA
***
88
+0
**
60
+0
***
88
+0
***
79
+0
29
-0
***
+066
***
71
+0
***
86
+0
**
57
+0
*+041
PNAR
***
98
+0
***
64
+0
***
82
+0
18
+0
24
-0
***
96
+0
***
76
+0
*43
+0
**
54
+0
*+043
CGR
DMYvs
SM
PS
9th
6th
3rd
SM
PS
9th
6th
3rd
Trai
ts2
development1
of
Stages
development1
of
Stages
,993
1992
development
maize
during
traits
various
with
matu
rity
sila
geat
yield
Nand
inde
x,area
leaf
yiel
d,DM
of
Correlations
10
Table
57
relationships were found first between DMY and PNAR and then between DMY and
CGR The LAI was positively correlated with the CGR at early stages of maize
development in 1992 (Table 10), but in 1993 significant correlations coefficients were
found only from the 9th leaf stage onwards In both years, significant positive
correlation coefficients were also detected for the relationship between LAI and PNC
from the 6th leaf stage onwards (Table 10) High correlations (r > 0.8) between LAI and
PNC, PNAR, and PNA were reached at the 9th leaf stage in 1992 and 1993 The N
yield and PNAR were highly correlated (r > 0 8) at pollen shedding in 1991 (Table 9),
and at the 9th leaf stage in 1992 and 1993 (Table 10) The N yield was highly correlated
with PNC and PN03C at the 9th leaf stage m 1991 and 1992, whereas in 1993 close
relationships existed even earlier, at the 6th leaf stage
4.2.5 Dry matter and N accumulation of ryegrass
Table 11 Accumulation [g m 2] of dry matter and N of the ryegrass strips under the LGM/Mech systemwhen the mechanical regulation was earned out and one month after silage maize harvest
Dry matter
LSDro05)
N accumulation
Stage'/year NO N110 N250 NO N110 N250 LSD(005)
1st leaf
1991 - 108 106 - - 165 161 -
1992 - 63 80 - - 122 168 -
1993 — 72 79 - - 2 37 2 71 -
mean2 -- 81 88 - - 175 200 --
3rd leaf
1991 68 63 - - 2 65 244 -
1992 20 25 25 - 0 54 0 87 0 98 014
1993 40 70 76 15 102 2 56 2 80 050
mean2 30 54 55 -- 0 78 2 03 2 07 --
6th leaf
1991 - 116 114 - - 3 14 3 14 -
1992 26 71 58 30 0 75 2 27 218 0 84
1993 47 81 92 27 122 2 79 3 68 096
mean2 37 89 88 - 099 2 73 300 -
ASM
1991 ~ 43 39 .. - 149 162 -
1992 - 30 32 - - 0 84 1 15 -
1993 - 23 2 9 -- 0 92 007 0 29
mean2 -- 32 24 - - 108 095 --
'1st, 3rd, and 6th = leaf stages of maize, ASM = one month after the harvest of maize silage
2 The LSD
values for the mean are for the fertilized (Nl 10 and N250) plots only for the three years (1991,1992 and
1993)
58
160
60 120
3 80
O 40 -
<Z
o
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°Cd]
Fig. 22. Dry matter accumulation (DMA) and N accumulation (NA) of ryegrass under the
LGM/Mech system from the 6th leaf stage to silage maturity, when no mechanical regulationwas carried out. The N levels are explained in Materials and Methods. Bars are LSD (0.05)values.
In all cropping periods, the DM accumulation (DMA) and N accumulation (NA)
of ryegrass were similar for the fertilized plots (NllO and N250) until the pollen
shedding of maize (Table 11 and Fig. 22). The DMA and NA of ryegrass at silage
maturity, treated with Nl 10, was clearly greater than with N250 in 1992 and 1993 (Fig.
22). In 1991, however, no depression was observed as a result of high levels of N
fertilization. Only in 1993 were the DMA and NA of ryegrass significantly greater one
month after the maize harvest (Table 11), when NllO was applied instead of N250.
Compared to fertilized plots (NllO and N250), ryegrass on non-fertilized plots (NO)
showed less DMA until the 9th leaf stage and less NA until pollen shedding (Table 11
and Fig. 22). In 1993, at silage maturity, the DMA and NA of the ryegrass on the NO
plots exceeded the DMA and NA obtained under Nl 10 and N250.
59
250
LGM/Chem
777X LGM/Mech
1991 1992 1993 1991 1992 1993
Fig. 23. Dry matter accumulation (DMA) and N accumulation (NA) of ryegrass at the 3rd leaf
stage of maize (LGM/Mech and LGM/Chem). The values for LGM/Mech are the sums of two
harvests which were conducted at the first and second mulchings, i.e. at the 1st and 3rd leaf
stage of maize. Cropping systems and levels of N supply are explained in Materials and
Methods. Bars are LSD (0.05) values.
To compare the accumulation of DM and N of ryegrass in the LGM systems
(LGM/Chem and LGM/Mech) at the 3rd leaf stage, the DMA and NA of ryegrass under
the LGM/Mech on the first and second mulching dates respectively were summed (Fig.
23). Averaged across the years, the NA of ryegrass was 1.8 g N m"2 under both LGM
systems before the first herbicide application or mulching treatment (= 1st leaf stage).
Under LGM/Chem, the NA increased to 2.6 g N m"2 until the 3rd leaf stage, even
though the herbicide treatment had already been carried out at the 1st and 2nd leaf
stages (i.e., 8 kg N ha'1 were accumulated between the 1st and 3rd leaf stage). Under
LGM/Mech, the NA average of the ryegrass at the 3rd leaf stage was 3.9 g N m"2 (i.e.,
the NA increased by 21 kg N ha"1).
4.2.6 Concentration of N and nitrate of ryegrass
The concentrations of N (NC) and nitrate (N03C) in the ryegrass in the strips
(Fig. 24) were affected by N110 and N250 as follows: in 1993, the high N fertilization
induced an increase in NC and N03C as early as the 6th leaf stage; in 1992, the NC and
N03C of ryegrass stands were already affected at the 3rd leaf stage, whereas in 1991,
the effects of N applications occurred from pollen shedding onwards. Including the
unfertilized ryegrass stands in the ANOVA of 1992 and 1993, the concentrations of N
and nitrate in the ryegrass on the NO plots was significantly different to those under
N110 and N250 throughout the growing period.
60
g 3
o
2 -
1 1
91
i i i i i
'§-1 i i i >
93
:<V-
i
i
i
i
>^
:i> ^ I"
r i1 \—
—•
• i i . i• i..
i
i i i i i i
i.i.i.
z
1 1„.
1.6
1.2*
t;
o" 0.8z09
Bo 0.4
0.0
i——i—i—i—i—r —i 1 1 r
92
" I
-v- NO-o- NllO
-*- N250
n I r
93
-i—i—r
_i L
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [ °C d ]
Fig 24 Nitrogen concentration (NC) and nitrate concentration (N03C) in ryegrass under the
LGM/Mech system TheN levels are explained in Materials and Methods Vertical bars representLSD (0 05) values and are for comparisons of N supply
4.2.7 Competition between ryegrass and maize
Under LGM/Mech, the leaf area index of maize may have played an important
role in reducing competition by ryegrass during the intercropping period. Figure 25 a
shows that the maize yield was negatively correlated (r = -0 71***) with the DMA of the
ryegrass at maize silage maturity. The DMA of Italian ryegrass also displayed a negative
relationship (r = -0.67***) with the leaf area index (LAI) of maize (Fig. 25 b), indicating
that a large canopy may suppress the DMA of the Italian ryegrass. This conclusion is
clearly corroborated by data obtained m 1993: on the N250 plots almost no ryegrass
survived up to maize silage maturity (Fig. 22).
61
40 80 120 160
Grass DMA [gm ]
<F 120 f~
Fig. 25. (a) Maize dry matter yield (DMY) vs ryegrass dry matter accumulation (DMA), (b)
ryegrass DMA vs maize leaf area index (LAI) under the LGM/Mech system at silage maturity.
Correlations are based on pooled data from three years, two levels of N supply (NllO and
N250), and four replicates (= 24 cases). *** significant at p = 0.001.
62
4.3 Discussion and conclusions
4.3.1 Nitrogen status during maize development
To successfully grow maize in LGM systems, it is necessary to reduce
interference by grass. Connell (1990) defined competition as the negative interaction
between two individuals or populations. Plants may compete for light, nutrients, and
water (Trenbath, 1976). This interference generally reduces the yields of species in
mixtures as compared to monocrop yields (Willey, 1979). Investigations of maize grown
in LGM systems indicated that water and N are important factors in competition (Kurtz
et al., 1952; Stivers, 1956; Pendleton et al., 1957; Ammon et al., 1995b). In chapter 3,
it was shown that increasing the N input from N110 to N250 almost eliminated the
variation in maize yield among the cropping systems, suggesting that, with moderate N
inputs (N110), N is the most limiting factor for maize DM production especially for
maize in the LGM systems (Fig. 4). Results demonstrate that differences in the plant N
status between CC and maize grown in the LGM/Chem and LGM/Mech systems
occurred at very early stages of maize development, although more fertilizer N
(averaged across the years, 56 kg N ha"1 was surface applied and placed in the rows)
was used in the LGM systems to compensate for the low mineral N content of the soil
immediately after maize sowing (Figs 18 to 20). Maize in the LGM systems showed a
low PN03C and PNC relative to CC as early as the 3rd leaf stage with Nl 10 and N250
respectively and at the 6th leaf stage with moderate inputs of N (Figs 18 to 20). It is
possible that when no N fertilizer is added at maize sowing, N deficiency may occur at
even earlier stages. Thus, lower PNC was detected for maize grown on the LGM plots
than for maize on the CC plots already on the first sampling date (Figs 18 and 19).
Schubiger et al. (1995) reported that, in LGM/Mech system (a mixture of grasses was
used as living mulch), very low concentrations of N and nitrate were found in the maize
tissues at early stages of development as compared to CC. In the present study, the early
N deficiency of maize plants grown on LGM plots also affected the PNAR and CGR
as compared to maize on CC plots (Figs 12 to 15). Only when high fertilizer N
applications were carried out, were the differences between the treatments small.
However, DM formation and N accumulation were clearly higher for maize grown on
the CC plots than for maize on the LGM plots, irrespective of the level of N supply
(Figs 16 and 17). This is probably due to the fact that maize grown on CC plots
maintained a superior plant N status throughout the growing season, irrespective the
levels of N supply (Figs 18 to 20). Wagger and Mengel (1988) and Thorup-Kristensen
(1993b) reported that cover crops may influence the N supply to the succeeding crops,
because they remove N from the autumn or spring soil mineral N pool, thus causing pre¬
emptive competition for N to the following main crop. Prior to maize sowing, the
63
mineral N content of the soil under Italian ryegrass stands was 19 kg ha"1 in this study,
whereas on ploughed plots, it was 74 kg N ha"1 (average of three years) (Table 15). The
pre-emptive competition for N increases if the grass is removed before maize sowing,
because N bound in the organic matter of the harvested grass will not be available to
the following main crop. Averaged across the years, the N yield of the Italian ryegrass
was approximately 52 kg N ha'1 just before maize sowing (Fig. 10 b). Moschler et al.
(1967) and Frye et al. (1988) reported that removing the cover crop for silage or hay
rather than leaving the sod on the ground for dead mulch or green manure reduced
maize grain yields. In the present study, N deficiency for maize grown in LGM systems
may not be a result of a pre-emptive N competition only, but also a result of
competition of ryegrass for N during the intercropping season. It should be noted that
adding N fertilizer increased the NA, NC, and N03C of the ryegrass strips even though
the N fertilizer was placed in the maize rows (Table 11 and Figs 22 to 24). This
indicates that the ryegrass strips in both LGM/Mech and LGM/Chem were significant
sinks for fertilizer N (Table 11 and Figs 22, 23, and 24). However, the N uptake of
ryegrass under the LGM/Chem was surely reduced by the application of herbicides at
the 1st and 2nd leaf stages of maize development. Averaged across the years, the
ryegrass strips under LGM/Chem showed an increment in NA of about 8 kg N ha"1 from
the 1st to the 3rd leaf stage (Fig. 23). The extent of N immobilization in the present
experiments is a matter of conjecture. Nevertheless, it was suggested that maize in LGM
systems does not need any starter N fertilizer, because N bound in the grass stubble is
mineralized as a result of rototilling (Anonymous, 1994). This was not confirmed by the
present study which shows that, on unfertilized LGM plots, the mineral N content in the
soil is very low (Fig. 38). Rather, it is possible that rototilling of grass stubbles during
seedbed preparation caused immobilization of N due to its wide C/N ratio. Kurtz et al.
(1946) pointed out that, in living mulch systems, N fertilization before maize planting
is inappropriate, because existing living mulches show a faster N uptake than the newly
sown main crop.
Regulation of ryegrass by lethal herbicide applications improved the N uptake
of maize and reduced the competition by the ryegrass as compared to the mechanically
suppressed living ryegrass strips. Therefore, the PNAR, PNA, PNC, and PN03C (Figs
14, 15, 16, 17, 18, 19, and 20) of maize were greater under LGM/Chem than under
LGM/Mech, especially on unfertilized plots. This suggests that lethal herbicide
applications result in a better availability of N to the maize. Under LGM/Mech,
competition for soil resources may continue until maize silage maturity. Ennik and
Hofman (1983) and Millard et al. (1990) pointed out that frequent cutting of grass
reduces its root mass and, thus, underground competition. Therefore, it is assumed that,
after each mechanical regulation ("mulching"), competition by the ryegrass was reduced.
64
As mentioned above, the maize yield advantage of the CC system over living
clover mulch systems is smaller than that over the LGM systems (Fig. 4). One
advantage of using legumes as cover crops is that they add symbiotically fixed
atmospheric N to the soil (Frye et al., 1988), thus mitigating the competition between
the cover crop and the main crop for N. Measurements of leaf greenness (SPAD-
readings), carried out in 1993, indicated that unfertilized maize grown under LCM/Mech
had the same N status as maize under CC until the 6th leaf stage (Fig. 27). With
moderate N fertilizer applications (N110), maize in the LCM systems showed similar
(3rd leaf stage) or even higher (6th leaf stage) PNC than in the CC system (Figs 18 and
19). As in the LGM systems, the regulation method influenced the plant N status and
growth of maize (LCM/Chem > LCM/Mech) (Figs 12 to 19) due to the fact that white
clover under LCM/Mech was probably a stronger competitor for N and water than the
chemically suppressed white clover. McAuliffe et al. (1958) investigated the influence
of inorganic N on N fixation by legumes and concluded that competition between a
legume and a non-leguminous crop for N can occur when N fertilizer is added which
inhibits atmospheric N fixation and stimulates the legume to use mineral N from the
soil. Yield differences could be reduced or even eliminated by broadening the rototilled
strip. More N would then be released from the decaying clover residues, thus improving
the availability of N to the maize plants, and the underground competition (roots) for
N would be reduced. In evaluating the relative merits of the various systems, however,
it has to be kept in mind that fertilized LCM plots also received additional N fertilizer
(about 50 kg N ha"1) immediately after maize seeding in order to compensate for the low
N level in the soil (see chapter 2).
Under the DGM system, ryegrass does not directly compete with the maize,
because ryegrass was killed approximately four weeks before maize sowing. Therefore,
high soil N availability in the DGM plots (Figs 36 and 37) may have influenced the
plant N status and growth of maize (Figs 12 to 19). Figs 18 and 19 show that the PNC
of maize in DGM systems never fell below the concentration of the CC, independent of
the level of N supply. This high PNC resulted from the absence of competition by the
ryegrass and the release of mineral N from the ryegrass residues, but it may also have
resulted from the additional N fertilization (54 kg ha"1 more N were applied to DGM
than to CC) at maize sowing. Nevertheless, the DGM system did not accumulate more
DM and N than the CC (Figs 16 and 17). The lower plant density in the DGM system
(averaged across two years, CC: 9.4, LGM/Chem: 9.4, LGM/Mech: 9.2, and DGM: 8.9)
may account for the observation that the CGR, PNAR, RPDMA, and RPNA (Figs 12
to 17) were lower at early stages of maize development than under CC. The reduction
in plant density was caused by the infestation of wire worms (Agriotes sp.) which was
more extensive in the DGM system than in the other cropping systems (data not shown).
65
4.3.2 Maize and ryegrass competition
Results of the present study suggest that the growth of Italian ryegrass was,
indeed, affected by the LAI of maize (Fig. 25 b). This effect was detected for the most
part during the grain filling period. In 1993, precipitation was relatively high and well
distributed over the growing season (Fig. 2 and Table 3). This enabled the maize plants
to produce a large canopy, especially under high N fertilization (Fig. 21). The weather
conditions during grain filling, rainy, cloudy and low temperatures, delayed the silage
maturity of maize (Fig. 2). As a result, the ryegrass strips were very shaded for a long
period, thus reducing the competition of the Italian ryegrass and its formation of
biomass. In 1993 with N250, the biomass of ryegrass declined during grain filling to a
greater extent than in 1992 (Fig. 22). Wilda (1992) reported that the formation of tillers
of Italian ryegrass was reduced by decreasing the light intesity. Bassetti (1989) found
that high N fertilization, especially with long intervals between cuts, enhanced the
degeneration ofItalian ryegrass swards. Selecting maize varieties which develop a large
LAI, especially at early stages of maize development, may improve the control over the
living mulch.
Increasing the N supply increased the NC and N03C in the ryegrass (Fig. 24),
even though N was applied to the maize rows. Belowground competition begins when
the depletion zones of two adjacent root systems overlap. The spatial distribution of the
roots of intercrop components may affect the extent of competition (Trenbath, 1976;
Osiru and Kibira, 1979). In the present experiment, the ryegrass roots probably grew fast
into the tilled strip, thus competing with the maize for N. The strip tillage used in this
study produced a rotovated strip, 30 cm wide and 15 cm deep. Thus, a root-free ryegrass
strip, 15 cm wide and 15 cm deep, bordered the maize plants. However, under the
rotovated strip old ryegrass roots may not have been destroyed. The extent to which
widening the tilled strip would reduce the competition between ryegrass and maize roots
is not known. The rootless space resulting from the strip tillage was similar to the gaps
used in Wilda's investigation (1992). In gaps 15 cm wide, ryegrass roots colonized the
central part resulting in a moderate root density. In gaps 34 cm wide, 67% fewer roots
were detected than in the centre of 8 cm gaps. Wilda's data can be interpreted as an
indication that rotovated strips, about 60 cm wide, would reduce competition by the
Italian ryegrass to a large extent; as a result, the maize would use row-applied fertilizer
N more efficiently. The importance of width and depth of the rotovated strip in living
mulch systems with maize has not yet been investigated. This aspect should be
considered in future research programs dealing with living mulch systems.
4.3.3 Leaf area
There are only a few growth analyses of maize in living mulch systems. Figure
66
21 and Table 10 show that availability of N played an important role in the formation
of leaf area. The leaf area was extremely depressed in the LGM systems, although more
N was applied to the mulch seeding systems than to the CC plots. Furthermore, maize
in the LGM systems showed a lower specific leaf weight than maize grown on the CC
plots throughout the growing season (Table 13). This probably means that maize in the
LGM systems produced thinner leaves than CC maize, especially under low N supply
(Nl 10). Thus, it is suggested that the photosynthetic capacity of maize may have been
greater under CC than under the LGM systems because of a larger leaf area (Fig. 21),
thicker leaves (Table 13), and a higher concentration of leaf N (Table 14).
67
5 SPAD READINGS
5.1 Introduction
Environmental problems associated with high inputs of N fertilizer have
increased the need for an improved efficiency of N use by crops. Synchronizing
fertilizer N availability with maximum crop N uptake has been proposed as a way of
improving N use efficiency and of protecting groundwater (Blackmer et al., 1993).
Maize producers have adapted soil tests to determine the appropriate amounts of N
fertilizer. In Switzerland, the standard soil test is the so-called Nmin method. This
method reflects the actual amount of plant-available mineral N (N03-N plus NH4-N) in
the soil. However, soil analyses are costly and time-consuming, and the results
sometimes become available too late to correct N fertilization. Variable climatic
conditions between soil sampling and N uptake by the crop make it difficult for the
producer to decide on the amount of N fertilizer to apply. Thus, producers are inclined
to compensate for possible N deficiency by applying additional fertilizer to insure
adequate N for the crop (Schepers, 1990). Flexible N management systems, that can be
modified to compensate for climatic conditions, may offer environmental and
economical advantages over the above-mentioned strategy (Blackmer and Schepers,
1994). Chlorophyll meter has been identified as a convenient tool for evaluating the N
status of maize, because tight relationships between leaf chlorophyll content or relative
greenness and leaf N concentration were established, especially when N was deficient
(Girardin et al., 1985; Wolfe et al., 1988). The SPAD-502 (Soil and Plant Analyse
Developments) Chlorophyll Meter provides an instantaneous and non-destructive
indication of leaf chlorophyll. SPAD readings are based on the amount of light
transmitted by the leaf in two wavelength ranges (650 and 940 nm). Values measured
by this chlorophyll meter do not display the leaf chlorophyll concentration but do
provide a relative indication of leaf greenness (Schepers, 1990). In general, chlorophyll
meter readings and leaf greenness increase as N availability to the plant increases
(Blackmer et al., 1993). The present chapter aimed at determining whether chlorophyll
meter (SPAD-502) readings are good indicators of the N status of maize. Measurements
were conducted in various maize cropping systems throughout the growing season.
68
5.2 Results
5.2.1 SPAD readings
The results of the ANOVA for SPAD readings are depicted in Table 12. Levels
of N supply are shown separately in graphs to improve the clarity of the figures. With
N110, maize under CC had the greenest uppermost leaves from the third (1991), first
(1992), and fourth observation (1993) onwards (Figs 26 and 27). The third and fourth
SPAD measurements were carried out between the first and second sampling dates of
maize, i.e. between the 3rd and 6th leaf stage of maize. Differences between LGM/Mech
and LGM/Chem were found when the plants had almost reached (1992 and 1993) or
passed (1991) the 6th leaf stage. From these developmental stages onwards, the relative
chlorophyll contents in the uppermost leaf were slightly (1992) or clearly (1991 and
1993) higher under LGM/Chem relative to LGM/Mech. With N250, considerable
variation among the cropping systems was observed in 1991 only. In that year, SPAD
readings were clearly lower under LGM/Mech as compared to CC and LGM/Chem.
These differences, however, did not occur in the other experimental years. In 1991, there
was very low rainfall during the period in which the N fertilizer was applied from about
the 4th to the 9th leaf stage (see Fig. 2). As a result, the N supply effects became
significant only at later stages of development (i.e. at 9th leaf stage = 539 GDD) (Table
12). In contrast, in 1992 and 1993, the effects of N supply appeared at about the 6th leaf
stage (6th leaf stage = 351 GDD in 1992 and 364 GDD in 1993). The cropping system
x N supply interaction was significant after the 9th leaf stage in 1991 (9th leaf stage =
539 GDD) and after the 6th leaf stage in 1992 and 1993.
In 1993, an NO level was included in the experiment (Fig. 27). Conventionally
grown maize and maize sown in a living clover mulch (LCM/Mech) showed similar leaf
greenness at very early stages of maize development (before the 3rd leaf stage).
Afterwards, CC had the highest values. In the LCM/Mech system, the greenness of the
uppermost leaves decreased at about the 9th leaf stage, but they were still greener than
those in the LGM systems. Under LGM/Chem and LGM/Mech, the readings were very
low from the first measurement onwards. No differences between LGM systems were
observed until the 3rd leaf stage of maize development. Thereafter, the SPAD readings
were higher under LGM/Chem than under LGM/Mech.
5.2.2 Relationship between SPAD values and other maize traits
Relationships between SPAD readings and N concentration in the uppermost
fully expanded leaves (LNC) at pollen shedding are shown in Figs 28 a and b. The
SPAD measurements were highly and positively correlated with the LNC.
respectively.
1993
and
1992
1991,
for
1155
1190,
1184,
=maturity
silage
630,
634,
681,
=shedding
pollen
505,
486,
539,
=stage
leaf
9th
364,
351,
378,
=stage
leaf
6th
234,
217,
161,
=stage
leaf
3rd
[°C];
days
degree
growing
=GDD
2supply.
Nof
level
=N
system;
crop
ping
=CS
'si
gnif
ican
t.not
=ns
respectively,
0.001
and
0.01,
0.05,
=p
at
significant
***
**,
*,
—~
——
***
***
***
1178
——
——
._
__
—__
***
***
***
1118
__
„„
__
._
__
—__
***
***
***
1028
„._
__
__
***
***
***
950
***
«**
***
943
***
***
***
1059
***
***
***
862
***
***
***
836
***
***
***
944
***
***
***
766
***
***
***
732
***
***
***
861
***
***
***
630
***
***
*563
***
***
***
789
***
***
***
569
***
***
**
511
***
***
***
605
ns
*ns
465
****
**
427
ns
***
***
539
ns
**
***
390
ns
ns
***
375
ns
ns
***
471
ns
ns
**
329
ns
****
324
ns
ns
***
392
ns
ns
ns
263
ns
ns
ns
254
ns
ns
ns
294
ns
ns
ns
189
ns
ns
*213
ns
ns
*213
ns
ns
***
152
ns
ns
***
153
ns
ns
***
150
xN
CS
NCS
GDD2
xN
CS
NCS
GDD2
xN
CS
NCS
GDD2
variation1
of
Source
variation1
of
Source
variation1
of
Source
1993
1992
1991
period.
crop
ping
each
at
and
maize
of
season
grow
ing
the
thro
ugho
ut(SPAD-502)
readings
meter
chlo
roph
yll
on
supp
lyN
of
level
and
systems
cropping
between
interactions
the
and
N250),
and
10
(NI
supp
lyN
of
level
LGM/Mech),
LGM/Chem,
(CC,
systems
cropping
of
effects
the
of
Sign
ific
ance
12.
Table
70
50
|P 40
"a8
°< 30
20 -
—->—i—>—i—'—i—'—r
N110 91
cc
LGM/Chem
LGM/Mech
300
Growing degree days [°Cd]
600 900 1200
Fig. 26. Seasonal changes in SPAD readings of the uppermost fully expanded leaves of silagemaize in three cropping systems. The cropping systems and levels of N supply are explained in
Materials and Methods. Bars are LSD (0.05) values. 3rd, 6th, 9th = leaf stages, PS = pollenshedding.
In 1992 (Fig. 28 a), however, the correlation coefficient was higher than in 1993. This
may be due to the fact that the sampling dates were different each year (in 1992 leaf
samplings were carried out about 15 days after pollen shedding). Another reason may
be that, in 1993, an NO level was included in the data. However, without NO, the
relationship between SPAD readings and LNC increased to r = 0.96***. For CC under
10 I 1 I 1 I I I I I I I I 1 I 1 I
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°Cd]
Fig. 27. Seasonal changes in SPAD readings of the uppermost fully expanded leaves of silagemaize under various cropping systems. The cropping systems and levels of N supply are
explained in Materials and Methods. Bars are LSD (0.05) values. 3rd, 6th, 9th = leaf stages, PS
= pollen shedding.
o CCN0
o CCN110
• CCN250
o LGM/ChemNO
LGM/ChemNUO
LGM/ChemN250
A LGM/MechNO
A LGM/MechNllO
LGM/MechN250
1.5 2.0 2.5 3.0 3.5 1.5 2.0 2.5 3.0 3.5
LNC [%} LNC[%]
Fig. 28. Linear regression of chlorophyll meter readings (SPAD readings) on maize leaf N
concentrations (LNC) under three cropping systems at pollen shedding. Both traits were
measured on the uppermost fully expanded leaves, (a) = measurements in 1992, including data
for N110 and N250, (b) = measurements in 1993, including data for NO, Nl 10, and N250. ***
= significant at p = 0.001.
NO, the SPAD values consistently overestimated the LNC; all four replicates (= open
circles) are above the regression line (Fig. 28 b).
601 I ' I ' I ' I ' r ' I ' I ' I '
r = 0.93***
72
One factor that may cause variability in the linear relationship between LNC and
chlorophyll meter readings is leaf thickness (Peng et al., 1993; Blackmer et al., 1994).
Leaf thickness is difficult to measure, but it is related to the specific leaf weight (SLW
= leaf weight per unit leaf area) (Chiariello et al., 1989). The whole canopy specific leaf
weight (SLW) was calculated from the total green leaf area and leaf dry weight of the
maize shoots (Table 13). At the first sampling (i.e. the 3rd leaf stage of maize), only the
effects of the cropping system were considered in ANOVA because, until this stage, all
plots had received the same amount ofN fertilizer. The data presented in Table 13 show
that the SLW was different for the cropping systems at very early stages of maize
development. In both years, the thickest leaves were found for maize under CC
throughout the growing season. There were no consistent differences between
LGM/Mech and LGM/Chem. Increasing the N supply from N110 to N250 reduced the
differences between the cropping systems. Under CC, the variation between N110 and
N250 was fairly small, whereas under LGM/Mech and LGM/Chem, they were
consistently higher. At pollen shedding, highly significant variations were observed
among the cropping systems and levels of N supply. Throughout the growing seasons
of 1992 and 1993 there were no significant interactions between cropping system and
N supply.
Table 14 shows the relationships between the SPAD readings, the LNC, and the
SLW within the cropping systems at pollen shedding. In both years, the tightest
relationships between the SPAD readings and the LNC occurred under LGM/Mech.
Under CC, no significant relationships were found between SPAD meter readings and
the SLW. Tight positive relationships were found between SLW and whole plant N
accumulation (PNA) and whole plant N concentration (PNC) under LGM/Mech and
LGM/Chem, while, under CC, no relationships were found.
5.2.3 Prediction of maize silage yield and N yield
SPAD values were also good predictors of the maize silage yield and N yield
(Fig. 29). In 1991 and 1992, the relationships between SPAD readings and the DMY and
N yield were significant at P < 0.05 from the 6th leaf stage of maize onwards. In 1993,
significant correlation coefficients were already obtained at the very beginning of the
growing season until the last SPAD reading; highly significant correlations coefficients
(r > 0.8 ) occurred after the 6th leaf stage of maize development onwards, surely
because the last application of N had been carried out to the N250 plots. Therefore,
correlation coefficients increased from 0.8 to 0.9. In 1992, high correlation coefficients
(r > 0.8) were also found after the 6th leaf stage, and in 1991, comparable correlation
coefficients were obtained from the 9th leaf stage onwards. In comparing the years, it
considered.
not
were
level
Nx
systems
cropping
and
levels
Nstage
leaf
3rd
the
At
'ma
turi
ty.
sila
ge=
SM
shedding;
pollen
=PS
stages;
leaf
=9th
and
6th,
3rd,
Methods.
and
Materials
in
explained
are
supply
Nof
levels
and
systems
cropping
The
sign
ific
ant.
not
=ns
0.001.
and
0.01
,0.05,
=p
at
significant
***
**,
*,
ns
ns
ns
ns
—ns
ns
ns
ns
—
**
***
ns
ns
-
ns
***
ns
ns
-
***
**
ns
**
**
***
***
**
»*
--
2.0
~~
——
2.0
——
—
62.3
50.1
42.0
37.7
31.2
62.7
50.5
42.4
35.1
29.2
58.4
46.0
40.6
37.5
30.0
60.7
47.1
41.1
34.1
29.2
4.0
2.0
2.0
—1.0
4.0
2.0
2.0
2.0
3.0
58.2
46.6
40.5
38.1
31.3
60.5
47.8
39.3
34.7
28.3
59.9
46.7
39.7
36.6
29.5
59.2
45.8
40.5
32.2
26.9
°
63.7
50.8
43.7
38.1
31.7
65.5
52.8
45.5
37.0
32.4
—-
——
2.0
—3.0
4.0
4.0
—
60.9
49.6
41.2
37.6
32.5
63.1
49.6
39.8
35.4
28.4
62.2
49.1
41.5
36.7
29.7
60.1
48.2
41.2
31.6
26.5
65.3
51.6
43.3
38.7
32.7
64.9
53.7
46.2
38.2
32.7
5.0
2.0
4.0
--
3.0
4.0
4.0
--
3.0
55.6
43.7
39.9
38.7
30.2
57.8
45.9
38.8
34.0
28.1
57.6
44.3
38.0
36.4
29.3
58.2
43.5
39.8
32.7
27.3
62.1
50.0
44.1
37.5
30.6
66.0
51.8
44.8
35.7
32.2
SM
PS
9th
6th
3rd1
SM
PS
9th
6th
3rd1
level
Nx
system
Cropping
levels
Nitr
ogen
systems
Cropping
ANOVA
N250
N110
levels
Nitrogen
LGM/Mech
LGM/Chem
CC
systems
Cropping
LSD(
005)
N250
xLGM/Mech
N250
xLGM/Chem
N250
xCC
LSD(
005)
xNHO
LGM/Mech
10
xNl
LGM/Chem
CCxNllO
level
Nx
system
Cropping
1993
1992
supply.
Nof
levels
Ntwo
at
systems
crop
ping
different
under
grown
maize
of
m'2]
[gweight
leaf
specific
canopy
Whole
13.
Table
74
Table 14. Correlations between SPAD readings, N concentrations in the uppermost fullyexpanded leaves (LNC), whole canopy specific leaf weight (SLW), whole plant N accumulation
(PNA), and whole plant N concentrations (PNC) respectively under three maize cropping systemswith Nl 10 and N250 at pollen shedding.
19921 1993
CC LGM/Chem LGM/Mech CC LGM/Chem LGM/Mech
SPAD
vs
LNC +0.80 * +0.97 *** +0 99 *** +0.77 * jA QT *** +0.99 ***
SLW +0.69 +0.92 ** +0.82* -0.17 +0.87 ** +0 94 ***
SLW
vs
PNA +0.48 +0.93 *** +0.78 * +0.28 +0.89 ** +0.96 ***
PNC +0.28 +0.93 *** +0.73 * +0.01 +0.89 ** +0.93 ***
1SPAD readings were obtained a few days after the harvest of maize at pollen shedding. *, **,
*** significant atp = 0.05, 0.01, and 0.001 respectively. Correlations are based on two levels
of N supply (Nl lO and N250) and four replicates (= 8 cases) for each cropping system. CC =
conventional cropping; LGM/Chem = living grass mulch, chemically killed; LGM/Mech = livinggrass mulch, mechanically regulated .
must be considered that, in the 1993 experiment, including the NO treatment con¬
siderably widened the range of soil N conditions. This improved the predictive value of
the SPAD readings, especially during early stages of maize development: after exclusion
of the NO level from the analysis, the correlations were significant only after the 6th leaf
stage. A breakdown according to the cropping systems showed that the relationships
between the SPAD readings and the DMY and N yield were not consistent on the CC
plots, irrespective of the stage of development and cropping year (Fig. 30). Under
LGM/Mech and LGM/Chem, however, highly significant correlations existed from the
9th leaf stage onwards in 1991 and from the 6th leaf until the last SPAD reading in
1992 and 1993. The breakdown according to N supply, conducted for the data collected
in 1993, showed that the correlation coefficients declined as follows: NO > N110 >
N250 (data not shown).
75
1.00
0.75
•3 0.50 -
B
8 0.25 - 3(h
I•3 0.00 -
-0.25 -
-0.50
1991...t
9th
6th
PS
-•- DMY
-O— N yield
_L _L _L _L
300 600 900 1200
1.00
0.75
—i 1 1 1 r
1992
- i*h 6th
0.50 -
0.25
0.00
3th1
PS
,9th
J i L
300 600 900 1200
Growing degree days [°C d]
300 600 900 1200
Growing degree days [°C d]
Fig. 29. Prediction of DMY and N yield from SPAD 502 readings in 1991 (a), 1992 (b), and
1993 (c) based on pooled data from three cropping systems, two (a, b) or three (c) levels of N
supply, and four replicates. Dotted line indicates the r (0.05) level. 3rd, 6th, 9th = leaf stages,PS = pollen shedding.
76
300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig 30 Prediction of DMY and N yield from SPAD 502 readings based on data for each
cropping system, two levels of N supply, and four replicates CC (a, b and c), LGM/Chem (d,e and f). LGM/Mech (g, h and l) Dotted line indicates the r (0 05) level
77
5.3 Discussion and conclusions
5.3.1 Determination of plant N status
Caution should be exercised in interpreting the changes in SPAD readings over
time, because they were made on different leaves. Piekielek and Fox (1992) and Smeal
and Zhang (1994) found that the SPAD readings increased with increasing leaf number.
In a study with two selected maize hybrids, Schepers et al. (1992) observed that the
shape of the regression curve (SPAD readings on LNC) changed with time and that the
calibration curves were different depending on the hybrids used. Thus, comparisons
should be made at a given growth stage. In order to correct N deficiency of crops,
depletion of N in plant tissues must be detected early enough to avoid reductions in
yield (Blackmer and Schepers, 1994). Results in chapter 4 showed that the whole plant
nitrate concentration (PN03C) was positively correlated with the yields of DM and N
from the first sampling (i.e. 3rd leaf stage) until maize silage maturity in 1992 and 1993
(Table 10), whereas in 1991 positive correlations were found from the 6th leaf stage
onwards (Table 9). The results suggest that tissue testing for nitrate is an appropriate
method for determining the N status of maize which provides the necessary information
in good time. Iversen et al. (1985) and McClenahan and Killom (1988) reported that
basal stem nitrate concentrations of young plants were positively correlated with grain
yield. Plant N concentration has also been proposed as a method to identify N
deficiencies in young maize plants. In fact, results in Tables 9 and 10 show that the
whole plant N concentration (PNC) was positively correlated with the yields of DM and
N from the 6th leaf stage until maize silage maturity. Cerrato and Blackmer (1991) and
Binford et al. (1992) report, however, that the concentration of N is not a sensitive
indicator of the N status of maize plants, at least at high soil N availability. It has been
pointed out that plant tissue assays for nitrate and total N are laborious, time-consuming,
costly, and may give different results (McClenahan and Killorn, 1988; Schepers et al.,
1990b). In contrast, determination of the plant N status with the chlorophyll meter
SPAD-502 is simple, fast, and non-destructive. Blackmer and Schepers (1994) stated that
the SPAD values enable early detection of N deficiency. According to the results
obtained in this study, the SPAD meter also indicated the emerging N deficiency of
maize planted on LGM plots (Figs 26 and 27), suggesting that tissue testing with the
SPAD-502 is a tool that can aid in fertilizer N management. The SPAD readings showed
that the uppermost fully expanded leaves were paler for sod-planted maize than for
maize under CC (Figs 26 and 27). Nitrogen deficiencies result in decreased amounts of
leaf chlorophyll; lower SPAD values are, therefore indicative of low N concentrations
in the leaves (Blackmer et al., 1994). In agreement with the SPAD readings, PNC was
found to be lower under LGM/Chem and LGM/Mech than under CC from the second
78
sampling onwards (Figs 18 and 19) with N110 and N250. In line with Blackmer and
Schepers (1994), SPAD readings can clearly identify differences in the N status of maize
on unfertilized plots. In 1993, LGM systems on NO plots (Fig. 27) showed paler
uppermost leaves than CC and the LCM/Mech systems from the first measurement
onwards. The chlorophyll meter indicated that competition was exerted by the Italian
ryegrass: at the NO level (Fig. 27), LGM/Chem started to differ from LGM/Mech after
the last herbicide application (i.e. 3th leaf stage), whereas under N110 the maize in
LGM/Chem plots had greener leaves than maize grown under the LGM/Mech after the
6th leaf stage onwards (Figs 26 and 27). Only under N250, and with the exception of
1991, were SPAD readings unable to discriminate the LGM systems.
5.3.2 SPAD readings and leaf thickness
Positive relationships between SPAD readings and LNC for maize (Fig. 29) have
also been reported by Schepers et al. (1990a), Follett et al. (1992), and Wood et al.
(1992). According to Dwyer et al. (1991), chlorophyll meter readings and extractable
chlorophyll concentration are highly and positively correlated. However, variation in leaf
thickness may confound the linear relationship between chlorophyll meter readings and
the LNC. Adjusting SPAD values for the SLW, however, could improve the estimation
of the LNC (Peng et al., 1993; Blackmer et al., 1994). In fact, the prediction of the N
concentrations in rice from SPAD readings, taken at various developmental stages and
on different cultivars, improved considerably when corrections were made for
differences in specific leaf weight (Peng et al., 1993). In agreement with Blackmer et
al. (1994), the results in Table 13 show that the SLW tended to increase with increasing
applications of N fertilizer, at least for leaves formed under the LGM plots. Correlation
coefficients at pollen shedding verified that SPAD values and the SLW were tightly
related in LGM systems, whereas under CC no significant correlations were found
(Table 14). The lack of a pronounced response of maize under CC to N fertilization can
be traced to the fact that, even under Nl 10, the Nmin supply and distribution in the soil
(Fig. 32) was almost sufficient for maximum DM production (Fig. 4). This lack of
response was also reflected by the relationships between SLW and PNA and PNC (Table
14), as found under CC. The cropping method under which the plant-internal N supply
was highest (CC) also produced plants with the highest SLW, a phenomenon that was
observed throughout the growing season (Table 13). It is assumed, therefore, that the
high SPAD values for CC maize resulted from a higher chlorophyll concentration in the
leaves of maize and also from slightly thicker leaves. Unfortunately, SLW was not
determined for plants that were grown on the NO plots. Therefore, the reason why the
SPAD readings consistently overestimated the LNC of the plants on the unfertilized CC
plots cannot be given (Fig. 28 b). It is possible that variation in leaf thickness or SLW
79
contributed to the inaccurate prediction of N concentration by the SPAD instrument. The
importance of leaf thickness suggests that better correlations between chlorophyll meter
readings and leaf N status would be obtained if the specific leaf N (N content per unit
area) were to be used as an indicator of the N status rather than the LNC. However,
transforming the LNC to an area basis (i.e. specific leaf area) provided an inferior
relationship with grain yield as compared with LNC (Blackmer et al., 1994).
5.3.3 Cropping systems and SPAD readings
In the present study, SPAD values were highly correlated with DMY and N yield
when data for the various cropping systems were pooled (Fig. 29). However, the
relationships of SPAD values with LNC (Table 14), DMY, and N yield of maize (Fig.
30) were different for the cropping systems. Relationships between SPAD readings and
LNC under CC were less tight than those under the LGM systems (Table 14). Under
LGM/Mech, an almost perfect relationship (r = +0.99) was found. According to Follett
et al. (1992), Schepers et al. (1992), and Piekielek et al. (1995), factors such as location,
crop growth stages, hybrid differences, timing of N fertilizer application, availability of
water and N, and cultural practices may have an effect on leaf greenness and the
resulting chlorophyll meter readings. The reason why the SPAD - DMY relationship was
weak under CC may be that the soil mineral N concentration was nearly sufficient for
maximum growth at all N rates (= NO, Nl 10, N250); thus, there was only little variation
in SPAD readings, LNC, and PNC. Schepers et al. (1992) and Blackmer et al. (1994)
reported that chlorophyll meters are insensitive to high levels ofN supply. It is possible,
therefore, that SPAD readings are poor predictors of maize DMY and N yield under CC
because of luxury consumption of N (Fig. 30). Follett et al. (1992) reported a positive
association between chlorophyll meter readings and Nmin concentration in the soil
solution. In the experiment of 1993, correlation coefficients of pooled data within N
supply levels declined in the following order: NO > Nl 10 > N250 (data not shown).
Normalizing the SPAD values to relative terms (i.e. SPAD data relative to an adequately
fertilized area of the field) may facilitate better comparisons between hybrids, stages of
growth, localities, and cultural practices (Schepers, 1990; Follett et al., 1992; Schepers
et al., 1992; Smeal and Zhang, 1994; Blackmer et al., 1995).
80
6 Nmin CONCENTRATION IN THE SOIL
6.1 Introduction
Large amounts of nitrate may be leached into the groundwater in a winter fallow
system, thus envolving public concerned about the contamination of groundwater by
nitrate. Working the soil in autumn may increase the mineralization of organically bound
N (Dowdell et al., 1983; Christian and Ball, 1994), thus increasing the nitrate leaching
hazard. Farmers can decrease nitrate leaching during the cool season by sowing cover
crops after the harvest of the summer crop (Mouraux et al., 1992; Masse et al., 1994;
Ammon et al., 1995b). Among other purposes, cover crops during the winter are used
to absorb and store N that would otherwise be leached into the groundwater (Dgen,
1990; Hoyt and Mikkelsen, 1991). Nitrogen bound in the cover crop may become
available to the next crop if it is released during the period when the main crop is able
to absorb N from the soil (Doran and Smith, 1991). The realease of N from winter cover
crop residues is affected by climate and soil, type of cover crop, C/N ratio, and tillage
management practices (Wagger, 1989; Drury et al., 1991; Torbert and Reeves, 1991;
Riiegg, 1994). Nitrate leaching may also occur during the early growing season of
maize. The nitrate leaching problem can be reduced if the maize is sown into live cover
crops. There are contradictory conclusions on the effects of living mulches on the yield
of maize (Robertson et al., 1976; Elkins et al., 1983; Nicholson and Wien, 1983). Crops
covering the soil between the maize rows may compete with the main crop for growth
factors such as water and N. Most of the published research deals with the effects of
killed winter cover crops on the availability of N for the following main crop (Vos,
1992; Jackson et al., 1993). Only limited information exists on the effects of living
cover crop mulches on the seasonal patterns of the Nmin concentration in soils planted
with maize (Crozier et al., 1994). This chapter focuses, therefore, on the temporal
changes in and the spatial distribution of Nmin in the soil and their possible effects on
maize plants.
81
6.2 Results
6.2.1 Nmin content of the soil before maize sowing
Accumulation of DM and N in the shoots of Italian ryegrass and the contents of
soil Nmin (0 to 90 cm depth) in March and at the spring cutting are shown in Table 15.
The average NA of ryegrass (= period from autumn cutting to spring cutting) was 52
kg N ha'1. Of this amount, 38 kg N ha"1 was accumulated as early as March.
Table 15. Dry matter and N in the shoots of Italian ryegrass and Nmin content (0 to 90 cm
depth) under ploughed plots and ryegrass stands in mid March and immediately before the springcutting of the ryegrass.
Cover crop
March
DMA NA Nmin
Spring cutting
DMA NA Nmin
1991
PloughRyegrassLSD
(005)
significance
1992
PloughRyegrassLSD
(0 05)
significance
1993
PloughRyegrassLSD
(005)
significance
mean
PloughRyegrassLSD
(005)
significance
LSD(005)
significance
1.49 38
1.85 48
1.24 29
1.53
0.37
38
43 70
17 3.08 38 23
19 14* **
103 84
27 4.86 77 23
19 17** **
53 69
20 3.67 40 11
6 18*** **
66 74
21 3.87 52 19
— 18
ns**
0.28 6*** ***
DMA = DM accumulation [t ha'1]; NA = N accumulation [kg ha'1]; Nmin = soil mineral N
content [kg ha"1]. *, **, *** significant atp = 0.05, 0.01, and 0.001 respectively.' LSD values
are for comparisons of the Nmin content in ploughed plots and ryegrass stands.2LSD values
are for comparisons of the DMA and NA of ryegrass among the years.
82
Table 16 Nmin content and distribution in the top soil (0 to 30 cm) and sub soil layers (30 to
60 cm and 60 to 90 cm) under ploughed plots and in ryegrass stands in mid March and
immediately before the spring cutting of the ryegrass
March Spring cutting
Depth cm Plough grass significance Plough grass significance
1991
0-30 22 10
30-60 12 4
60-90 9 3
LSD(005)significance
3***
1***
1992
0-30 46 13
30-60 28 6
60-90 29 8
LSD(005)significance
8**
3
**
1993
0-30 37 12
30-60 11 4
60-90 5 4
LSD(0 05)
significance
5***
1***
mean
0-30 35 12
30-60 17 5
60-90 14 5
Nmin content in kg ha' *, **, *** significant at p = 0 05, 0 01, and 0 001 respectively ns =
not significant
At March and at the spring cutting, the Nmin content of the soil was higher under the
ploughed plots than under the ryegrass stands in all years Averaged across the years,
the Nmin content of the ploughed plots in March was 66 kg N ha ', whereas it was only
21 kg N ha'under the ryegrass stands Until the spring cutting, the Nmin content of the
ploughed plots increased by 8 kg N ha' (to 74 kg N ha'), while under the ryegrass
stands it decreased to 19 kg N ha'
The Nmin contents of the various soil layers shortly before maize sowing are
presented in Table 16 In all years, ploughed and ryegrass plots showed higher Nmin
values in the top soil (0 to 30 cm depth) than in the sub soil layers (30 to 60 cm and
60 to 90 cm depth) on both sampling dates
ns
ns
ns
37 14
20 5
13 4
4 3*** ***
38 16 **
22 4 **
24 3 **;
5 1
*** ***
40 4
21 4
8 3
8 —
***
38 11 *
21 4 **
15 3 ns
83
Table 17. Combined ANOVA over years for the Nmin concentration in the maize row (location
A). The ANOVA is based on three experimental years (1991, 1992, 1993), two levels of N
supply, and three cropping systems at each developmental stage of maize development.
In the maize rows / source of variation1
Depth / Stage2 Y N CS YxN YxCS Nx CS Y x N x CS
0to90
3rd ns — ns — ns — —
6th * * **ns ns ns ns
9th *** * ** **ns
*ns
PS ***ns ns
***ns ns ns
SM ***ns ns
***ns ns ns
0to30
3rd ***- ns - ns -- -
6th ns*
ns ns ns ns ns
9th *** * * ** ns*
ns
PS *** ** *
SM ***ns ns
***
***
ns
ns
ns
ns
ns
ns
30 to 60
3rd **—
*-
**— -
6th *ns
**ns ns ns ns
9th * * ** **ns ns ns
PS *ns
*ns ns ns ns
SM *ns ns ns ns ns ns
60 to 90
3rd ns — ns -*
- -
6th ** ns * **ns ns ns
9th ** ** **ns
*ns ns
PS *** * *ns ns ns ns
SM *ns
**ns ns
**ns
Nmin concentration = mg kg-1 dry soil. *, **, *** significant at p = 0.05, 0.01, and 0.001
respectively, ns = not significant.' Y = year; N = level of N supply (N110, N250); CS =
cropping system (CC, LGM/Chem, LGM/Mech).2 Depth = cm; Stage: 3rd, 6th, and 9th = leaf
stages; PS = pollen shedding; SM = silage maturity.
In the top soil, ploughed plots averaged 35 kg N ha'1 in March and 38 kg N ha"1
immediately before the spring cutting, whereas under the ryegrass stands the Nmin
values were about 11 kg N ha'1 on both sampling dates. In the sub soil layers (at depths
of 30 to 60 cm and 60 to 90 cm), the Italian ryegrass almost depleted the soil Nmin
pool already in March, while the Nmin content was relatively high under ploughed plots.
At the spring cutting and in the sub soil layers, ploughed plots showed an increment in
the Nmin content of 5 kg N ha'1 (36 kg N ha"1), whereas under ryegrass stands a
decrease of about 2 kg N ha"1 was observed.
84
Table 18. Combined ANOVA over years for the Nmin concentration 19 cm from the maize row
(location B). The ANOVA is based on two experimental years (1992, 1993), two levels of N
supply, and three cropping systems at each developmental stage of maize development.
19 cm from the maize row / source of variation1
Depth / Stage2 Y N CS Yx N YxCS NxCS Y x N x CS
0to90
3rd ns —**
— ns - -
6th ns ns***
ns ns ns ns
9th ns ns**
ns ns*
ns
PS ***ns ns
* **ns ns
SM ns ns ns ns**
ns**
0to30
3rd *—
*- ns — —
6th ns ns**
ns ns ns ns
9th ns ns**
ns ns*
ns
PS **ns ns ns ns ns ns
SM ns ns ns* **
ns**
30 to 60
3rd ns —
**- ns - -
6th ns ns**
ns ns ns ns
9th * * **ns ns ns ns
PS ***ns ns ns
***ns ns
SM *ns ns *
ns ns ns
60 to 90
3rd ns --*
- ns - --
6th ns ns*
ns ns ns ns
9th **ns ns ns
**ns ns
PS ***ns ns ns
***ns ns
SM ***ns
*ns ns
*ns
Nmin concentration = mg kg-1 dry soil. *, **, *** significant at p = 0.05, 0.01, and 0.001
respectively, ns = not significant.'Y = year; N = level of N supply (N110, N250); CS =
cropping system (CC, LGM/Chem, LGM/Mech).2 Depth = cm; Stage: 3rd, 6th, and 9th = leaf
stages; PS = pollen shedding; SM = silage maturity.
6.2.2 Concentration and spatial distribution of Nmin during the growing season of
maize
Concentrations and spatial distribution of Nmin in the soil solution during maize
development are presented in Figs 31 to 40. The scales of the Y axes are different for
the soil layers in order to improve the clarity of the figures. Averages across the years
are shown in Fig. 31. Even though the Nmin samplings were carried out at slightly
different physiological stages, as can be deduced from the slightly varying growing
degree days (see Chapter 2, Table 3), the Nmin concentration in the soil at the various
sampling locations was only slightly affected by the year x N supply x cropping system
85
Table 19 Combined ANOVA over years for the Nmin concentration 38 cm from the maize row
(location C) The ANOVA is based on three expenmenal years (1991, 1992, 1993), two levels
of N supply, and three cropping systems at each developmental stage of maize development
38 cm from the maize row / source of variation1
Depth / Stage2 Y N CS Yx N YxCS NxCS Y x N x CS
0to90
3rd *—
**—
**— —
6th ns ns***
ns ns ns ns
9th *ns
***ns ns
*ns
PS ***ns
*ns
*ns ns
SM ns ns ns*** *
ns*
0to30
3rd ***—
*—
***— —
6th ns ns**
ns**
ns ns
9th ns ns***
ns ns ns ns
PS **ns ns ns ns ns ns
SM ns ns ns***
ns ns*
30 to 60
3rd ns -***
- ns - -
6th ns ns*** ns ns ns ns
9th ** * ***ns ns
*ns
PS **ns
**ns
*ns ns
SM *ns
* *** *ns
*
60 to 90
3rd ns -***
- ns - -
6th ***ns ns ns
***ns ns
9th ***ns
**ns
***ns ns
PS **ns
*ns
***ns ns
SM ns ns*
ns* *
ns
Nmin concentration = mg kg-1 dry soil *, **, *** significant at p = 0 05, 001, and 0001
respectively ns = not significant'Y = year, N = level of N supply (N110, N250), CS =
cropping system (CC, LGM/Chem, LGM/Mech)2Depth = cm, Stage 3rd, 6th, and 9th = leaf
stages, PS = pollen shedding, SM = silage maturity
interaction and the N supply x cropping system interaction (Tables 17, 18, and 19) At
the 3rd leaf stage, only the effects of the cropping systems were considered, because at
this developmental stage, the Nl 10 and N250 plots were supplied with the same amount
of N fertilizer Because of the frequent absence of significant interactions between N
supply and cropping systems, averages across years and rates ofN application are shown
in Figs 32 and 33 In interpreting the data m Figs 32 and 33 it must be taken into
account that the cropping system effects were often non-significant, because there were
significant year x cropping system effects For the locations A (sampling in the maize
rows) and C (sampling 38 cm from die maize rows), the averages across the years 1991,
60
§ 40
'St 20
25
20
15
10
5
25
20
H 1 h
0-30 cm
B^a-o^88^ " d-o^s-H 1 1 r
30-60 cm
60-90cm
\ 1 h
OtO-B-iP-
0 300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig 31 Soil mineral nitrogen concentration at different depths, sampling locations, and under three
cropping systems Cropping systems, levels of N supply, and sampling locations are explained in
Matenals and Methods Values are averages over levels of N supply for the locations A, and C are
averages of 1991 to 1993, those for location B are means of 1992 and 1993
87
A B
cc
LGM/Chem
LGM/Mech - -
-\ 1 1 h
\ h
1 r
0-90 cm c
^rn0-30 cm
£=H=3-30-60 cm
60-90 cm
n-rffc-BrB
NllO
°fVn
0 300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig. 32. Soil mineral nitrogen concentration at different depths, sampling locations, and under three
cropping systems with NllO. For further information see Fig. 31.
0 300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig. 33. Soil mineral nitrogen concentration at different depths, sampling locations, and under three
cropping systems with N250. For further information see Fig. 31.
89
1992, and 1993 are shown, while for the location B (sampling 19 cm from the maize
rows), the average of 1992 to 1993 only is shown. This must be considered when
comparisons between sampling locations are made.
Under CC, the Nmin concentration (0 to 90 cm depth) was higher than that in
the LGM plots from the 6th leaf stage onwards at location A and from the first sampling
date onwards (= 3rd leaf stage) at locations B and C (Fig. 31). Under LGM/Chem, the
Nmin concentration at location A tended to be higher than that in the LGM/Mech plots
(Figs 31,32, and 33), especially from the 9th leaf stage onwards with N250. In contrast,
at the locations B and C, the Nmin concentrations under LGM/Chem and LGM/Mech
plots were similar, irrespective of the level of N supply (N110 and N250). At pollen
shedding, the Nmin concentration at location A was similar with Nl 10 and N250 in all
cropping systems (Figs 31 to 33).
In the top soil (0 to 30 cm depth) and at location A, LGM systems had 40 mg and CC
33 mg of mineral N kg"1 dry soil at the 3rd leaf stage (Fig. 31). Thereafter, with Nl 10
(Fig. 32), the differences between the CC and the LGM systems were small until silage
maturity. It seems, however, that the LGM/Mech plots showed greater reductions in the
Nmin concentration than the LGM/Chem and the CC plots. At locations B and C, the
Nmin concentrations were higher under CC than under the LGM systems from the 3rd
leaf stage until the 9th leaf stage. In the sub soil layers (at depths of 30 to 60 cm and
60 to 90 cm), there were higher Nmin concentrations in the CC system than in the LGM
systems from the first sampling date until pollen shedding, independent of sampling
location. There were no great variations between the LGM systems throughout the
growing season, irrespective of the sampling location and the soil layer. With the
exception of location A at depths 30 to 60 cm, LGM/Chem tended to have higher Nmin
concentrations than LGM/Mech until the 9th leaf stage. With N250 (Fig. 33), the
variations between the cropping systems at location A and in the top soil were greater
than with Nl 10. The Nmin concentration in the LGM/Chem and CC plots peaked at the
9th leaf stage, whereas under LGM/Mech it decreased during the whole growing period.
In the sub soil layers and for the same location, LGM/Mech showed the lowest Nmin
values throughout the growing period. At the locations B and C and in the top soil, the
CC plots had the highest Nmin concentrations until the 9th leaf stage, whereas in the
sub soil layers, differences between the CC and the LGM systems persisted until silage
maturity. The Nmin concentrations in the LGM/Chem plots tended to be higher than
those in the LGM/Mech plots, especially in the sub soil layers.
90
40
30
20
10
80
60
'8 40
>2060
E25
20
15
10
5
25
20
15
10
5
0
1 1 r
0-90 cm
H 1 h
0-30 cm
—H 1 h
30-60 cm
- 60-90 cm
Growing degree days [°C d]
40
30
20
10
80
60
40
20
25
20
15 h
10
5h
25
20
15 h
10
5
0
cc
LGM/Chem
LGM/Mech
\ 1 1—
NllO
H 1 \
Growing degree days [°C d]
Fig. 34. Soil mineral nitrogen concentration (NllO in 1991) at different depths, sampling locations,
and under three cropping systems. For further information see Fig 31.
91
Growing degree days [°C d]
40
30
20
10
80
60
40
20
25
20
15
10
5
25
20
15
10
c
i r
0-90 cm
cc
LGM/Chem -
LGM/Mech
0-30 cm
1 h
30-60 cm -
60-90 cm
Growing degree days [°C d]
Fig. 35. Soil mineral nitrogen concentration (N250 in 1991) at different depths, sampling locations,
and under three cropping systems. For further information see Fig. 31.
92
0 300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig 36 Soil mineral nitrogen concentration (NllO in 1992) at different depths, sampling locations,and under four cropping systems For further information see Fig 31
93
t 1 r
0-90 cm
i 1 1 r
:: N250
B
^\ 1 h \ 1 h
0-30 cm
30-60 cm CC
LGM/Chem
LGM/Mech
DGM
60-90 cm
i&££=i=*0 300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig 37 Soil mineral nitrogen concentration (N250 in 1992) at different depths, sampling locations,
and under four cropping systems For further information see Fig 31
94
*u 1 I
• 0-90 cm
1 1
A'
30 -
20 - -
10 -
80V«4.
1 1
• 0-30 cm •
60 -
1 40 _
dry •
-j 20
- 25•W-T""8!
1 1 1 1eo
°a 20'_ 30-60 cm
-
10 i -
5 V25
°T^*-=T^*ii r 1 1
20^ 60-90 cm
-
15 -
10 - -
5
na^^SSp^, "
40
30
20
10
80
60
40
20
25
20
15
10
5
25
20 -
15 -
10
5
0
1 1 r
c- cc
- LGM/Chem
- LGM/Mech
- LCM/Mech
NO
Growing degree days [°C d] Growing degree days [°C d]
Fig. 38. Soil mineral nitrogen concentration (NO in 1993) at different depths, sampling locations, and
under four cropping systems For further information see Fig 31
95
40
30
20
10
80
60
• A
1 40
dry'an 20M
so
a25
u8Oo 7,0
P7,
15
10
5
25
20
15
10
5
0
i i i r
B 0-90 cm I CCC
LGM/Chem
LGM/Mech
LCM/Mech'
T-^r-
0-30 cm
=F=*-
30-60 cm
60-90 cm
n 1 1 r
NllO
F-=l-
0 300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig 39 Soil mineral nitrogen concentration (NllO in 1993) at different depths, sampling locauons,
and under four cropping systems (no values for LCM at location B exist) For further mformauon
see Fig 31
96
0 300 600 900 1200 300 600 900 1200 300 600 900 1200
Growing degree days [°C d]
Fig 40 Soil mineral nitrogen concentration (N250 in 1993) at different depths, sampling locations,and under three cropping systems For further information see Fig 31
97
Averaged across the levels of N supply, DGM plots had relatively higher Nmin
values (0 to 90 cm depth) than the CC, LGM/Chem, and LGM/Mech plots (DGM, 26.0,
CC, 22.2; LGM/Chem 18.55; and LGM/Mech, 24.1 mg of mineral N kg"1 dry soil) at
the 3rd leaf stage (Figs 36 and 37). Afterwards, with Nl 10, the Nmin concentration at
location A was still higher in the DGM system than in all other cropping systems until
pollen shedding (Fig. 36). With N250, however, the DGM and CC plots showed similar
Nmin concentrations during the rest of the growing season (Fig. 37). At the locations
B and C, the Nmin concentrations in the DGM system were between those in the CC
and LGM systems with both levels of N supply (Figs 36 and 37).
On unfertilized plots (NO), only the Nmin concentration (0 to 90 cm depth) under
CC decreased during maize development, whereas in the living mulch systems (LGM
and LCM), the Nmin concentrations were always very low, irrespective of the sampling
location (Fig. 38). At the 9th leaf stage, all cropping systems had about the same Nmin
concentration. At location A, Nmin values in the 0 to 30 cm layer were higher on the
CC plots than on the living mulch plots until the 6th leaf stage. In the 30 to 60 cm
layer, they were higher until the 9th leaf stage, and in the 60 to 90 cm layer, they were
higher until pollen shedding. At location C, CC plots showed higher Nmin values than
LGM/Chem, LGM/Mech, and LCM/Mech plots until the 9th leaf stage in the 0 to 30
cm and the 30 to 60 cm layers, and until pollen shedding in the 60 to 90 cm layer. In
the 0 to 30 cm layer, no differences were observed between LGM/Chem, LGM/Mech,
and LCM/Mech at any location throughout the maize growing period (data for
LCM/Mech at the 3rd leaf stage are not available). At the A and C locations, the Nmin
concentrations were slightly higher on LCM/Mech plots than on LGM plots until the 9th
leaf stage in the 30 to 60 cm layer and until the pollen shedding in the 60 to 90 cm
layer.
With Nl 10, the LCM systems had clearly higher Nmin concentrations at the
location A (0 to 90 cm depth) than all other cropping systems until the 6th leaf stage
(Fig. 39). The LCM/Mech system showed temporal patterns in the Nmin concentration
at location C which were similar to those under NO in all soil layers (Fig. 38). The
Nmin concentration at location A was higher on the LCM/Mech plots than on the CC
and LGM plots until the 6th leaf stage in the top soil and at the 3rd leaf stage in the sub
soil layers (Fig. 39). Thereafter, the Nmin concentrations in the sub soil layers of the
LCM/Mech system were similar to those of the CC plots.
6.2.3 Nmin concentration one month after maize harvest
Nmin concentrations (0 to 90 cm depth) one month after the maize harvests in
98
30
3 20
1 10
A C
\tk
91
^M cc
I I LGM/Chem
Y77A LGM/Mech
E38 DGM
th WkNllO N250 NllO N250
NllO N250 NllO N250 NllO N250
Fig. 41. Soil mineral nitrogen concentration (0 to 90 cm depth) at different, sampling locations,and under various cropping systems one month after maize harvest. Bars are LSD (0.05) values.
For further information see Fig. 31.
1991 and 1992 are shown in Fig. 41. The CC plots had higher Nmin concentrations than
LGM/Chem and LGM/Mech at all sampling locations under both Nl 10 and N250 and
in both years with one exception only (1991, location A, N250). In 1991, LGM/Chem
had higher Nmin concentrations than LGM/Mech at the locations A and C with both
levels of N supply. In 1992, values were generally lower. LGM systems were the same
with N250, whereas with NllO, the LGM/Chem plots tended to have higher Nmin
values than the LGM/Mech plots at all sampling locations. The CC and DGM systems
had similar Nmin concentrations.
99
6.3 Discussion and conclusions
6.3.1 Cover crop effects on Nmin content before maize sowing
Different dates of ryegrass harvest in autumn and the year to year variations in
the environmental conditions during the cool season (Figs 1 and 2) may have greatly
influenced the DMA and NA of ryegrass and the amount and distribution of Nmin in
the soil in March and at the ryegrass cutting in spring (Table 15). The results presented
in this chapter demonstrate that Italian ryegrass was quite efficient in depleting the Nmin
pool of the soil, thus reducing the nitrate leaching hazard during the cool season. Before
maize sowing, averaged across the years, ryegrass plots had only 26% (19 kg N ha"1)
of the Nmin content (0 to 90 cm depth) of the ploughed plots (74 kg N ha"1). Low Nmin
contents of soil under ryegrass stands in spring have also been reported by Bergstrom
(1986) and Alvenjis and Marstorp (1993). Stubble incorporation (Andersen and Olsen,
1993) and ploughing have been reported to stimulate the mineralization of N (Goss et
al., 1988). Cameron and Wild (1984) estimated that the amount of nitrate leached over
winter below 90 cm may be as high as 100 kg N ha"1 as a result of ploughing the
grassland. Therefore, it is possible that some Nmin, released after ploughing the plots,
was allocated to the sub soil and, thereafter, partially leached during the cool season.
Addiscott et al. (1991) reported that cover crops vary in N uptake efficiency and rate of
decomposition after incorporation in the soil. In the present study, the CC system
included a ryegrass cover crop whose stubble was ploughed under in autumn/winter
period. Ploughing and incorporation of organic matter may have increased the release
of N during the cool season and during the maize cropping period on the CC plots. It
must be born in mind, however, that the CC treatment is not typical of conventional
maize cropping in Switzerland, where farmers do not usually include an autumn cover
crop.
The effect of the ryegrass on the Nmin content was already detected on the first
sampling date (mid March); at this sampling, the Nmin values under the ryegrass stands
were only one third (21 kg N ha"1) of those found for the ploughed plots (66 kg N ha"1).
Of the 52 kg N ha"1 accumulated in the biomass of Italian ryegrass at the spring cutting,
70% (e.g. 38 kg N ha"1) was already present in the ryegrass in March (Table 15). Thus,
ryegrass absorbed the bulk of its N during the autumn/winter period. In agreement with
this Thorup-Kristensen (1993b) found that winter cover crops absorb most of their N
from the autumn soil Nmin pool.
In the present study, the Nmin pool of the soil was almost depleted by early
spring (mid March) on ryegrass plots as compared to the ploughed plots (Tables 15 and
16). In line with this Thorup-Kristensen (1993a) reported that, after overwintering,
Italian ryegrass left the sub soil essentially without Nmin. This explains why the
100
increment in NA between the first (mid March) and second spring ryegrass sampling
was low (14 kg N ha"1). The variation in the Nmin content of the soil during spring (mid
March until the spring cutting of ryegrass) was small, indicating that, under ryegrass
stands, N mineralization and N uptake by the ryegrass were in equilibrium. More Nmin
generally disappeared from the sub soil layers (30 to 60 cm and 60 to 90 cm) than from
the top soil (Table 16).
An opposite effect was detected under the ploughed plots; increments in the
Nmin content of 8 kg N ha"1 were found in the period between the first and the second
samplings in spring (Table 15). Table 16 shows that, of the Nmin increment in spring,
62% (5 kg N ha"1) was detected in the sub soil layers. This indicates an appreciably
greater nitrate leaching hazard under ploughed plots than under plots planted with Italian
ryegrass. Because mineralization of organic matter is related to soil temperature
(Stanford et al., 1973) and moisture (Smith et al., 1977), mineralization rates of organic
residues increase with increasing soil temperature during the spring (Cassman and
Munns, 1980). This may influence the Nmin content of the soil, especially under the
presumably well aerated ploughed plots, where the ryegrass stubble decomposed, thus,
enhancing the N mineralization (Jackson et al., 1993). As a result, the risk of nitrate
leaching on CC plots was still present during the early stages of maize development. In
contrast on the LGM plots, the ryegrass strips removed plant available Nmin from the
soil.
There are other factors which may have contributed to the low Nmin content
found under ryegrass stands in spring. It is possible that, under cover crops, N
mineralization rates were lower than those in ploughed soils (Alvenas and Marstorp,
1993), because tillage enhances N mineralization. Furthermore, during cool and wet
periods, losses of N through denitrification may be high, because the root system of the
cover crop partially reoccupies the soil pore system which may reduce the drainage of
water (Smucker and Richner, 1995) and decrease the 02 supply in the top soil.
Furthermore, the release of soluble C (Jarvis, 1992) from cover crop roots and the
mineralization of decaying plant residues may stimulate the microbial respiration,
thereby reducing the availability of 02 in the soil (Drury et al., 1991). The presence of
easily decomposable sources of C as well as anaerobic conditions may trigger
denitrification processes. It is possible, therefore, that denitrification was more intensive
under ryegrass stands than on plough-tilled land during the cool season. The cover crop
species may also have an effect on the Nmin content in spring. In 1993, the Nmin
content was 20 kg ha"1 under white clover stands, whereas it was only 11 kg N ha"1
under ryegrass stands (Table 4, chapter 2). Ilgen (1990) found that, as compared to
fallow fields, non-legume cover crops reduced the nitrate content of the soil by about
75%, whereas legume cover crops reduced it by approximately 50%. Thorup-Kristensen
101
(1993a) reported that deeply rooting cover crops, which build up their root system very
fast, are especially efficient in removing potentially leachable N from the soil.
6.3.2 Effect of the mulch seeding systems on the Nmin concentration
In all cropping systems, a strip 30 cm wide was tilled to prepare the seedbed for
maize. During the tillage operation, living ryegrass stubble, living clover, or residues of
ryegrass killed by herbicide were incorporated into the soil and mixed with the soil to
a depth of 15 cm. Various soil factors and the type of plant residues may have affected
the release of Nmin and its availability to maize. The C/N ratio of the cover crop
residues indicates the rapidity with which N may be released after it is incorporated into
the soil (Das et al., 1993). However, cover crop residues with similar C/N ratios may
show different decomposition rates (Somda et al., 1991). Investigations, by Herman et
al. (1977) indicated that, apart from the C/N ratio, the lignin/carbohydrate ratio affects
the mineralization of N. In the present study, the C/N ratio of the various cover crops
residues was not measured. It is noteworthy, however, that in the tilled strips and with
Nl 10, higher Nmin concentrations (0 to 30 cm and 30 to 60 cm layers) occurred in the
LCM/Mech system than in the LGM systems at early stages of development (Fig. 38).
Unfortunately, no samples were taken at the 3rd leaf stage on the unfertilized
LCM/Mech plots (Fig. 39). Somda et al. (1991) reported that residues with low initial
C/N ratios (e.g. legumes) generally decompose more rapidly (e.g. within the 14 days)
than residues with high initial C/N ratios (e.g non-legumes). Breland (1989), cited by
Andersen and Olsen, (1993) reported that the release of N from ryegrass required an
incubation period of 180 days and that, during the first 53 days, a complete im¬
mobilization occurred. Thus, it is possible that in the present study the incorporation of
the ryegrass stubble caused immobilization of N, which may account for the low Nmin
content under the tilled strips of the LGM systems.
In the DGM system, the Italian ryegrass was killed four weeks prior to maize
sowing (Figs 36 and 37). It is suggested, therefore, that N released from the dead plant
material became available to the subsequent maize crop, as indicated by the fact that on
the DGM plots and with Nl 10, the concentration of Nmin (0 to 90 cm depth) under the
maize rows was higher than on the LGM plots, especially at the 3rd leaf stage. With
N250, the differences between the DGM and LGM systems were smaller. Wagger
(1989) reported that desiccated cover crop residues decomposed relatively fast. It has
to kept in mind, however, that the rates of additional fertilizer N application, carried out
at sowing, were the same for the DGM and LGM systems (Table 4). Because the Nmin
content in the soil prior to maize sowing was not determined for the DGM system it
cannot be excluded that the higher Nmin concentration under DGM plots in the tilled
strip resulted from the mineralization of the buried residues at maize sowing. In fact, the
102
Nmin concentration between the rows (0 to 90 cm depth) was also higher for DGM than
for LGM plots. This may suggest that some Nmin was released from the residues of the
cover crop (Figs 36 and 37). The reason why Nmin concentrations (0 to 90 cm depth)
between the maize rows (locations B and C) were slightly higher for LCM/Mech than
for LGM plots is unclear (Figs 38 and 39). Reduced N uptake by the clover crop,
fixation of atmospheric N, and mineralization of clover residues may have contributed
to this phenomenon.
6.3.3 Effect of N placement and tillage
The use of cover crops may help to alleviate the leaching of nitrate into the
groundwater (Drury et al., 1991). However, cover crops may initiate a pre-emptive
competition for N (Thorup-Kristensen, 1993b) which may adversely affect the growth
of the following main crop, e.g. maize. The negative effect of the cover crop will be
even greater if the cover crop is harvested instead of being incorporated into the soil or
left on the soil surface as dead mulch (Moschler et al., 1967). Doran et al. (1989)
reported that the N supply to minimum tillage maize in combination with cover crops
can be increased by incorporating the cover crops early. Due to the low Nmin content
under the LGM systems, additional N fertilization was necessary in order to compensate
for the relatively low Nmin concentrations in the soil. Averaged across the years, an
additional 56 kg N ha"1 was applied to LGM systems (Table 4). The N fertilizer was
applied to the rows. According to Burns (1991), application of N to the rows affects the
availability, distribution, and ttius the positional availability of the Nmin in the soil. This
may influence growth of shoots (Kovar, 1992), root morphology (Shaviv and Hagin,
1991), and N uptake of the main crop (Maidl, 1990). In part, variations in the Nmin
concentration at the various sampling locations resulted from N banding. Higher Nmin
concentrations (0 to 90 cm depth) at location A (= sampling in the maize rows) than at
the locations B (= sampling 19 cm from the maize rows) and C (= sampling 38 cm from
the maize rows) were found, especially at early stages of maize development (Figs 31
to 33). However, when no N fertilizer was applied (Fig. 38), similar Nmin con¬
centrations were found in the row and between the rows throughout maize development.
Thus, the spatial distribution of Nmin under fertilized plots was characterized by Nmin
concentrations that decreased with increasing sampling depth and increasing distance
from the maize rows (Figs 31 to 33). This was especially true for high levels of N
application (N250), irrespective of the cropping system.
In the LGM plots, the additional N fertilizer application at maize sowing
(averaged across the years = 56 kg N ha"1) surely contributed to the high Nmin
concentrations in the top soil (0 to 30 cm depth) at location A at the 3rd leaf stage as
compared to the CC plots (Figs 31 to 33). This may explain why both DM formation
103
and N accumulation of maize (Figs 12 to 17) were similar or even higher for LGM
maize than for CC maize, even though the LGM plots had lower Nmin concentrations
between the rows (locations B and C) and in the sub soil of location A than the CC
plots on this sampling date (Figs 31 to 33). This means that maize grown on LGM plots
relied mainly on N applied to the maize rows at sowing. This view is supported by the
observation that dry weather conditions (Fig. 2) at early stages of maize development,
as found in 1992, were associated with reduced growth of LGM maize. This was
probably due to the positional unavailability of fertilizer N (Figs 36 and 37). Additional
evidence of the reliance of fertilizer N applied to the rows is that DM formation, N
accumulation, and the plant N status were lower for LGM maize than for CC maize
(Figs 12 to 20 and 27).
With Nl 10 and in the maize rows, greater amounts of Nmin disappeared from
the top soil of the LGM plots than from the top soil of the CC plots between the 3rd
and 6th leaf stage (Fig. 32). Afterwards, only small differences between the cropping
systems were detected until silage maturity. Under N250, the Nmin concentration (0 to
30 cm depth) in the maize rows was markedly higher for CC than for LGM systems
after N fertilization at the 4th and 6th leaf stages (Fig. 33). This is probably due to the
fact that ryegrass removed N from the tilled strips. This view is supported by the
observation that the Nmin values were higher under LGM/Chem than under LGM/Mech,
i.e. in the system where the ryegrass was killed. This was found especially with N250.
As a result of the relatively high availability of Nmin, the plant N status, DM formation,
and N accumulation of maize were higher for LGM/Chem than for LGM/Mech (Figs
12 to 21 and 27 to 28), irrespective of the amount of N fertilizer applied.
Hiitsch and Mengel (1992) reported that changes in soil cultivation methods may
affect the Nmin distribution in the soil profile. For example, it has been shown that
ploughing the soil may stimulate the mineralization of N (Lai, 1995). In contrast, no-
tillage and minimum tillage reduce the release of N (Angle et al., 1993). At locations
B and C, in all soil layers investigated, the CC plots showed clearly higher Nmin
concentrations than those of all mulch seeding systems at early stages of maize
development (Figs 31 to 40). This is probably due to autumn ploughing (Figs 31 to 40).
Such conditions may have favored the N uptake of maize on the CC plots and, thus, also
enhanced the DM formation and N accumulation (Figs 12 to 21 and 27 and 28) than in
the mulch seeding systems, irrespective of the level of N supply.
It is clear that the high Nmin values, as found under CC, increase the nitrate
leaching hazard not only before maize sowing (Table 16) but also during maize
development (Fig. 31) and after the harvest of maize (Fig. 41). The nitrate leaching
hazard from the DGM plots, during the maize development, is between the CC and the
LGM plots (Figs 36 to 37) and also after the maize harvest (Fig. 41). In the LGM
104
systems, the risk of nitrate leaching is only postponed during the cropping period (Table
16 and Figs 31 to 41); leaching of nitrate may occur after tillage operations which
disturb and aerate the soil, because organically bound N can be mineralized then. The
soil nitrate leaching hazard of the LCM systems ranked between the CC and LGM
systems (Figs 38 to 39).
105
7 GENERAL CONCLUSIONS
The following conclusions can be drawn from the experiments:
i) In comparing the economical returns from the different maize cropping systems,
it has to be taken into account that short-term cost analyses do not consider the
soil and water conservation values under reduce tillage systems. Since soil
erosion is a serious problem to long-term sustainable crop production in
Switzerland, and the nitrate contamination of drinking water is a matter of public
concern, productions systems that employ cover crops are subsidized in some
regions. This is a further stimulus for continuing research on environmentally
sound croppping systems.
ii) The Italian ryegrass cover crop markedly reduces the nitrate leaching hazard
during the cool season and during the seedling stage of maize, but it reduces the
availability ofN to the maize crop and may postpone the risk ofN leaching after
the maize harvest. Furthermore, Italian ryegrass is not an ideal living mulch for
maize, because large amounts of N fertilizer are required to reach the dry matter
and N yields of plough-tilled maize.
iii) With the objective of improving the production recomendations, changes in the
botanical composition of the winter cover crop and in the manner in which the
cover crop is regulated could help to reduce the N requirements and increase the
economical returns from living mulch systems.
iv) Killing the Italian ryegrass four weeks before sowing results in dry matter and
N yields similar to those of conventionally cropped maize. This required,
however, an additional input of N fertilizer and pesticides.
v) Application of N fertilizer to the maize rows is an integral part of proper N
fertilizer management for maize production in living grass mulches in order to
minimize competition.
vi) Research efforts to optimize the beneficial environmental effects of living mulch
systems should focus on further reduction of the competition of maize and the
cover crop for N. Competition experiments may help to elucidate interactions
between the living mulch and the main crop and to develop or select less
106
aggressive cover crop ideotypes; possible candidates may be legumes (e.g. white
clover, red clover), grass-legume mixtures, and grasses (e.g. turf-type perennial
grasses). However, the economical advantage of a preharvest could be lost.
vii) Perspectives to be evaluated for further optimization are offered by diverge
modifications like broader tilled strips, narrower spaces between the rows of
maize, and varieties with high early vigor, fast leaf developoment, and large leaf
area.
107
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Acknowledgements
I would like to express my thanks to Prof. Dr. Peter Stamp for giving me the
opportunity to carry out this work in his group and for his support and understanding
during the course of this doctoral work.
I am especially grateful to PD Dr. Boy Feil for contributing many ideas, fruitful
criticism, for the thorough revision of the manuscript, and for his friendship.
I wish to express my sincere gratitude to Dr. H.U. Ammon for his support of the field
and laboratory work and for his scientific, personal advice and his friendship.
My thanks go to Christian Bohren for assistance with the field work, to Caroline
Scherrer for many hours of hard field work, and for plant and soil sampling, and to
Hubert Biirgi for his help in soil sampling.
My thanks also go to the staff of FAL Reckenholz. The time I spent at this institution
was very satisfactory from a scientific point of view, and I also enjoyed the company
of my colleagaes. I would like to thank Marcia Schonenberg for checking the English
manuscript.
I thank all my colleagues at the Institute of Plant Sciences, especially those in the group
for arable crops and plant breeding, for their help, support, and friendship.
Curriculum Vitae
December 14, 1962 Born to Salvador Garibay Arroyo and Elizabeth Kuri Cano
in Coalcoman, Michoacan, Mexico.
1969 - 1975 Primary school in Guadalajara, Jalisco.
1975 - 1978 Secondary school in Guadalajara, Jalisco.
1978 - 1981 Grammar school in Guadalajara, Jalisco.
1981 - 1986 Student at the Faculty of Agriculture of the University of
Guadalajara (UdeG), Jalisco, Mexico.
1982 - 1985 Jardines y Viveros Colonia Seattle, S.A. Guadalajara, Jalisco,Mexico.
1986 Farm "Los Leones," Autlan de Navarro, Jalisco, Mexico.
1986 - 1988 Sunnyside Nurseries Inc. Hayward, California, USA.
1988 Diploma in Agronomy; Thesis: Enraizamiento de hijuelos enviveros de Agave Azul Tequilero (Agave tequilana W.)utilizando hormonas.
1989 Practical training at the Arbeitsgemeinschaft Beratender
Agronomen (Agba AG), Ebikon.
Practical training at Pliiss-Staufer AG/Agro, Oftringen.
Hallerplanzen Rufenach A.G., Argau.
Practical training at the Swiss Federal Research Station for
Agronomy, Zurich-Reckenholz.
Practical training at the Institute of Plant Sciences of the
Swiss Federal Institute of Technology, ETH, Zurich.
Scientific collaborator at the Swiss Federal Research Station
for Agronomy, Zurich-Reckenholz.
1995 Scientific collaborator at the Swiss Federal Research Station
for Fruit-Growing, Viticulture and Horticulture.
1991 - 1996 Ph. D. student and scientific collaborator at the Institute of
Plant Sciences of the Swiss Federal Institute of Technology,ETH, Zurich.
1989- 1990
1990
1990- 1991
1991 - 1995
