AGRONOMY SECTION

Zero-tillage influence on canola, field pea and wheat in a drysubhumid region: Agronomic and physiological responses

Sylvia BorstlaP and Martin H. Entz

Department of Plant Science,IJniversity of Manitoba, Winnipeg, Manitoba, Cary!a R3T 2N2. Contributionno.944, received 7 June 1993, accepted 5 January 1994.

Borstlap, S. and Enz, M. H. 1994. Zero-tillage inlluence on canola, field pea and wheat in a dry subhumid region: Agronomicand phrysiological responses. Can. J. Plant Sii. 74: 411-420. Field trials were conducted over 4 site-years in southern Manitoba

to cornpare thl ."rponi. of Katepwa wheat, Westar canola and Victoria field pea to zero. tillage (ZT). The experimental design

was a split plot with tillage systeh as the mainplot (ZT vs. conventional tillage (CT)) and crop species as the subplot. All crops

received protection frominsett, weed and diseaie pests. Tillage system had only a limited impact on crop dry matter accumulation

or grain {uality. Where differences were observed-, crop performance was enhanced under ZT. Seasonal evapotranspiration (ET)

wai either reduced or unaffected by ZT, while Ei efficiency (ETE: kg ha-1 mm-l ET) was eitherincreased or unchanged by

the shift from CT to ZT. Higher EiE under ZT was attributed to less soil water evaporation. Significant tillage system x crop

species (T x S) interactions-for growth parameters, ET and ETE indicated that field pea often benefitted more than wheat or

cinola fiom ZT. A significant T -x

S interaction at one of the four sites indicated that water extraction between 30 and 90 cm

was higher for pea and canola in the ZT compared with CT treatment, while soil water extraction by wheat was reduced under

ZT . Al a second site, lower ET for all three crops under ZT was attributed to reduced water use between 90 and 130 cm. Despite

some effects of ZT on crop growth and water use, no significant tillage, T X S, or site x tillage interactions were observed

for grain yield. It *ur "onilided

that under the conditions of this study (i.e. precipitation and temperature conditions close to

the iong-term average), Westar canola, Victoria field pea and Katepwa wheat were, for the most part, equally suited to ZT production.

Key words: Soil water extraction, evapotranspiration efficiency, crop quality, grain yield, canopy development

Borstlap, S. et Entz, M. H. 1994. Effet du semis direct sur le canola, le pois de grande crr-ltu_re et le bl€ dans une zone

subhumide sOche: rdactions agronomiques et physiologiques. Can. J. Plant Sci. 74 4ll-420. Des essais au champ ont 6t6

r6alis6s sur quatre ann6es-stations dans ie sud du Manitoba pour comparer les r6actions du bl6 cv. Katepwa, du,colza.canola

Westar et du pois de grande culture Victoria au semis direct (SD) . On utilisait un dispositif exP6rimental en parcelles divi#es 'le traitement di travaiidu sol, SD et travail classique (TC), formant les grandes parcelles et les especes cultiv6es les sous-parcelles.

Toutes les cultures recevaient un traitement de protection contre les insectes, les maladies et les mauvaises herbes. Le systbme

de travail du sol n'avait qu'un impact limit6 sui I'accumulation de la matibre sdche dans les cultures et sur la qualit6 du grain

et lorsqu'il y avait des diff6rences, I'avantage allait au SD. Le semis direct avait un effet rdducteur ou un effet nul sur l'6vapo-

transpiiation saisonnidre, tandis que |e passige de TC i SD exergait un effet accroissant ou nul sur I'efficacit6 de ET (EET:kg

ha-r'mm-t ET). La plus forte nbf oUiervee en r6gime SD s'explique par une moindre 6vaporation de I'eau du sol. Les inter-

actions significatives intre le rdgime de travail du sol et I'espbce cultiv6e (T x EC), constat6es pour les paramdtres de croissance,

pour ET Et pou. EET, indiqueit que SD profitait davantage au pois qu'aux deux autres cultures. Une interaction significativei x BC relivde ir l'un des deux emplacements porte i conclure-que l;extraction de l'eau dans la couche du sol de 30 d 99 cm

de profondeur 6tait plus forte pour le pois et pour le canola en r6gime SD qu'en TC, tandis qu'elle6tait plus.faible pour le b16-

Au second emplacement, la mbindre ET obs"*6e pour les trois cultures en r6gime SD 6tait reli6e ir une moindre utilisation de

I'eau dans la couche de 90-130 cm. Malgr6 quelques effets de SD sur la croissance et sur I'utilisation de l'eau, on ne notait

aucune interaction significative T x EC ou emplaiement X r6gime de travail du sol pour le rendement grainier. Les auteurs

concluent que, dans i-es conditions oi s'est d6roul6e I'exp6rience, c'est-il-dire pr6cipitations et temp6rature assez voisines de la

moyenne i iong terme, les trois espdces 6tudi6es possedaient dans I'ensemble des aptitudes comparables )r la culture en semis direct.

Mots cl6s: Extraction de I'eau du sol, efhcacit6 de l'6vapotranspiration, qualit6 de la r6colte, rendement en grain, ddveloppement

du couvert

The zero tillage (ZT) crop production system provides many either similar or higher under ZT than conventional tillage

important benifits such ai reduced soil erosion-, lower energy (CT). Differences in the way crops responded- to ZT inconsumption in crop production, and improved moisture previous studies could often be attributed to differences in

conservition and use efficiency (Unger t990;. While there moisture conditions, with ZT crops performing betterin dry

is a grear deal of interest in Zt among crop producers in years(Webberetal. 1987;WolfandEdmisten1989)'Inwetthe elstern prairies, only a limited amount bf information years, emergence under ZT may be slower and plants may

exists on how ZT affects productivity of different crops in be more susceptible to diseases such as common root rot

the region. (Cochliobolus sativus) (Klepper and Rickman 1988).

Previous research indicarcd that yields of wheat (kiticumaestiwm L.) (Donaghy 193; Wilhelm et al. D89; lafond et al.

W2), carrcla (Brassica napus L.) (Donaghy 193; Wright D89)and field pe* (Pisum satiwm L.) (Lafond et al. 1992) *"r"

o,

Abbreviations: CT, conventional tillage; DM, dry matter;ET, evapotranspiration; ETE, evapotranspiration efhciency ;

ZT. zero tillage

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412 CANADIAN JOURNAL OF PLANT SCIENCE

In western Canada, the absence of preseeding tillage oftenresults in lower soil temperatures (Gauer et al. 1982; Walland Stobbe 1984; Carter and Rennie 1985) and higher levelsof available soil water (Gauer et al. 1982: Lafond et al.1992). It is important to note that while changes in the soilenvironment under ZT can influence crop productivity,environmental factors such as precipitation and air tempera-ture can modify crop response to tillage (Wright 1989).

Few studies in western Canada have considered the effectsof ZT on growth processes such as dry matter accumulation,canopy development, root activity and evapotranspirationefficiency. Information is especially lacking for canolaand field pea. Working in Nebraska, Doran et al. (1984)observed more rapid canopy closure with corn (Zea maysL.) and soybeans (Glycine maxL.) under ZT than under CT,while Wilhelm et al. (1989) reported a lower leaf area indexfor winter wheat under ZT than CT. Under late-seasondrought conditions in southern Saskatchewan, Campbellet al. (1986) observed (visual observations only) a 2-wk delayin leaf senescence for spring wheat grown under ZTcompared with CT.

Both dry matter production and seed yield in wheat (Entzand Fowler 1989), canola (Clarke and Simpson 1978), andfield pea (Wilson et al. 1985) are closely related to seasonalevapotranspiration (ET). Seasonal ET can be influenced bytillage system in a number of different ways. ZT may increaseET by increasing the amount of water available for cropgrowth (Lafond et al. 1992), or by increasing crop growthdue to other factors (Webber et al. 1987). On the other hand,ZT can reduce root exploration of soil due to delayed growthin spring (Klepper and Rickman 1988) and a smaller rootsystem (Chevalier and Ciha 1986; Varvel et al. 1989). Whilesome information on the effects of ZT on soil water extractionor root growth is available for wheat, the effects of ZT onroot activity in canola or pea do not appear to have beenpreviously described. Higher ET efficiency (yield per unitET) under ZT has been observed by many previous workers.Pierce and Rice (1988) suggested that efficiency of wateruse in cropping systems be evaluated on the basis of twoparameters, physiological eff,rciency and recovery efficiency.

Few data are available regarding the effects of tillagesystem on crop quality. Donaghy (1973) found no signifi-cant effect of ZT on crop test weight of canola. The effectof ZT on canola oil content does not appear to have beenpreviously described; however, Deibert (1989) found thatZT had no effect on the oil content or oil yield of sunflower.

Southern Manitoba is a highly productive crop productionarea with an average moisture limitation for wheat of only25 mm (Ash et al. 1991). Crop management systems in thisarea are more intensive than in most other areas of theCanadian prairies. Spring wheat, field pea and canola areroutinely grown on cereal stubble in a continuous croppingsystem. Few previous tillage studies conducted in this drysubhumid region have compared the response of differentcrops in the same study. Such an approach is required ifstatistical comparisons between crops in a ZT rotation areto be made. Also, no previous studies in this region havemonitored the impact of tillage on physiological parameterssuch as crop canopy development and water use efficiency.

Therefore, the objective of this study was to investigate thecomparative response of Katepwa wheat, Westar canola andVictoria field pea to ZT. Such information is important forrotation planning in conservation tillage systems in the moistBlack soil zone of western Canada.

MATERIALS AND METHODSField plots were established on an Almasippi loamy very ltnesand at Carman and on a Neuhorst clay loam at Portage laPrairie (Portage), Manitoba in 1989 and 1990. The trial atCarman in 1990 and trials at Portage in 1989 and 1990 wereon long-term ZT fields (ZT for at least 5 yr). The previouscrop in 1989 trials was wheat, while the previous crop in1990 trials was barley. The experimental design was a splitplot with tillage (ZT and CT) as the main plot and cropspecies (Westar canola, Victoria field pea, and Katepwawheat) as the subplot. CT treatments consisted of two passes

in fall (in opposite directions) with a double disc, and a lightcultivation, harrowing and packing (immediately prior toseeding) in spring. CT treatments were initiated the year ofthe study in 1989 and the year prior to the study in 1990.Experiments at Carman were replicated six times whileexperiments at Portage were replicated four times. Subplotsize was 4.3 x 7 m at Portage in 1989 and 6.2 x 7 m atthe remaining sites.

Trials were seeded using a Noble Model 2000 hoe drillat 1 cm depth for canola and 2.5 cm for held pea and wheat.A 20-cm row spacing was used. The seeding depth wasadjusted separately for theZT and CT plots in order to ensurea similar seeding depth for each crop. Recommended seedingrates were used in all trials:200 viable seeds m-'forcanola, 130 viable seeds m-2 for field pea, and 300 viableseeds m-' for wheat (Anonymous 1988). In 1989, seedingwas done on 11 May at Carman and on 16 May at Portagewhile in 1990, seeding was done on 10 May at Carman andon 31 May at Portage.

Fertilizer was applied according to soil test recommenda-tions for moist conditions (Department of Soil Science,University of Manitoba). Seed-placed fertilization was thesame for all three crops in both years: 20 kg ha-t P2O5. and5 kg ha-'. nitrogen (N). An adiitional 100 kg ha-' N,70 kg ha-' K2O, and 20 kg ha-' SOa was broadcast afterseeding each year at Carman, while an additional 75 kgha-' N was broadcast each year at Portage. Weeds andinsects were controlled using pesticides at recommendedrates. Preventative disease control measures were followed,including the use of seed treatments for the control of seed-ling diseases and the use of foliar fungicides for the controlof leaf diseases in wheat (propiconazole) and canola(benomyl). Field pea seed was inoculated with Rhizobiumspp. immediately prior to seeding.

Crop residue cwer (%) for each tillage treatrnent was deter-mined using the line transect method as described by Richardset al. (1984). levels of surface residue cover immediately afterseeding for ZT and CT were 62 and,42% at Carman in 1989,

81 and 36% for Portage in 1989, 88 and 27% in Carman inl99O and 76 and20% for Portage in 1990.

Growing season precipitation was monitored at all sites.Daily maximum, minimum and mean air temperatures were

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BORSTLAP AND ENTZ - CROP RESPO'VSE TO ZERO.TILLAGE 413

recorded at the Portage site only (distance between Carmanand Portage: 60 km). Daily maximum, minimum and meantemperatures were monitored at the lO-cm soil depth at allsites except Carman in 1989 using Campbell Scientific ModelCR-10 dataloggers equipped with Model 107 temperaturesensors (Campbell Scientific Inc., Logan, UT).

Crop establishment (plant population density after fullemergence) was determined by counting the number of plants

in three adjacent l-m sections ofrow in each subplot 2-3 wkafter seeding. Crop growth was determined by measuringdry matter accumulation and plant height. Aerial dry matteraccumulation was determined at 1- to 2-wk intervals in 1989

and at 2-wk intervals in 1990. Plant material from threeadjacent, randomly selected, l-m sections ofrow from each

subplot was harvested, dried at 80'C for 48 h, and weighed.Crop height was determined by measuring the height of fourrandomly selected plants in each subplot. Crop canopy lightinterception (a measure of canopy development) was deter-mined using a Licor Model LI-185B quantum meter with a

line quantum sensor (1 m long). Measurements were takenat solar noon; the quantum flux (pE m-'s-') was deter-mined by placing the sensor at ground level beneath the cropcanopy perpendicular to the crop rows. A second readingwas taken above the crop canopy at the same orientation tosun. Percentage interception of photosynthetically activeradiation by the crop canopy was then calculated. Two sets

of light interception readings were taken per subplot.Crop development stages were determined on one repli-

cate per ffial at intervals throughout the growing season usingthe Zadoks-Chang-Kondak scale (Zadoks et al. 1974) forwheat, the Harper-Berkenkamp scale, slightly revised(Harper and Berkenkamp 1975) for canola, and the Knottscale (Knott 1987) for field pea.

Grain yield wqs determined for all subplots by harvestingan area of 10 m' in 1989 and25 m' in 1990. None of thecrops was chemically desiccated prior to harvest. Sampleswere weighed and moisture content determined using a

Labtronics Model 3.5 grain moisture meter. Yields areexpressed on a dry weight basis. Harvest index was calcu-lated as grain yield divided by total aerial dry matter.

Seed weight was determined by measuring the weight of200-1000 seeds per subplot. Pod number per plant for fieldpea and canola was determined on l0 randomly selectedplants per subplot. Plant population density at harvest wasalso determined for these crops so that the number of podsper m2 could be calculated. The number of spikes per mzof wheat was determined immediately prior to harvest onthree adjacent l-m sections of row in each subplot. Seeds

per spike or pod were calculated for all crops and sites exceptfor field pea in 1989, in which case seeds per pod werecounted on the 10 plants used for pod counts.

Protein concentration was determined from grain sub-samples for all three crops using the Kjeldahl method. Proteinyield (kg ha-') was calculated by multiplying protein contentby grain yield. Oil and chlorophyll concentration of canolawere determined using the near infrared method (Campbell1984). Oil yield (kg ha-r) was calculated by multiplyingoil concentration by grain yield. All oil and chlorophyllmeasurements were conducted at the Canadian Grain

Table l. Long-term average and actual monthly mean, minimum andmaximum air temperature at Portage la Prairie, MB, 1969 and 199t0

Temperature (oC)

Year Maximum Minimum

May

August

Averagez19891990Averager9891990Average1989r990Average19891990

18.322.r17.523.423.324.426.r31.125.425.026.726.8

11.613.9t0.217.lr6.518.019.82r.819.218.418.819.9

July

4.85.32.8

t0.79.8

I 1.5r3.515. I13.011.8lr.713.0

zlong-term (1961-1990) average air temperature at Portage la Prairie'MB; Atmospheric Environment Services, Environment Canada, Winnipeg

Climate Centre, Winnipeg, MB R3C 3V4.

Commission Oilseeds Laboratory (Winnipeg, MB). Hectolitreweights (i.e. grain bulk density) were determined using a Cox

funnel, with a top diameter of 225 mm and a bottom diameter

of 38 mm. The mass value was converted to kg hl--l.Soil water between 10 and 130 cm (20-cm increments) was

measured at spring seeding and harvest and at intervals duringthe growing season in all trials using Troxler model3222or 4300 neutron probes (Troxler Labs., Triangle Park, NC).Soil water in the 0- to 10-cm depth was determinedgravimetrically, then multiplied by soil bulk density to con-vert to volumetric basis. ET was expressed as precipitationplus soil water use between sampling dates. Runoff and deep

drainage of water was considered to be negligible' ET use

effrciency was calculated as yield (kg ha -') per unit of ET.All data, as well as all parameters calculated from the data,

were subjected to analysis of variance (SAS Institute, Inc.1986). Differences with P < 0.05 were considered tobe significant. Where combined analysis over sites wasperformed, homogeneity of error variances was first verifiedusing a maximum F test (Rohlf and Sokal 1969). Site-yearswere treated as random variables in combined analysis.

Differences between crop species were only discussed when

the tillage by species interaction was significant.

RESULTS AND DISCUSSION

Environmental ConditionsGrowing season precipitation in 1989 was 91 mm at Carman(41% of the 1961-1990 average; Environment Canada,Atmospheric Environment Service, Winnipeg, MB) and

190 mm at Portage (86% of the long-term average). The com-

bination of drought in 1988, low 1989 precipitation, and arelatively lower soil water-holding capacity, caused droughtstress to be severe at Carman in 1989. In 1990, growing season

precipitation was 220 mm at Carman (Iffi% of average) ard242 mrn at Portage (770Vo of average). For all site-years, a

large portion of the precipitation was received in June and

early July (i.e. during the critical preflowering and floweringperiods). Air temperature values for Fortage are shown inTable 1. Average and maximum air temperatures in May and

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414 CANADIAN JOURNAL OF PLANT SCIENCE

July were higher in 1989 than in 1990. Differences inprecipitation between site-years were greater than differencesin air temperature.

Soil temperatures in May and early June were 0-2oC lowerunder ZT than CT at the Portage (1989) and Carman (1990)trials (data not shown). These soil temperature differencesare similar to those reported for a 5-cm soil depth by Gaueret al. (1982). However, contrary to some previous studies(Gauer et al. 1982; Carter and Rennie 1985), lower soiltemperatures under ZT in these trials were maintainedthroughout the entire growing season. Soil temperature wasonly slightly (less than l oC) lower under ZT compared withCT at the Portage (1990) site, and differences were observedonly in the first few weeks after seeding. Soil temperaturewas not measured at Carman in 1989.

Crop Establishment and GrowthSignificant tillage effects for plant population density afterfull emergence were observed in one of the foui trials(Table 2). The significant tillage by crop species (T x S)interaction at Carman in 1990 was attributed to a positiveresponse to ZT by wheat, a negative response to ZT bycanola, and a neutral response to ZT by field pea. White andRobson (1989) found that small-seeded crops with an epigealtype of emergence, such as canola, are less able to emergeunder hard soil conditions than species with larger seeds anda hypogeous emergence mechanism.

Aerial dry matter (DM) accumulation of canola, wheat andfield pea crops is shown in Figs. l-4. The only instancewhere crop DM accumulation among crops responded differ-ently to a change in tillage system was at Carman in 1990,where a significant T x S interaction occurred on 4 June(155 DOY). (Fig. 3). Under CT, DM was 33, 104, andI 10 kg ha -' for canola, held pea, and wheat, respectively,while under ZT, DM accumulation was 49, 82, aid, 102 kgha-'-for the respective crops. A flea beetle (phyllotencruciferae Goeze) infestation appeared to cause more damageto canola under CT than under ZT, and therefore, may havebeen one reason for lower canola DM production under CT.

,G

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Fig. 1. Seasonal dry matter accumulation, canopy light intercep-tion, and crop height for crops under ZT and CT at Carman in 1989.t< and *:{< indicate significance of T and T x S interaction at the 0.05and 0.01 probability levels, respectively. DOY indicates day ofyear.

The general lack of T x S interacrions for DMaccumulation in this study indicated that, for the most part,aboveground growth was similar under ZT and CT, and that

Table 2. Plant population densitv (plants m-2) and grain yield (kg ha-l; of canola field pea and wheat grown under zero-tillage (ZT) andconventional-tillage (CT) at two locations in 1989 and 1990

Canola Field pea WheatLocation ZT ZT CT

(plants m -2)

Carman

Portage

Carman

Portage

1989199019891990

1989199019891990

2010412933713469

t962378 1

37413403

2056422130463881

58165

r02tr'7

127307268262

1807405432033880

t996227220002252

I 835218019082049

52113

t1484

63200135

135

131271248295

53106

11689

NSTxSxzNSTS

NSNSNSNS

(grain yield (kg ha-'))

Combined analysis for grain yield: Site-year**, Site-year X Species**zT x S, tillage x crop species interaction.x,x*significant ar the 0.05 and 0.01 probability levels, respectively; NS, not significant.

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BORSTLAP AND ENTZ - CROP RESPO'VSE TO ZERO.TILLAGE 415

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Fig.3. Seasonal dry matter accumulation, canopy light intercep-tion, and crop height for crops under ZT and CT at Carman in 1990.

'F and ** indicate significance of T and T x S interaction at the 0.05

and 0.01 probability levels, respectively. DOY indicates day of year.

Doran et al. (1984) attributed increased height of corn underZT to lower soil temperatures and higher levels of soil water.

Carter and Rennie (1985), on the other hand, reported a

decrease in both soil temperature and height ofwheat underZT. Zachariassen and Power (1987) reported that lower soiltemperature increased rate of nitrogen fixation in held pea,

an effect which may have increased the height of field pea

crops in the present study.Canopy light interception is an indicator ofcrop leafarea

and leaf area duration. At Poftage in 1989, ZT increasedcanopy light interception on two sampling dates in early July(Fig. 2) (i.e. around anthesis). Doran et al. (1984) observedearlier and more complete canopy closure with corn (Zea

mays L.), sorghum (Sorghum bicolor L.) and soybean whengrown under high residue compared with low residueconditions. The opposite trend was observed for the hrstsampling date at Portage in 1990 where all three crops had

a lower light interception (P < 0.05) under ZT (Fig. a).Inferior early season canopy development under ZT in thistrial may be attributed to the wetter conditions, which are

known to reduce early season plant growth and developmentrate under ZT (Klepper and Rickman 1988; Wright 1989).The absence of significant T x S interactions for canopy

Field Peo

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Fig. 2. Seasonal dry matter accumulation, canopy light intercep-tion, and crop height for crops under ZT and CT at Fortage in 1989.t< and {<* indicate significance of T and T x S interaction at the 0.05

and 0.01 probability levels, respectively. DOY indicates day ofyear.

all three crops responded similarly to a reduction in tillage.Previous workers have often observed higher DM under ZTin dry situations (Doran et al. 1984). The lack of DMenhancement under ZT at Portage in 1989 and at both sitesin 1990 was attributed to adequate amounts of precipitation.The lack of a positive tillage effect at the driest site (Carman1989) was attributed to the low level of crop residue, andthe small difference in residue level between tillage systems.

ZT significantly influenced crop height in two of the fourtrials. At Portage in 1989, signihcant T x S interactions forcrop height were recorded on four of the five sampling dates(Fig. 2). The interactions occurred because f,reld pea wasconsistently 7-12 cmtaller under ZT than under CT, whilethe height of the other two crops was unaffected. Others(Lafond and Loeppky 1988) have also observed a heightadvantage (4 cm) for f,reld pea under ZT compared with CT.In the present study, it was observed that field pea plantsgrown under ZT werc more etiolated early in the season thanthose in the CT treatments (though no light interceptiondifferences were observed between tillage systems; Fig. 2).A significant tillage effect for crop height was also observedon 4 July (185 DOY) in 1990 at Carman (Fig. 3), indicatingthat all three crops were taller under ZT compared with CT.

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113 CAHAUAH JOUNHAL OF PLANT SC'E'VCE

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o...-oe--oa-l.aloA

weight was observed only at Carman in 1990, where seedweight of freld pea was increased by 6 mg with ZT, whileseed weight of canola and wheat were unaffected by tillagesystem (data not shown).

No signihcant tillage or T x S interactions were observedfor grain yield in any of the trials in this srudy (Table 2).Upon confirmation of homogeneity of error variances, thefour site-years were analyzed in a combined analysis. Onceagain, all tillage effects, including site x tillage interactionswere found to be non-significant. Therefore, unlike otherstudies where yields of wheat (Wilhekn et al. 1989; Lafondet al. 1992), canola (Donaghy 1973; Wright 1989), and fieldpea (Lafond et al. 1992) were significantly affected by a shiftfrom CT to ZT , in this study, tillage did not affect f,rnal yieldin any of the crops tested.

Grain yield enhancement with ZT may have occurred ifconditions had been drier. The lack of a significant tillageeffect for grain yield at the driest site (Carman 1989) wasonce again attributed to the low level of previous cropresidue, and the relatively small difference in crop residuelevel between ZT and CT. Gauer et al. (1982), working ona similar soil type in the Carman, MB, area, concluded thatsoil moisture benefits of ZT were closely associated withamounts of straw cover on the soil surface. Results of thisstudy may also have been different had the wheat crops notbeen protected from leafdiseases by propiconizole treatrnent.It is also important to note that since genotypic variation forcanola (Wright 1989) and wheat (Hall and Cholick 1989)response to ZT exists, results may have been different haddifferent cultivars been used.

The lack of significant tillage effects for grain yield alsoindicates that some of the advantages of ZT recorded earlierin the season, especially for field pea, were not expressedin final yield. The absence of significant tillage effects forharvest index (data not shown) indicated that tillage regimedid not affect the conversion of dry matter to grain yield inany of the trials.

Results of the combined analysis of variance indicated asignificant site-year x crop species interaction for grain yield(Table 2). This interaction was caused by differences in yieldtrends between sites for canola compared with those of wheatand field pea. For example, at the driest site (Carman in1989), all crops yielded between 1807 and 2056 kg ha-t.Under higher precipitation conditions at Portage in 1989 andat both sites in 1990, wheat and freld pea yielded between3046 and 422lkg ha-r, while the yield of canola stillremained near 2000 kg ha-'. Therefore, while wheat andfield pea responded positively to higher levels ofprecipita-tion at Portage in 1989 and 1990 and at Carman in 1990,canola yield appeared to be affected by other factors. Anexplanation for this differential response among crops is thatair temperature (Table 1), which varied less between site-years than precipitation, may have had a greater effect oncanola yield than precipitation. Air temperatures above 25oCat or shortly after flowering are damaging to flowering andpod set in Westar canola (Morrison et al. 1989). These resultspoint out that aerial conditions (i.e. air temperature) can bemore important than a change in tillage system in determiningcrop yield.

40

208nCizo €

CLrnn (l,

(J(D80E

60=.9

40J205arIi"zo =-'6too -80

60

20

o177 r93 206 220 232 242

DOY

Fig. 4. Seasonal dry matter accumulation, canopy light intercep-tion, and crop height for crops under ZT andcT at Fortage in 1990.* and *'* indicate significance of T and T x S interaction at the 0.05and 0.01 probability levels, respectively. DOy indicates day of year.

light interception (Figs. 1-4), however, indicates that wheretillage did affect canopy development, all three test cropsresponded similarly.

While the crop phenology data collected in this study couldnot be analyzed statistically, results indicated no markeddifferences in crop development between tillage systems.These results support similar observations for spring wheat(Gauer et al. 1982; Carter and Rennie 1985: Lafond et al.1992) ard fieldpea (Iafond et at. lgg2),while Wright (19g9)observed delayed development of canola when preplanttillage was eliminated.

Ylrld Compon.nts rnd Grain yieldFew significant tillage responses for yield components wereobserved in this study (data not shown). A T x S interactionfor pods or spikes m-z occurred at Carman in 1989. Thebasis of this interaction was a higher-pod number per unitarea for canola under ZT (5858 m-z) compared with CT(ffi| m-2), while the other two crops *e.e unaffected bytillage system. No significant effects were observed for seednumber per pod or per spike at any of the sites, indicatingthat conditions for seed set were similar for all three cropsurldler ZT and CT. A significant T X S interaction for seed

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BORSTLAP AND ENTZ _ CROP BESPONSE TO ZERO.TILLACE 417

Crop QualityHectolitre weight, grain protein concentration, and grainprotein yield were not significantly affected by tillage system

in any of the trials in this study (data not shown). This con-firms earlier results for wheat and canola reported by

Donaghy (19'73). The similarity (P > 0.05) of grain pro-tein concentration and grain protein yield for ZT and CT indi-cates that the broadcast method of fertilizer N applicationdid not disadvantage ZT crops in this study.

Oil concentration of canola was significantly affected bytillage in one of four trials (data not shown). Although thisdifference was statistically significant, biologically, a differ-ence of 0.2 percentage units is of little importance. particu-larly considering that oil yield was unaffected. Previousstudies showed that ZT did not signifrcantly affect oil con-centration in sunflower (Deibert 1989). In the present study,chlorophyll concentration of canola was also unaffected bytillage system, suggesting that maturation rate was similarfor canola under ZT and CT.

Crop Water UseSeasonal cumulative ET for the four sites is shown in Fig. 5.

At Portage in 1989, significant T x S interactions for ETin four of the five sampling periods indicated a strongdifferential response of canola, wheat and field pea to ZT.

Cormon (1989)ZERO TILL: conolo >--<

peo 'l.---awheol F --{CONV TILL:conolo +<

peo a-wheot 04

In each case the trend was the same; canola and f,reld pea

had a higher ET under ZT while ET of wheat was lowerunder ZT than CT. Higher seasonal water extractionby ZTcanola resulted in a significantly higher total ET at harvest

for canola at both Portage and Carman in 1989.

Signihcant tillage effects at Carman in 1990 indicated that

ET *as lower under ZT compared with CT on five of the

six sampling dates (Fig. 5). This observation was attributed,in part, to less water extraction between 90 and 130 cm forall three ZT crops. For example, water extraction in the 90-

to 130-cm soil depth increment between seeding and harvest

was -1.9 mm for ZT compared with 16.7 mm for CT(difference significant at P I 0.05). These results indicate

that root activity of all three crops was shallower in the ZTcompared with the CT treatments.

A differential response of crop species to tillage system

was observed for pattern of soil water extraction in 1989 at

Portage (Table 3). While ZT increased soil water extraction

between 30 and 90 cm for canola and field pea, water extrac-

tion by wheat (especially between 50 and 90 cm) was lowerunderZT than CT. In previous studies (Chevalier and Ciha

1986; Varvel et al. 1989), reduced ET for ZT wheat was

attributed to poor early growth and a smaller root system

under ZT compared with CT. Cooke (1992) found that when

wheat followed wheat in a crop rotation, the root system was

300

250

200

rRrl

too

o

E znaE

; z5o9k 2ooEo- t50azEt-b50(L

SoUJ

?5zIFEdazEFo(L

sUJt34

150

roo

5n

?Ez,oFEo-azEFo(L

sUJ

E

z9t-

E_

azEF(L

sUJ

Cormon (1990)

r85 r98

DOY

214 233

t52 177 193 206 220 241

DOY

r5l r65

Portoge (1989)

t80 r87 t94

DOY

207 220

300

250

200

r50

roo

300

250

200

f!*rS*

170 raA rq2 lqq 214

DOY

Fig. 5. Seasonal cumulative evapotranspiration of canola, field pea and wheat under ZT and CT. 'r and t'{< indicate significance of T and

T x S interaction at the 0.05 and 0.01 probability levels, respectively. DOY indicates day of year.

Portoge il990)

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418 CANADIAN JOURNAL OF PLANT SCIENCE

smaller due to root diseases. A signif,rcant T x S interactionfor postanthesis water extraction at the Fortage (1989) site,however, indicated that wheat extracted more water between10 and 30 cm under ZT compared with CT, while the othertwo crops were unaffected (data not shown). This observationsupports Baeumer and Bakermans (1973) who found that rootgrowth of wheat under ZT was more intense at shallow depths.

The reasons for enhanced soil water extraction by canolaand field pea under ZT at the Portage (1989) site (Table 3)are not clear. However, the fact that water extractionresponses to tillage were different for canola and field peacompared with wheat points out that a change in tillagesystem can affect crop root activity, and not all crops willrespond alike.

It is important to note that total profile soil water contentat spring seeding was similar (P > 0.05) between tillagesystems in all four trials. Therefore, any differences in ETamong tillage systems in this study were due to in-seasoneffects, not to greater soil water conservation undet ZT.

Evapotranspiration Eff iciencyEvapotranspiration eff,rciency (ETE) was calculated forpreanthesis and postanthesis DM accumulation, total DM at

Table 3. Soil water extraction between seeding and harvest for canola,figld peq and wheat grown under zero-tillage (ZT) and conventional-tillage (CT) at Portage in 1989. Only soil depths where siErificant tillage

x crop species interactions occurred are shown

Canola Field Pea Wheat

CT ZT CT

crop maturity, and grain yield (Table 4). Significant differ-ences in ETE between tillage systems were observed in only3 of 16 instances. Where differences were observed (Portagein 1989 and Carman in 1990), the trend was for a higherETE under ZT. Although no tillage effects were observedfor ETE of preanthesis, postanthesis or growing season DMaccumulation at Portage in 1990, ETE of DM accumulationduring the first 30 d of crop growth was higher (P < 0.05)under ZT than CT (3.8 kg ha-' mm-' vs. 3.1kg ha-'mm-l;. Others also have noted higher ETE for early seasongrowth under ZT (Unger 1990). Signifrcant T x S inter-actions for ETE were observed for postanthesis DM accumu-lation at Portage in 1989 and Carman in 1990. In eachinstance, field pea was found to respond more favourablyto ZT than canola or wheat (Table 4). A similar interaction(P : 0.0686) was observed at Carman in 1989. In termsof ETE, wheat appeared to be least favoured by the shift fromCT to ZT.

Many previous workers have attributed higher ETE underZT to lower evaporative soil water losses (Unger 1990). Thisexplanation appears to apply in the present study as well.For example, although crops at Carman in 1990 used sig-nificantly less water under ZT (Fig. 5), DM accumulationand grain yield were not different, resulting in a higher ETEfor ZT crops (Table 4). Since yield:transpiration ratios arerelatively constant within a crop species (Fischer and Turner1978), it follows that the additional water used in the CTsystem was likely lost by evaporation from the soil.

SUMMARY AND CONCLUSIONSThis study assessed some agronomic and physiologicalresponses of Wesar canola, Victoria field pea and l(atepwawheat to ZT. ZT significantly affected crop growth and canopydwelopment in only a few inshnces. Where tillage effects wereobserved, plant performance was usually enhanced urfier ZT.Where T x S interactions were observed, field pea responded

Soil depthIncrement (cm) CTZT

30-5050-7070-9030-90

(mm water extracted)

r5.4 7.8 3.6 6.8 4.1 4.37.4 2.0 7.6 1.0 1.2 7.63.1 l 8 4.6 3.2 0.6 5.6

2s.9 11.6 15.8 11.0 7.9 17.5

TXS*TXS*TxS*TXS*

*,**Significant at the 0.05 and 0.01 probability levels.

Table 4. Evapotranspiration use efliciency ftg h" - t mm - I ET) for prcanthesis, postanthesis and total growing season dry matter production (DIvf)and grain yield of canola, field pea and wheat grown under zero iillage (ZT) ind conventional tillage (CIi at two locations i; l9E9 and 1990

Canola Field pea Wheat

Location CTZTCTZT

Carman r989

Portage

1990

1989

1990

Preanthesis DMPostanthesis DMGrowing season DMGrain YieldPreanthesis DMPostanthesis DMGrowing Season DMGrain YieldPreanthesis DMPostanthesis DMGrowing season DMGrain YieldPreanthesis DMPostanthesis DMGrowing Season DMGrain Yield

12.933.824.7r 1.42r.63s.628.89.9

24.r51.925.3

8.015.955.028.27.8

10.143.228.2tt.715.530.722.s9.0

24.962.327.29.2

t4.652.026.4

8.4

10. I51.228.0t4.321.775.745.418.812.9

t07.435.715.311.058.727.712.5

9.54r.224.213.321.551 .335.515.614.060.939.217.210.667.630.811.8

8.939.81A 1

12.437.246.941.716.821.9

t15.242.4t4.719.4

103.046.6t4.5

8.558.732.613.230.948. I39.415.717.7

l3 1.038.913.4r8.784.939.814.1

NSNSNSNSNSTxS*zNSNSNSTxS*xT*vNSNSNSNSNS

zT x S, tillage x crop species interactions.YT, tillage system effect.*,**Significant at the 0.05 and 0.01 probability levels, respectively; NS, not signif,icnt

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BORSTLAP AND ENTZ - CROP BESPO'VSE TO ZERO'TILLAGE 419

more positively to ZT than the other two crops. This supports

a similar observation by Lafond et al. (1992) and suggests

that field pea is not only well adapted to ZT production, butthatZT may actually improve field pea productivity. Of the

three crops included in this study, wheat appeared to be least

favoured by the shift from CT to ZT. This may be attributedto the type ofcrop rotation used (i.e. cereal following cereal)(Cooke 1992).

Higher ETE under ZT compared with CT in the present

study was attributed to less soil water evaporation. Thissupports similar previous conclusions (Unger 1990). Whenput into the framework for efficient crop water use proposed

by Pierce and Rice (1988), it was clear that higher ETE underZT inthepresent study was due to greater physiological effi-ciency, not to greater recovery efficiency. In fact, recoveryefficiency (i.e. soil water extraction) was sometimes reduced

under ZT. Evidence from the Portage (1989) site, wherewater recovery effrciency under ZT was decreased for wheat

and increased for canola and freld pea, underscores the

importance of further research to assess the impact of ZTon crop root activity.

Grain yield was unaffected (P > 0.05) by tillage system,

and the lack of signifrcant T x S interactions for grain yieldindicated that the three test crops respond the same to ZT.While differences between tillage systems may have been

greater had growing conditions been drier (especially at the

three sites where differences in crop residue between tillagetreatments were large), it is important to note that growingconditions at these three sites were close to the long-termaverage for southern Manitoba. It can be concluded, there-fore, that under typical southern Manitoba growing condi-tions (and under wetter than average conditions, i'e. Portagein 1990), the agronomic performance of Westar canola,Victoria field pea and Katepwa wheat grown on cereal stubble

should not be expected to differ much between CT and ZT.This is assuming, of course, that leaf diseases are controlled.Therefore, it appears that when growing wheat, canola orfreld pea on cereal stubble in this region, producers shouldbe able to capture the benefits of ZT (e.g. reduced energyconsumption in crop production, less soil erosion) withoutsacrificing grain yield.

ACKNOWLEDGMENTSThe authors gratefully acknowledge the technical assistance

of Mr. Keith Bamford and Mr. Alvin Iverson. This researchwas supported by the Natural Sciences and EngineeringResearch Council of Canada, The University of Manitoba,and Manitoba Agriculture.

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