CENTRE FOR AGRICULTURAL RESEARCH IN SURINAM
CELOS, P.O. Box 1914, Paramaribo, Surinam
C O N T E N T S
Scientific staff 4
9. Hand tools in agriculture 23
10. Hydrology 25
12. Plant breeding 30
14. Silviculture 35
16. Soil fertility and plant nutrition 37
17. Tillage 39
Visiting staff members
DR. 1R. J .H.A. BOERBOOM, Silviculturist** (Dept. of Forest
Management, Forest Mensuration, and Silviculture and Forest
Protection in the Tropics, Agric. Univ. Wageningen)
IR. N.R. DE GRAAF, Silviculturist* (Dept. of Forest Management,
Forest Men suration, and Silviculture and Forest Protection in the
Tropics, Agric. Univ. Wageningen)
IR. H.J. HOEFMAN, Agricultural Economist** (Dept. of Agricultural
Economics of the Tropics and Subtropics, Agric. Univ.
Wageningen)
IR. C B . HOUTMAN, Agricultural Economist* (Dept. of Agricultural
Economics of the Tropics and Subtropics, Agric. Univ.
Wageningen)
IR. P.J. HUMMELEN, Entomologist (Dept. of Entomology, Agric. Univ.
Wage ningen)
DR. IR. B. H. JANSSEN, Soil Scientist* (Dept. of Soils and
Fertilizers, Agric: Univ. Wageningen)
IR. R.W.R. KOOPMANS P H . D . , Hydrologist (Dept. of Land Drainage
and Land Improvement, Agric. Univ. Wageningen)
IR. J.K. KOUWENHOVEN, Agricultural Engineer** (Dept. of
Agricultural Engineer ing, Agric. Univ. Wageningen)
DR. IR. G. A.M: VAN MARREWIJK, Plant Breeder (Dept. of Plant
Breeding, Agric. Univ. Wageningen)
IR. T. VAN DER SAR, Agricultural Engineer* (Dept. of Agricultural
Engineering, Agric. Univ. Wageningen)
DR. G. STARITSKY, Botanist** (Dept. of Tropical Crops, Agric. Univ.
Wageningen) IR. F.J. STAUDT, Forest Engineer (Dept. of Forest
Utilization, Forest Policy and
Tropical Forest History, Agric. Univ. Wageningen) DR. IR. J.F.
WIENK, Agronomist (Dept. of Tropical Crops, Agric. Univ.
Wage
ningen)
1. DIRECTOR'S REPORT
1.1. GENERAL
Due to a revaluation of opinions and the rapidly increasing number
of students en rolled in the State Agricultural University
(Wageningen, the Netherlands) less scientific staff than expected
could be seconded to CELOS. As a result, during the year under
review the further expansion of the Centre proceeded not as fast as
had been planned.
In 1971 the aggregate number of months the various scientists
worked at CELOS increased from 128 in 1970 to 139. The
corresponding student figure was 101, versus 99 in 1970.
Work in several new disciplines was started. In some others it was
closed or had to be interrupted because of the departure of the
scientists concerned without their being replaced in time.
As a part of its efforts to put into use Surinam's almost
uninhabited interior the Government instituted an organization
responsible for the establishment and main tenance of experimental
gardens in that region. The Centre was invited to participate in
the reconnoitring research to be carried out at those stations.
Preparations were made to tackle this new line of work in
1972.
1.2. SCIENTIFIC STAFF
Dr. G. Staritsky, botanist, returned to the Netherlands on 12 May,
and has not yet been replaced.
Ir. H.J. Hoefman, agricultural economist, completed the field work
of his study on the contribution of agriculture in the Nickerie
distria (West Surinam) to the national and regional economy, and
left Surinam on 26 May to resume his duties in Wageningen. His
successor, Ir. C.B. Houtman, arrived on 19 February:
Dr. Ir. J.H.A. Boerboom, silviculturist, who started the Centre's
research on forest ecology and silviculture, returned to the
Netherlands on 30 June. He deputed his task to Ir. N.R. de Graaf
who arrived in Surinam on 19 January.
Ir. J. K. Kouwenhoven, agricultural engineer, left the country for
Wageningen on 8 October, after transferring his duties to Ir. T.
van der Sar, in Surinam since 9 Fe bruary.
Dr. Ir. B.H. Janssen joined CELOS as a soil scientist on 26 March.
Ir. E. Bessems, who in the years 1969/70 at CELOS investigated
nitrogen fixation
in the phyllosphere of grasses spent the months June and July at
the Centre for some additional research.
1.3. STUDENTS
Twenty-three students of the Agricultural University were attached
to the Centre a? against 22 in 1970. After conclusion of their
period of practical work six of them
carried out research projects for their main subject, viz. crop
production, plant breed ing, hydrology, water purification or
nature conservation. For many other students, like in previous
years, posts were found in government services and private
enterprises.
1.4. LAND AND BUILDINGS
During the year the second unit of the main building was completed
by adding to the part constructed in 1967/68 two office and
laboratory wings and a central section housing common
facilities.
One of the greenhouses built in 1969 had a roof of polyester panes.
Unfortunately the material turned out to be defective, resulting in
a rapid decline of light trans mission. For that reason the
polyester was replaced by hammered glass.
1.5. REVIEW OF RESEARCH
In the field of crop botany experiments were carried out to study
the effect of spacing on production and distribution of dry matter
in food crops, this time grain sorghum and cowpea. In the former
also the effect of spacing on inflorescence ini tiation and
differentiation as well as panicle size was investigated. A growth
analytical comparison of IR 8 and the new Surinam rice variety
Acorni showed a more rapid development of IR 8 during the early
stages, but eventually Acorni reached a higher total dry weight and
a higher grain yield.
Crop production research was limited to several comparative yield
trials with sweet potato, cowpea and groundnut.
Entomological research remained focussed on the two major rice
borers, Diatraea saccharalis and Rupela albinella. Life history
studies of both species were continued with the main purpose of
achieving a better insight in the plagues' development throughout
the year. Emphasis was also on the collection, identification and
study of their indigenous parasites and predators.
In Surinam, like in many other developing countries, the production
and marketing structure of vegetables and fruit is a rather
confusing affair. In an attempt to make the production side more
transparent a farm management study was started cover ing 150
farms of various sizes and involving frequent on the spot
collection of all relevant input and output data.
In addition to the succession studies in the lowland rain forest
already in progress, forming the body of forest ecology research,
an investigation into the natural propaga tion of Cecropia spp.
was undertaken. Evidence was obtained that seeds of these species,
being very typical for the secondary vegetation following clearing
of the original high forest, may survive for a prolonged period in
the forest soil.
In forest exploitation research emphasis was on work physiological
studies. Various types of measuring equipment were tested to find
suitable methods of determining the physical effort involved in
tree felling with axes and hand and power saws.
Research in the field of genetics and cytogenetics was again
focussed on the sex mechanism in pawpaw and the genetical basis of
some seed coat characteristics in cowpea. Definite conclusions
cannot yet be drawn.
It is no exception that in Surinam hand tools, though being
indispensable on any farm irrespective of its degree of
mechanization, do not receive the attention they deserve. To make
up for this a comparative study was started to determine for
various types and models of tools the durability, the quality and
quantity of the work done
and the physical effort involved in using them. First tested were
mowing and weed ing tools.
Hydrology research was more diverse than in preceding years.
Rainfall measure ments at different levels over the ground failed
to demonstrate differences under the local climatic conditions. The
time consuming installation of a weighable lysimeter was nearing
completion. An experiment concerned with the possibilities of
subsurface drainage in a heavy clay soil produced the first
results. Last but not least a water budget study of the
CELOS-polder was undertaken.
In support of the above mentioned management study on farms
producing veget ables and fruit, investigations were started into
their marketing and consumption. The former include direct
observations on the central market of Paramaribo and talks with
traders, the latter a study of consumer behaviour in relation to
supply and prices.
In plant breeding research the studies of fruit setting in sweet
potato as affected by incompatibility and sterility and of
cytoplasmic male sterility restoration in sorghum were continued.
Breeding work to arrive at synthetic varieties of maize made good
progress.
Like in the year before progress of the multidisciplinary research
project on content and quality of protein in major tropical food
crops was hampered by difficulties met in having the numerous
samples analysed. To make up leeway in the laboratory the field
work was slowed down.
Studies on the natural regeneration of worked-out areas of the
lowland high forest under different tending regimes were continued.
Though a remarkable decrease in average girth increment was noted,
presumably as a result of severe drought in the second half of
1969, this did not eclipse the marked reaction of the vegetation to
differences in tending regime. Other silvicultural work included
new studies of the root system of Caribbean pine.
Soil science and plant nutrition research is a new topic in the
Centre's programme. Several experiments concerned with laboratory
procedures were carried out. In addi tion work was started to test
the suitability of a new pot experiment technique as a method for
quick identification of the nutrient status of soils in areas not
yet well known.
In the year under review upland rice and Croialaria sp. (long wet
season) followed by maize and soyabeans (long dry season) were
grown in the long-term field trial started in 1970 to study the
effect of tillage and non-tillage on a heavy clay soil under
permanent cropping. In addition to this experiment a similar trial
was begun on a light sandy soil in the savannah zone of
Surinam.
Wood technology research remained focussed on specific gravity and
moisture con tent in different sections of the stems of standing
Caribbean pine.
16. CONTACTS
The large number of authorities and scientists visiting the Centre
included Dr. J. Sedney and Dr. Ir. F. Essed, the Surinam
prime-minister and minister of natural resources respectively, Dr.
A. H. Boerma, director-general of the FAO, Dr. T. S. B. Aribisala,
director of the agricultural services division of the same
organization, Ir. P. van der Schans, director of agricultural
education in the Netherlands, Ir. G. P. Tiggelman, president of the
International Agricultural Centre at Wageningen (the Netherlands),
and Ing. R. Canet Pellicier, director of the Rice Research Station
of the University of Havana (Cuba).
Dr. Boerboom was again a visiting lecturer to the Forestry Faculty
of the Andes University (Mérida, Venezuela), this year from 26
January to 3 March. Dr. Wienk attended the 'conference on the
intensive management and use of forage crops in the tropics and
their utilization by ruminants' held in Guadeloupe during the last
week of May.
CELOS was host to the scientific sessions of the 'meeting of
experts on the mechanization of rice production and processing', an
international conference held from 27 September to 2 October and
organized by Surinam, the Netherlands and FAO.
1.7. PUBLICATIONS AND REPORTS
The following CELOS Bulletins were published : 13. Report for the
year 1970 of the Centre for Agricultural Research in Surinam
(English; Portuguese and Spanish summaries). 14. VAN MARREWIJK,
G.A. M. Algemene aspecten van de veredeling van eenjarige
tropische gewassen (Dutch ; English summary). 15. RUINARD, J.
Nature and assessment of losses caused by sugarcane borers (English
;
French summary). Like in previous years mimeographed "CELOS
Quarterly Reports" and "CELOS
Reports", both in Dutch, were issued. The latter comprised the
numbers 44 to 60 and dealt with root rot of Caribbean pine, various
siivicultural and forest ecological topics, investigations in the
field of forest exploitation and wood technology, miscellaneous
studies on the rice borers Diatraea sacchardtt and Rufiela dbmella,
growth analytical work in sorghum and cowpea, a comparison of
several tillage and zero-tillage systems, soil drainage by means of
plastic tubing and other hydrological studies, sterility and
incompatibility research in sweet potato, inheritance of some seed
coat characteristics in cowpea, and the contribution of agriculture
ia the Nickerie district to the regional and national
economy.
1.8. ACKNOWLEDGEMENTS
We are gready indebted to Dr. José H. da Costa Ferreira for
translating the sum mary of this annual report into
Portuguese.
2. CROP BOTANY
2.1. PRODUCTION AND DISTRIBUTION OF DRY MATTER IN Sorghum bicolor
(L) MOENCH cv. MARTIN AS AFFECTED BY SPACING (70/17)
The effect of spacing on the production and distribution of dry
matter in the semi- dwarf sorghum cultivar Martin was studied by
regular sampling of a field trial in which three spacings were
compared, viz. 20 x 20, 30 x 30 and 40 x 40 cm. The treatments were
arranged in a randomized block experiment with four replicates.
Samples were taken in the period 39-97 days after sowing at roughly
weekly inter vals, and consisted of 4 x 12 plants per spacing. The
final harvest took place 108 days from sowing. The trial was
planted at the onset of the short rains. Weather condi tions
appeared most unfavourable for sorghum. Over 730 mm of rain were
recorded during the growing period of which 320 mm fell during the
first 40 days. As a result crop growth was adversely
affected.
At the time of the first sampling there were no clear differences
in total dry weight per plant between the three spacings. Total dry
weight in the period 39-81 days after sowing increased almost
linearly. Straight lines were fitted to the treatment means using
the method of least squares. Regression coefficients for the 20, 30
and 40 cm spacing were 0.584 ± 0.028, 1.006 dt 0.050 and 1.023 ±
0.061 respectively, cor responding with crop growth rates of 146,
112 and 64 kg/ha per day. During the entire growing period
differences in dry weight per plant between the widest two spacings
were small and not significant.
Maximum LAI values, recorded 53-57 days after sowing, i.e. before
heading, were 3.54, 1.97 and 0.98 for the 20, 30 and 40 cm spacing
respectively. Leaf area per plant rapidly decreased thereafter, the
decrease being virtually linear at all spacings.
Net assimilation rates were calculated by using the regression
equations for total dry weight and leaf area per plant. After
heading the rates increased with decreasing leaf area, the increase
being highest at the closest spacing. The wider the spacing the
higher the net assimilation rate.
Panicle weights at the final harvest were 47.6, 81.9 and 89.3
g/plant for the 20, 30 and 40 cm spacing respectively. The
differences could be entirely attributed to number of grains per
panicle; 1000-grain weight was not affected. Final yields were
2.98, 2.26 and 1.40 ± 0.29 tons/ha on a basis of air-dry
weight.
2.2. INFLORESCENCE INITIATION, INFLORESCENCE DIFFERENTIATION AND
PANICLE SIZE IN Sorghum bicolor (L) MOENCH cv. MARTIN AS AFFECTED
BY SPACING (71/6)
In spacing experiments with sorghum normally the size of the
panicle is negatively correlated with plant density suggesting
inter-plant competition at early growth stages. To investigate the
effect of light on inflorescence initiation and differentiation,
ex cluding possible competition for water and nutrients, a pot
experiment was conducted in which the spacings 15 x 15 cm and 30 x
30 cm were compared in a randomized
block design with four replicates keeping pot size the same for
both treatments. Plots were sampled daily for a period of 10 days
starting 19 days from sowing, the fre quency of sampling being
reduced to once every two days thereafter. Each sample consisted of
a total of 12 plants which were examined microscopically for inflo
rescence initiation and differentiation. Furthermore dry weight and
leaf area were determined.
Parallel to the pot experiment a field trial was run in which the
effect of the two spacings was investigated on the amount of
sterile spikelets and on the size of the panicle. The field
experiment, which comprised eight replicates, was planted towards
the end of January, i.e. during the short rains.
At the first sampling of the pot experiment all plants were still
completely vegeta tive. Differences in dry weight and leaf area
did not occur until 30 days from sowing, when the LAI had reached
values of 1.00 and 0.24 for the 15 and 30 cm spacing respectively;
inflorescence initiation had taken place a few days before. Dry
weight and leaf area curves for both spacings clearly diverted
thereafter, the growth rate of the 30-cm spaced plants being higher
than that of the 15 cm ones.
Data collected on the size of the inflorescence primordia have been
insufficiently processed to be able to decide as to the exact stage
at which the inter-plant compe tition exerted its influence on the
development of the young panicle.
Due to adverse weather conditions plant growth in the field trial
left much to be desired. Nevertheless, at heading the number of
sterile spikelets appeared much higher at the narrow spacing than
at the wide one. There was also a marked difference in total plant
weight. At ripeness relatively more dry matter appeared to have
been stored in the panicle at 30 x 30 cm than at 15 x 15 cm.
Differences in panicle weight were found to be entirely due to
differences in grain number ; the heads of plants at 30 x 30 cm
contained over three times the number of grains of those at 15 x 15
cm; 1000-grain weight had not been affected.
2.3. A GROWTH ANALYTICAL COMPARISON OF THE RICE CULTIVARS IR 8 AND
ACORNI (71/7)
The promising Surinam rice cultivar Acorni was compared with the
cultivar IR 8 in terms of production and distribution of dry
matter. The study comprised a pot experiment to compare the growth
during the first 30 days and a field trial for the remainder of the
growth cycle.
The pot experiment was sampled every three days starting three days
after sowing. Sowing took place with seeds that had been soaked for
48 hours. The first five samples comprised 250 seedlings per
cultivar, this number being reduced to 50 in the period
thereafter.
The field trial was of the randomized block design with six
replicates. Plants were raised in a nursery for a period of 25 days
before being transplanted to the field at a spacing of 20 x 20 cm,
one plant per hill. Sampling was done at weekly intervals starting
11 days after transplanting. The last samples were taken 90 days
after trans planting for Acorni and 97 days for IR 8. The final
harvest took place 9 respectively 14 days later.
During the first two weeks total dry weight in the pot experiment
was greater for Acorni than for IR 8, the difference being due to
the larger grains, which were included in the plant weight. After
three weeks plants of IR 8 were heavier and had more leaves and
stems than those of Acorni. Total dry weight of IR 8 plants
increased
10
more or less linearly with age. The rate of increase in dry weight
of Acorni descreased with age so that at the end of the pot
experiment the plants weighed less than half those of IR 8. Also
its number of leaves and stems was 50 percent less. Plant height
was not affected.
At the first sampling of the field trial plants of IR 8 were
already heavier than those of Acorni. The former also had more
leaves and more stems, a difference that was maintained during the
entire experiment. The difference in plant weight was in faveur of
IR 8 up to 113 days from sowing. Total dry weight of Acorni
increased virtually linearly up to the last sampling. That of IR 8,
however, increased very little after 92 days so that Acorni
eventually reached a higher total dry weight. At the last sampling
Acorni plants weighed 46.6 g as against 37.8 g for IR 8.
Leaf number reached a maximum 78 days after sowing when 77 leaves
per plant were recorded for IR 8 and 49 for Acorni. Leaf number
decreased very rapidly there after, the rate of decrease being
largest for IR 8. Maximum LAI values were 6.5 for IR 8 and 4.5 for
Acorni. At the last sampling the LAI had dropped to 2.8 and 2.6
respectively.
Relative light intensities measured below the crop showed that the
reduction in light intensity below IR 8 was 40-50% more than that
below Acorni.
Heading in Acorni was observed 85 days from sowing, i.e. 5 days
earlier than in IR 8. Panicle weight was first determined 92 days
from sowing. It increased linearly for both cultivars during the
next two weeks. For Acorni the increase in panicle weight then
remained constant up to the last sampling. For IR 8 the rate of
increase clearly decreased so that panicles of IR 8 eventually
weighed least, i.e. 16.6 as against 19.9 g. Though not
statistically different the grain yield at 12% moisture content was
higher for Acorni (4.80 tons/ha) than for IR 8 (4.06
tons/ha).
2 4. PRODUCTION AND DISTRIBUTION OF DRY MATTER IN THE COWPEA (Vigna
unguku- lata (L.) WALP.) CULTIVARS AFRICAN RED AND PI 221731 AS
AFFECTED BY SPACING (71/17)
Two morphologically distinct cowpea cultivars, African Red (AR) and
PI 221731 (PI), were compared in terms of production and
distribution of dry matter at different spacings, by regular
sampling of a 3 x 2 split-plot experiment with four replicates
planted at the end of the long rains. Spacings were 20 x 20, 30 x
30 and 40 x 40 cm. Samples were taken from 27 days after sowing
onwards until pods were dead-ripe, and consisted of 12 plants per
sub-plot. The frequency of sampling was twice a week in the period
27-55 days after sowing, the interval between samplings increasing
to 5 or 7 days thereafter. Entire plants were harvested. Rainfall
registered during the crop's growing period amounted to 275
mm.
In the period 27-55 days after sowing total dry weight of both
cultivars at all spacings increased virtually linearly. Straight
lines fitted to the treatment means yielded regression coefficients
for AR of 0.649 ± 0.046, 1.397 ± 0.063 and 1.967 ± 0.070 at the 20,
30 and 40 cm spacing respectively, corresponding with crop growth
rates of 162, 155 and 123 kg/ha per day. For PI the regression
coefficients were 0.626 ± 0.027, 1.380 ± 0.049 and 1.943 ± 0.058,
and the crop growth rates 156, 153 and 121 kg/ha per day. In the
period 27-55 days from sowing there was no signi ficant difference
in total dry weight between cultivars at comparable spacings.
At the first sampling there were no differences in LAI between
cultivars at com parable spacings. In AR leaf area per plant
increased linearly up to 48 days from
11
sowing when maximum LAI values were reached of 6.24, 5.34, and 4.02
for the 20, 30 and 40 cm spacing respectively. Leaf area in PI
increased much more slowly, the rate of increase decreasing with
age. Maximum LAI values recorded in this cultivar were 3.04, 2.33
and 1.76 respectively, which were reached in the period 45-52 days
from sowing. Once the maximum was reached LAI decreased more
rapidly for AR than for PI, the rate of decrease in the former
being higher with closer spacing.
Nearly all sample plants of AR flowered 45 days from sowing, i.e.
one week later than for PI. Spacing had no effect.
Pod dry weight in the period 48-60 days from sowing increased more
or less lin early, the rate of increase varying little between
cultivars. Pod weight changed little thereafter, the changes being
larger with wider spacing. Pod yields for AR were 2.75, 2.31 and
2.37 tons/ha dry weight for the 20, 30 and 40 cm spacing
respectively. For PI these figures were 2.62, 2.40 and 2.32.
Spacing had no effect on 1000-grain weight.
Net assimilation rates for AR were calculated using the regression
equations for total dry weight and leaf area per plant. Because of
the non-linearity of leaf area curves this was not possible for PI.
However the much lower LAI values for this cultivar suggest a
higher NAR. In AR the NAR decreased with age, the decrease be
coming less as the crop became older. The wider the spacing the
higher the net assi milation rate.
12
3. CROP PRODUCTION
3.1. COMPARATIVE YIELD TRIALS WITH SWEET POTATO, Ipomoea batatas L
(LAM.)
(70/26; 71/3)
To obtain an idea of the yielding capacity of sweet potato under
the conditions of the Surinam coastal area, 12 clones were compared
in a randomized block design with three replications. Half of the
plots were harvested 4Vi months after planting, the ether half one
month afterwards. Each plot consisted of 54 plants spaced 30 x 100
cm, of which 26 served as guard plants. The results are presented
in Table 1.
Table 1 - Average tuber yields (fresh weight ; ton/ha) of 12 sweet
potato clones, har vested 4Vi or 5 Vi months after planting.
Clones arranged in order of yield at the first harvesting date. The
number at second harvest in brackets
months months
AVi
">Vi
(3) (2) (6) (1) (8) (5)
Jersey Orange Genjem 1 Butikatoka Blauwkop Willemsrank Egeida
m ±1.08 4.98 4.13 1.21 0.50 0.18 0.10
5VS
(7) (4)
(12) (9)
CV 41.9 77.5
Four clones amongst which the two local ones Blauwkop and
Willemsrank produced very little at both harvesting dates. Of the
best four producers at the first harvest three again ranked high
one month later. With the exception of Genjem 1 and 2 all clones
were most productive at the first harvest. This may have been
caused by the very wet conditions between first and second harvest,
bringing about decay of the tubers.
The five clones that appeared best in the above experiment at 4Vi
months after planting were compared in a further trial planted
during the short rains of 1971. To reduce intra-block variation the
clones were arranged in a balanced incomplete block design with six
replicates. The trial was planted on cambered beds of about 5 m
wide. Harvesting took place 5 Vi months from planting, i.e. towards
the end of the long rains.
As may be seen from Table 2 yields were extremely low. Most of the
larger tubers had rotten away and some plants had no tubers at all.
Judging from the yield differences
13
between record and guard plaints, the latter of which were mostly
growing along the edges of the beds, excessive water in combination
with the heavy soil may be res ponsible for the poor performance
of the crop.
Tabel 2 - Adjusted mean yields (kg/ha fresh weight) of five sweet
potato clones 5Vi months from planting
clone
record plants
± 54 1752 1536 1524 1103 800
3.2. COMPARATIVE YIELD TRIALS WITH COWPEA, Vigna ungukulata (L)
WALP. (71/5 ; 71/16)
A number of morphologically distinct cowpea cultivars differing in
characteristics such as type of branching, plant height and leaf
size!, were compared in terms of yields. It was hoped that some of
these attributes could be correlated with yielding ability and that
types might be selected for further crop botanical research.
The first trial (71/5) was planted at the end of the short rains on
a sandy soil. Six cultivars were compared in a randomized block
experiment with six replicates. They comprised Capucijner 6101 of
local origin, I.N. 593, Kwarra and Yebba from Nigeria, Blackeye
8152 from the U.S.A. and the South African PI 221731. Because of
unfavourable weather conditions soon after planting, emergence in
three replicates was extremely poor. They were subsequently written
off. The trial was harvested within 70 days from sowing.
In the second trial (71/16) the three Nigerian cultivars were
compared with African Red and Blackeye, both of local origin. The
trial was of the balanced incomplete block design type, and was
planted at the end of the long rains on a heavy loam soil ; there
were six replicates. The trial was harvested within 66 days from
sowing.
The yields obtained in the two trials are presented in Table 3.
Generally yields were not high, as was expected from the moderate
vegetative growth. In the first trial yield differences between
cultivars were small, with the exception of PI 221731. This cul-
tivar is characterized by terminal inflorescences and hence a
limited vegetative growth. A slow early development in this
cultivar results in a small plant with small yields, as was the
case in the present trial (cf. section 2.4). In the second trial
yields of the Nigerian cultivars were more or less the same as in
the first. African Red produced little, the crop's stand leaving
much to be desired. Again vegetative growth Was not abundant in
this trial which was planted only a few days before 71/17 in which
a much better vegetative development and far higher yields were
obtained (cf. section 2.4).
The differences in morphological characteristics were not clearly
correlated with yield differences.
14
Table 3 - Pod yields (tons/ha; 12% moisture content) of a number of
cowpea cultivars as obtained in two different trials
cultivar
Yebba Kwarra I.N. 593 Blackeye 8152 Capucijner 6106 PI 221731
African Red Blackeye
trial 71/5
trial 71/16
1.05 1.27
3.3. A COMPARATIVE YIELD TRIAL WITH GROUNDNUT, Arachis bypogaea L,
(71/15)
A comparative groundnut yield trial was conducted during the long
dry season. The cultivars were Argentine, Natal Common and Spanish
205 introduced from Nigeria, and Matjan and 68056 of local origin.
With the exception of the latter, a Valencia type, all cultivars
belong to the Spanish group; they mature in about 100 days. The
trial was of the balanced incomplete block design type with six
replicates. The yields and some yield components are presented in
Table 4.
Matjan clearly outyie'ded all other cultivars, both in terms of pod
and seed yield. 68056 was the lowest producer, though the
differences with the other three cultivars were not statistically
significant. The three Nigerian cultivars differed little in yield,
1000-grain weight and number of seeds per ha. Both Matjan and 68056
produced considerably less seeds per ha than the Nigerian cultivars
but in Matjan this was more than offset by the size of the seeds.
This was not the case for 68056.
Table 4 - Pod and seed yields (tons/ha; 12% moisture content),
1000-grain weight (g) and estimated numbers of seeds per ha for
five groundnut cultivars
Argentine
655
661
629
491
488
15
4.1. THE RELATIONSHIP BETWEEN RICE BORERS AND THEIR PARASITES
(68/1)
The sampling of lowland rice plots at ŒLOS as mentioned in the
previous annual report, was continued in the same way.
The percentage of infestation by Diatraea saccbaralis was nearly
always below 1, with 5-35% of the borers being parasitized. For
Rupela albinella these percentages were 2-7 and 20-40 respectively.
The percentage of infestation by D. saccbaralis was lower, but that
by R. albinella higher than the year before. As in 1970 a very
clear peak in infestation was observed after the area's rice crop
had been harvested. It occurred one month later than last year, the
harvesting of the rice also being later.
Infestation by D. saccbaralis nearly always takes place when the
rice plants are two months old; R. albinella starts one month
later. One day old first-stage larvae of R. albinella are already
found in the internodes, suggesting that this species requires a
stem cavity for its development.
After the rice on the small-holders' plots in the neighbourhood of
CELOS has been harvested, the borers appear to concentrate on the
CELOS-fields there being no other rice left in the area. From that
moment onwards the plants were very carefully examined to find also
the small borer larvae. About 20% of D. saccbaralis larvae found
were dead; for R. albinella this figure was about 15. Most of the
pupae of D. saccbaralis were dead or nearly so when found, whereas
for R. albinella this was about 25%.
Tricbogramma sp. and Telonomus sp. were reared from eggs of D.
saccbaralis. Other parasites found were the same as those mentioned
in the reports of previous years.
In 1971 weekly samples were taken in four lowland rice plots of
small-holders. One plot showed some, the others virtually no
infestation. However, this year rice planting took place very
late.
4.2. THE BIOLOGY OF THE BORERS' PARASITES (70/32)
Agathis stigmaterus, the most important parasite of Diatraea
saccbaralis in rice, is now being reared continuously in two ways :
(i) First-stage larvae of Diatraea saccbaralis are placed on young
potted rice plants
kept in cages. After 6-10 days, when larvae have reached stage
L2-L4, a wasp is released into the cage. After a further few days
the larvae are recovered and placed onto an artificial medium to
await the wasps' development.
(ii) The wasp is reared entirely on an artificial medium. The
larvae to be parasitized are 6-10 days old and are kept in
Erlenmeyer flasks. The wasps are placed in the flasks where they
parasitize the larvae through cavities the latter have eaten in the
medium.
It takes 30-40 days for the wasps to develop. The maximum number of
parasite larvae hitherto found in one borer is three.
16
<;
Dr. J. H. E. ferrier. Governor of Surinam, opens the 'meeting of
experts on the mechanization of rice production and
processing'.
Letting down the lysimeter tank into the cellar.
4 3. PREDATORS OF RICE BORERS (71/12)
Ants are important predators of rice borers. Although a number of
species occur in lowland rice, Varatrechina {Nylanderiu) sp. is by
far the most important one. It rarely if ever feeds on eggs of
Duttraea saccbaralis but particularly eats the just emerged larvae.
These ants make nests of clay and organic material between the
stems of a rice plant just above the water level. There are small
and large nests. The smaller ones, which are usually located
between leaf sheath and stem, are made without clay. The larger
ones may enclose the lower 10 cm of all stems of a plant hilL The
contents of an ant nest may vary widely. If there are many winged
ants there are virtually no eggs. The largest number of individuals
found in one plant hill consisted of 2079 eggs, 1733 larvae, 834
pupae, 72 winged adults, 787 wingless adults and 7 queens. The
average number of adults was 250 per hill. As a rule more than one
queen is found per hill; it is not clear whether one has to do with
one or more nests.
The maximum number of plant hills containing a nest that was found
in lowland rice on the CELOS-fields amounted to 40%. The first
nests are built near the dikes, 3-4 weeks after
transplanting.
On small-holders' plots a maximum of 12% of the plant hills carried
a nest whereas ants were found in up to 50% of the plants. After
harvesting nests may be found for a long time in the straw
remains.
It is striking that at the end of 1971 no ants were seen in the
lowland rice at CELOS, whereas at the end of 1970 they occurred in
large numbers.
4.4. THE BIOLOGY OF Rupela albinella (CR.) (70/20)
As rearing of R. albinella is extremely difficult, the number of
larval stages was determined by measuring the width of the head
capsule of larvae found in the field. Skins with head capsules are
seldom encountered because they are eaten immediately upon
moulting. An exception to this is the second-stage larva, which
does not eat the skin and head capsule of the first-stage one. The
first three larval stages can be easily identified. The Li has a
head capsule that is 0.19-0.20 mm wide, L2 one of 0.30-0.45 mm and
L3 one of 0.45-0.80 mm. As for the stages L4 and L5, these
measurements overlap each other so that the width of the head
capsule may be anywhere between 0.81 and 1.40 mm. Pupation was
found not to take place until the head capsules were at least 0.95
mm wide. These larvae were probably all males.
The mean pupal weight of the female is 140 ± 5 mg, that of the male
63 ± 5 mg. The larva lives in the stem cavity and normally remains
during its entire life in
one and the same internode. On!y when it entered the shorter
internodes at the base of the stem, it may eat its way into one or
two more internodes. Although various larvae may be present in one
stem, never two larvae were found together in the same internode.
An exception may be encountered among the first-stage larvae, but
then only one is alive.
17
5. FARM ECONOMICS
5.1. A FARM MANAGEMENT STUDY OF FRUIT AND VEGETABLE FARMS ( 7 1 / 1
3 )
Dependent on ethnical origin, the Surinamese spends 10-20% of the
money that goes in food on fruit and vegetables. As compared with
other food since 1953 the prices of these commodities have risen by
300-400%.
In order to obtain information on the underlying causes of these
price increases a study was started on the production of fruit and
vegetables, their marketing and the behaviour of the consumer in
relation to these products' prices. This study comprises: (i) a
farm management study of the faims producing fruit and vegetables ;
(ii) a study of the marketing of vegetables (see section 11); and
(iii) a study of the consumers' behaviour (see section 11).
The farm management study was started to gain an insight into : (i)
the supply of fruit and vegetables ; among others in relation to
season and type
of products; (ii) the important inputs such as land, labour,
capital and know-hew ; and (iii) the farmers' reaction to prices,
innovations, etc.
A total of 150 farms were selected in a stratified sample, the
criterion being the total area under vegetables. A requirement was
that most of the produce had to be sold. For the selection the data
of the Agricultural Census 1969 were used.
In May of this year the field work was started with an inventory of
the selected farms. From the beginning of July onwards data have
been collected on labour, cost and yields. To this end the farms
were visited three times a week. The work is to be continued until
August 1972.
After having been checked and if necessary amended, the inventory
forms were coded and sent to Wageningen, The Netherlands, where
they have been processed for the electronic computer.
The "daily" forms are being summarized over two-week periods, and
the totals coded and also sent to Wageningen for further
computing.
In order to obtain some interim information, in February 1972 a
first, simple analysis will be made of the commodities of which
sufficient data are available. Final pro cessing and analysis will
take place at the Department of Development Economics of the
Agricultural University, Wageningen, The Netherlands, upon
termination of the field work.
18
6. FOREST ECOLOGY
The 1971 measurings of the forest succession plots (67/1) do not
indicate an im portant change of vegetation development. The
oldest plot, at Blakawatra, which has been described in previous
annual reports, still shows the marked difference in vegeta tion
between imperfectly drained and well-drained soil, i.e.
savannah-like vegetation versus low secondary bush.
Some additional permanent plots were staked out for studying forest
succession following shifting cultivation (67/3). Another study
within the framework of this project, and already mentioned in
previous annual reports, resulted amongst others in a
classification in five age-classes of the physiognomy of secondary
vegetations, to be used for terrestrial observation as well as for
interpreting aerial photographs.
The vegetation in the permanent plots for studies of the virgin
forest (67/4) was surveyed again. One of the plots (10 x 1 m) used
for sampling undergrowth showed a remarkable increase in the number
of seedlings established, which was most likely a result of an
increase in incident light from openings in the canopy.
Germination tests with seeds of woody species, especially Cecropia
(70/21), showed some interesting results. Bimonthly sampling of
litter and topsoil from undisturbed forest, determining the viable
seeds present by germination tests, showed the presence of large
numbers of Cecropia seeds per m2 all the year round. Evidence was
obtained that the Cecropia trees in secondary vegetations originate
from seeds already present in the soil at the time of clearing the
original forest. The investigations will be con tinued, and will
include in vivo and in vitro tests on seed longevity.
19
7. FOREST EXPLOITATION
During 1971 the research in this discipline concerned (i) work
studies on, felling large-sized trees with power-chain-saws in the
tropical rain forest of Surinam (71/1), (Ü) work physiciological
studies (70/15) and tests (70/29), and (iii) measuring tech niques
(71/11).
To increase efficiency and safety in felling with the
power-chain-saw, the presently used techniques were analysed and a
process and time study were made of the best gangs.
Work physiological research was restricted to the measuring of work
load and the determination of the prescribed breaks during tree
felling with axes, hamd and power saws, so as to obtain values for
a fair day's work. The ergospirometer after Müller-Franz and the
microgasanalyser after Scholander were used for measuring
ventilation and oxygen consumption; cardiotachograms were obtained
with the aid of a telemetric receiver and recorder.
The tests used to determine the work capacity of men were (i) a
modified Harvard- Step-Test, (ii) the Lüngren-Step-Test, and (iii)
the Ästrand-Submaximum-Test. Test per sons were recruited from
amongst forest workers, CELOS gardeners and students.
Successful experiments were carried out with two types of
stethoscopes, a normal one and a electronic one, in order to obtain
heart rates during step tests and specialized foiest work, such as
planting, weeding and thinning with axes. Both stethoscopes
appeared to be useless, however, in combination with vibrating
machines like power- chain-saws.
20
8.1. THE SEX MECHANISM IN Carica papaya L. (69/2)
In order to obtain information on the genetic background of sex in
pawpaw a num ber of crosses between male (M), female (F) and three
different types of hermaphrodite plants (Hi, H2, H3) had been made
in 1969. Thirty-four progenies, comprising the combinations FxM,
FxH3> FxH2, FxH^ HixM, HixH3, Hi selfed, H2XM, H2 selfed, H3xM
and H3 selfed were selected and planted in the field at the end of
the first quarter of 1970. Due to unfavourable weather conditions
early growth was bad so chat in most plants flowering did not start
until the end of that year. For further details the reader is
referred to the annual reports for 1969 and 1970.
From December 1970 until July 1971 weekly observations were made,
one to four flowers of each plant being described at each
observation. Description included (i) position of the flower in the
inflorescence, (ii) tube/lobe ratio of the corolla, (iii) ovary
size, and (iv) number and insertion of stamens. Though the gigantic
number of data obtained have not been fully analysed yet some
remarkable features are already worth mentioning. Female plants
showed no changes in sex expression during the observation period :
among the several thousands of described flowers from ca. 300
plants only one showed stamens, all others having well-developed
ovaries, and nearly free corollas but lacking completely male sex
pans. Male flowers were only slightly variable with respect to the
tube/lobe ratio. Hermaphrodite plants appeared highly variable for
all characters under consideration. Both, the variability between
and with in families was very striking. Besides, the sex
expression of individual plants changed from week to week.
There are strong indications that soil conditions greatly affected
sex expression. For instance hermaphrodite plants of progenies from
all combination types tended much more to femaleness at wide than
at narrow spacing.
Segregation ratios for the combinations FxM, FxH3, FxHi, H2 selfed
and H3 selfed did conform to the expected ratios based on the
hypothesis of Storey and Horowitz. However, marked deviations from
the hypothetical ratios were found for the combina tions Hi
selfed, HixM, HoxM and to a lesser degree for HixH3. In all these
cases the number of hermaphrodite plants obtained surpassed the
expected value.
8.2. INHERITANCE OF SOME SEED COAT CHARACTERISTICS IN Vigna
ungmculata (L) WALP. (70/12)
The investigations into the inheritance of the seed coat colour and
the seed coat pattern were continued. Special attention was paid to
the nature of intensity gradations of "Watson", variability in the
"Holstein" pattern, and to difference in size of "large eye" and of
the concomitant degree of speckling. Besides, the segregation of a
new pattern type "dark brown mottled" was analysed.
Progenies resulting from seeds classified as "dark" or "very dark"
Watson were uni-
21
formly dark, whereas descendants from "normal", "light" or "very
light" Watson se gregated into lighter and darker types. At least
two intensity genes are thought res ponsible for this variation.
In a similar way, Holstein parents having more than 50% of the seed
coat surface coloured, remained constant for this characteristic ;
variegated seeds with large uncoloured areas, however, segregated
in several Holstein types. Again the results could not be explained
by the action of a single modifying gene.
Even more complicated appears the analysis of the characters "eye"
and "speckling". The classification of seeds into "large eye" and
"medium eye" was particularly impeded by the differences in seed
size. Nevertheless there are strong indications that there are
genetical differences between medium eye and large eye. As for
speckling it was found that this is highly correlated with eye
size. Medium-sized eyes are seldom accompanied by large numbers of
speckles; besides the speckles found are generally small. "Dark
brown mottled" segregated into the parental type and solid brown,
and the new patterns "dotted brown" and "mottled-dotted brown" ;
mottling is monogenic dominant over non-mottling. The absence of
both Holstein and Watson in the progeny is surprising. An
explanation might be that the parents were homozygous for both W
and H but heterozygous for the recessive epistatic dotting factors
Di-di and I V d i In the first generation upon self ing 1/16 of the
progeny will have the homozygous recessive con dition dididâdï and
therefore be "dotted". Future work will have to prove this.
22
9. HORTICULTURAL AND AGRICULTURAL HAND-TOOLS
This research comprises a comparison of traditional and newly
introduced hand-tools that can be used in agriculture and
horticulture in, Surinam. Basically the performance and the
physical work load of the subject of experiment during work and the
quality of this work are being compared for different tools.
However, because of the simple device for measuring the work load
this research can only provide a general impression.
During the long rainy season a comparison was made of the scythe
and bush-knife (71/10). The work carried out (by fuil-grown men)
was mowing grass vegetations of different ages. In young grass a
scythe of 60 cm blade lenght was used, in old grass cne of 35 cm.
The latter has a greater solidity and is therefore more suitable to
mow the firmer stems of old grass. The bush-knife had a blade
length of 54 cm and was used in young as well as old grass.
A 10 m swath was mowed in one run. The quality of the work,
especially the stubble length, was about the same for the different
tools.
In young grass the scythe appeared to perform better and was less
tiring than the bush-knife. In old grass the differences were less
marked. It may even be possible that the use of a bush-knife in old
grass is preferable to that of a scythe.
In the long dry season a comparison was made of weeding tools in a
crop of maize on a heavy sandy clay (71/10, 71/26). The row
distance was 90 cm. The following tools were used : a traditional
hoe, a long handled hoe, a scuffle hoe and a cultivator. Their
measurements and weights are presented in Table 5. Many remainders
of the last crop such as stems and roots were in the ground, which
had an adverse effect on the results (Table 6).
Due to the many remainders in the soil the use of the scuffle hoe
resulted in a rather high work load and small performance. The
cultivator was hindered least by these remainders. In spite of the
highest work load the number of workpulses per m2
for the cultivator was lowest of all tools. Also the quality of
weeding was assessed (Table 7). It seems that with one tool
all types of weed were killed rather well, while another tool only
killed broad-leaved weeds. However, more work is required to
confirm these differences.
Table 5 - Measurements (cm) and weights (kg) of the various
tools
, handle blade working . , t oo ! length width width w e i«h
t
traditional hoe long handled hoe scuffle hoe cultivator (5
tines)
100 165 170 170
23
Table 6 - Performance and work load of the subjects of experiment
during the work with the various tools
tool
work- pulses per m2
31 33 37 44
17.22 18.16 22.68 13.99
32.0 31.0 32.5 32.8
77 77 70 67
•) "Workpulses" are defined as the difference between the number of
heart-beats during work and at rest.
Table 7 - Quality of weed control expressed as the percentage of
surface covered by weeds and as weed dry weight, 14 days after
weeding
quality of weed control traditional hoe
longh. hoe
14 days after weeding
15.8 11.2 14.6
25.9 18.1 25.2
30.8 25.0 30.0
28.3 20.9 31.4
weed dry weight 14 days after weeding (g per m2) 6.6 11.5 15.2
16.3
The overall impression is that the traditional tools in Surinam
agriculture (hoe and bush-knife) did not fall short of the
expectations and performed very well in com parison to the newly
introduced ones.
24
10.1. MEASURING RAINFALL AT DIFFERENT LEVELS (70/22)
Rainfall measurements in a standard raingauge at 1.50 m above
groundlevel are compared with measurements in a selfrecording
groundlevelgauge. The latter has been briefly described in the
previous annual report (CELOS Bulletins, 13, p. 29).
Only four times out of a total of 44 a difference per decade
occurred of more than 1 mm; the decade levels varied from 45.1 tot
144.8 mm. The maximum difference per decade was 3.4 mm, which was
observed on a total of 144.8 mm recorded in the standard raingauge.
Generally differences per decade were below 2%. Over a period of 12
months in which a total of 1959.7 mm was recorded in the standard
raingauges the difference amounted to only 5.0 mm.
Daily totals and decade totals over a period of almost 18 months of
registration were statistically compared using a Student-test. In
neither case significant differences were found.
From this study it may be concluded that the use of a standard
raingauge at 1.50< m above groundlevel, does not lead to
systematic inaccuracies when recording rainfall in the coastal area
of Surinam.
10.2. THE DETERMINATION OF ÉVAPOTRANSPIRATION WITH A WEIGHABLE
LYSIMETER
(70/23)
Except for rice, relatively little its known about the exact
magnitude of the évapo transpiration of crops in Surinam. A
knowledge of the évapotranspiration may be desired in connection
with irrigation proposals, water budget studies etc. Lysimeters are
the only instruments that can be used to make a direct measurement
of the évapo transpiration. The weighable lysimeters currently
used are weighed on the basis of various principles using different
techniques.
At CELOS the hydraulic loadcell technique was chosen on account of
its simplicity and, as reports in the literature indicate, its
dependability. The lysimeter consists of an inner tank 1.80 m long,
1.50 m wide and 1.30 m deep, made of 6 mm steel plate, with
internal strengthening of 4-cm I-beams. This tank fits, with only a
few centi metres tolerance around, into a cellar with a reinforced
concrete floor and walls of which the upper 0.62 m consist of 6 mm
steel plate. Both cellar and lysimeter tank are watertight and are
provided with drainage facilities. The lysimeter tank will be
carefully refilled with the original soil, which consists of
approximately 1 m heavy clay overlying fine sand. At the bottom of
the tank a sloping concrete floor has been constructed on which a
few thin layers of filter sand are placed to facilitate the drain
age of percolating water. The amounts of run-off and percolating
water are collected in reservoirs in which the waterlevel can be
determined.
25
The weighing system consists of two interconnected hydraulic
loadceils made of nylcn-butylrubberpipe*, an inverted-U-tube type
manometer and a third loadcell. All loadceils are filled with water
to which some Q1SO4 (0.5%) is added as an algae in hibitor. The
lysimeter rests by means of two wooden blocks (Greenheart, Tabebuia
serratifolia (VAHL) NICHOLSON) on the rubber loadceils. Pressures
in the latter, which vary with the weight of the lysimeter, are
measured in the manometer. Pressure offset is obtained with the
third loadcell on which a constant load is applied by means of a
lever. This compensating loadcell is placed in a second underground
cellar which is in open connection with the lysimeter cellar. The
manometer is placed above gxoundlevel at about 4 m from the
lysimeter. Pressure differences are converted to depth of evapo
ration on the basis of the ratio of total evaporating surface to
bearing surface of the wooden blocks.
During the year under review construction proceeded to such a point
that the lysi- metertank was placed on the loadceils and that the
manometer system could be tested.
10.3. DRAINAGE BY MEANS OF PLASTIC TUBING — AN INVESTIGATION INTO
THE POSSI BILITIES OF SUBSURFACE DRAINAGE IN THE COASTAL AREA OF
SURINAM (70/24)
A drainage experiment was initiated at CELOS in order to
investigate the possibili ties of subsurface drainage of a heavy
clay soil of the Surinam coastal plain.
The construction of the trial field, which has been described
earlier (CELOS Bulle tins, 13, p. 30), was finished during the
year. After the field had been leveled, kudzu (Pueraria
fhaseolokles (ROXB.) BENTH.) was sown.
In short it comprises five treatments, arranged in a randomized
block design with three replications; each treatment consists of
five drainconduits of 50 m long and at 4 m intervals. Discharge
measurements were started soon after completion of the trial field
and were carried out whenever possible. The rate of outflow of the
five indivi dual rubes in each plot is determined simultaneously ;
this is done by catching the water into calibrated buckets.
On account of high-intensity showers of short duration, which are
common in Suri nam, the hydrograph of the plots mostly shows a
peak very soon, i.e. 15-50 minutes after the discharge starts. The
latter commences from 8 to 20 minutes after the be ginning of a
shower of sufficient intensity and duration. The outflow seldom
continues for more than 8 hours after it stops raining. It is
therefore essential to start measuring as soon as possible after
the beginning of a shower. Often it was not possible to measure the
rising limb completely. A recording rainauge (see 10.1) makes it
possible to compare the hydrographs with the intensity-duration
curve of the rainfall.
The total discharge of each plot can be found by computing the area
under the hydrograph and is expressed as a percentage of the
precipitation.
So far only a limited number of successful measurements have been
obtained. They indicate that tubes without coarse sand envelopes
give better results, i.e. a faster res ponse than the same kind of
tube in sand. Corrugated tubes give somewhat higher discharges than
smooth ones ; the percentage discharge varied between a high 80%
for corrugated tubes and a low 20% for smooth tubes in sand. At
times the discharge of plots without sand envelopes peaked at 6
mm/hr.
* Carlisle Corp., Carlisle Pa. USA, distributed by Watersaver Co.
Denver, Colo., USA.
26
10.4. A WATER BUDGET INVESTIGATION AT CELOS (71/9)
The greater pan (15.6 ha) of the CELOS grounds forms a polder which
is suited to set up a water budget study. Such a study can be very
useful, especially in connection with the lysimeter experiments
(see 10.2). Moreover a water balance may yield a better insight
into the distribution of rainfall over run-off and
infiltration.
The various components to be determined for a water budget are :
precipitation, evaporation, discharge, seepage and the change in
the amounts of water stored in both soil and open water. Discharge
and seepage may be positive or negative, meaning outflux or influx
respectively. Negative discharge occurs when water is pumped into
the polder for flood or sprinkler irrigation.
The period during which measurements were taken was from June 4 to
August 13 ; this was during the wet season. Accordingly 659 mm of
rain were registered during this period. By placing a propeller
type flowmeter in the outflow pipe of the drainage pump it became
possible to measure the (positive) discharge. The amounts of
irriga tion water were computed from a registration of the running
hours of the irrigation pump. Underground flow was estimated from
groundwater observations which were carried out regulaily inside
and outside the test area. The amounts of water stored in the soil
were determined regularly by taking core samples, whereas the
storage in open water courses was calculated from waterlevel
registrations. As turned out later the moisture sampling had not
been carried out with sufficient intensity so that a waterbalance
per decade became questionable. Over the whole period, however, the
accuracy was satisfactory.
Evaporation was computed by means of the Penman method but for
comparison only, since evaporation was considered to be the unknown
factor in the balance. The most interesting conclusion that may be
drawn from this study is that évapotrans piration as computed from
the water budget is considerably lower (about 25%) than the
évapotranspiration computed according to Penman's method. Over the
entire 70- day period the évapotranspiration was found to be
approximately 200 mm whereas Penman's method yielded about 270
mm.
27
31.1. A MARKETING STUDY OF VEGETABLES ( 7 1 / 24 )
As part of an overall srudy of the production and marketing of
fruit and vegetables in Paramaribo and its surroundings (see
section 5), an investigation of the marketing structure was
initiated in October of the year under review, to obtain
information on : (i) the sales and profits of the different kinds
of wholesaler (commission-agent,
middlemen etc.) (ii) the sales and profits of the retailers at the
capital's Gentral Market ; (iii) the farmer's position in selling
his products; and (iv) the extent to which Government is involved
in the present structure.
For one month observations were made of and talks held with the
directly and in directly involved persons at the Central Market
during wholesale hours (23.00-08.00 h). The data thus obtained have
been checked and rechecked before being processed, after which the
work will be repeated to be ab)le to confirm conclusions. At the
same time about 50 retailers out of a total of 400 were interviewed
during a 2-month period about the prices they paid, the amounts
they bought, the time they bought at, and the persons they bought
from. Where possible the quality of the products was noted. From
these data and from consumer prices collected by the Ministries of
Agriculture and Economic Affairs the range of profit margins can be
worked out.
As to the farmer's position in selling his products conclusions
cannot be drawn until the farm management study has been
completed.
To study to what extent Government is involved in the marketing
structure reports are being collected and talks held with officials
of the above mentioned Ministries.
11.2. AN INVESTIGATION OF THE CONSUMPTION OF FRUIT AND VEGETABLES
IN PARAMA RIBO AND ITS SURROUNDINGS (71/27)
Since an analysis of the problems of the marketing of fruit and
vegetables is not complete without taking into account the consumer
an investigation was started into the consumer's behaviour in
relation to these commodities.
Only supplementary information was collected. In the years
1968-1969 a fairly thourough budget study has been carried out, the
data of which provide most useful information for the investigation
referred to. The supplementary data were collected for those
population classes that had not been covered by the sample for the
budget study.
The investigation was commenced with two classes, viz. the
high-income group and the families the head of which was
unemployed. Adding these two classes resulted in a coverage of
about 96 percent of the people in the population area.
Because of lack of alternative sources like income tax data, the
sample for the high- income group was obtained from the telephone
directory ; nearly every subscriber has
28
an income of above Sf. 6000 per year. The sample for the group of
unemployed was obtained through the employment bureau.
Every month about 24 families in each class are interviewed daily.
If the inter viewed so wish they can write down the information
themselves, the forms being collected twice a week. The questions
asked are about prices paid, quantities bought and the places they
bought. At the last day of the period of interview the consumer U
asked about his income and the size of his family.
To obtain the first sample of 24 families in the "unemployed"
group, 69 addresses were needed. Nineteen refused co-operation ; of
the remaining 26 either the addresses proved wrong or the people
could not co-operate for other reasons.
The sample for the high-income group was obtained by telephoning.
Response here was good.
29
12. PLANT BREEDING
12.1. FRUIT SETTING IN SWEET POTATO, Ipomoea batatas (L.) LAM.
(69/17)
Investigations concerning the role of sterility and incompatibility
mechanisms in reducing fruit setting in sweet potato are in
progress since 1969. In the year under review special attention was
paid to the compatibility relations between various clones.
12.1.1. FIELD INVESTIGATIONS
A number of new clones entered the incompatibility programme viz.
Copperskin Goldrush, Louisiana 3 and Louisiana 5 from the U.S.A.,
and Pono Rico, Putri Selatan, and Tox Paars from Indonesia. Also
some additional material of Genjem 1 and 2 was introduced for
comparison with earlier introductions the purity of which was
doubtful. In addition some 80 Fi plants came in the field.
About 15,000 pollinations were made, 6,000 of them being
intervarietal combinations; the remaining 9,000 were selfings of Fi
plants or backcrosses to the parents. Of the parental crossings
only ca. 120 fruits, containing 150 seeds, were obtained.
Considering the fact that these fruits were derived from 70
parental combinations it will be clear that in most cases
percentages of fruit setting were very low. This once more stresses
the important role played by sterility factors. The idea as
expressed by MARTIN & CABANILLAS (1968)* that once the
sterility components have been identified the in compatibility
might appear to be only an ignorable relic in relation to seed
setting, is likely to be true.
Another complicating factor in determining the compatibility
relation lies in the weather conditions. Certain combinations that
were somewhat compatible at one mo ment completely failed to give
seed setting some weeks later. Particularly showery weather seemed
very unfavourable.
Fruit setting percentages have not yet been computed for the
various Fi selfings and backcrosses. But, with the exception of a
small number of very productive plants, the results were similar to
those of the parental combinations.
In 1971 as well as in 1970 a correlation was found between seed
weight and emergence. No emergence occured if seeds weighed less
than 10 mg, while values of nearly 100% were found for seeds of 20
mg or more.
The germinative power also appeared to be affected by the maternal
parent especial ly in the range 10 to 20 mg. Some of the seedlings
from light seeds died immediately after emergence.
12.1.2. RELATIONS BETWEEN STYLE AND POLLEN
The study of pollen germination and pollen tube growth using the
fluorescence technique, which had to be interrupted at the end of
1969, was continued in the year un-
• MARTIN, F. W. & E. CABANILLAS, 1968. Classification of sweet
potato varieties for compatibility and sterility. Proc. Am. Soc.
bort. Sei. 93: 502-511.
30
der review. The work completed so far concerns all combinations
having one of the clones Djarak, Willemsrank, Blauwkop, Hopi, USA
130, White Star, Butikatoka, Brokopondo, and A 138 as maternal
parent Analysis is greatly hindered by the large variation both
within and between combinations that occurs in the number of pollen
grains sticking to the stigmatic surface. Nevertheless some general
conclusions can be drawn : (i) the number of germinating pollen
grains seldom surpasses 50%, (ii) the number of pollen tubes
penetrating the stylar tissue generally lies between 1 and 10,
(iii) the number of tubes reaching the midstyle or even the
micropyle four hours after pollination is very sinall. Concerning
this point it has to be noted, however, that it often was very
difficult to trace the pollen tubes in the stylar tissue nearby the
ovary.
12.2. CYTOPLASMIC MALE STERILITY AND FERTILITY RESTORATION IN
SORGHUM,
Sorghum bicolor (L) MoENCH (69/23)
As stated in CRT .OS Bulletins, 13, p. 33. a project was started
"to trace the response of some widely accepted hybrids and their
parents to Surinam conditions, and to ana lyse the genetical
constitution of the various cultivars for their fertility
characteristic".
In the 1970-experiment Martin and CK 60A had been used as the
sterile parents, Tx4l4 and Texas 7078 serving as restorer lines for
both of them. The segregation ratios obtained (F2 "> 15: 1 ; Bi
</> 2 : 1 ) suggested a more complicated inheritance than
advanced by MAUNDER & PICKETT (1959)* and Pi & Wuu (1963)*.
Since little attention was paid to the degree of fertility, the
experiment was repeated in 1971, using 35 progenies of the types
(MSxR) selfed, MS x (MSxR), and [MS x (MSxR)] selfed. Each progeny
consisted of two rows of about 50 plant hills. As a result of large
differences in emergence, the number of plants per family varied
from 40 to more than 100. Heads were bagged just before onthesis,
evaluated for seed setting 14 days later, and then cut off to
stimulate outgrowth of the tillers and side stalks. According to
the amount of seeds set, heads were classified as — (no seeds at
all), (—) less than 10 seeds per head, ± (less than 20% seed
setting), (-|-) (20-70% seed setting), -f- (over 70% seed setting).
Of each plant a maximum of eight heads will be evaluated.
Results obtained so far again indicate that more than one
chromosomal factor plays a role in the restoration of fertility. In
some genotypes an effect of environment on fertility expression was
evident: successive heads of the plants concerned changed from
partially fertile to sterile and vice versa.
As evaluation is still in progress segregation ratios have not yet
been computed.
12.3. BREEDING SYNTHETIC VARIETIES IN MAIZE, Zea mays L
(69/24)
In I969 a programme was initiated (i) to develop synthetic
varieties as an alter native to the production of hybrid varieties
and (ii) to compare different breeding methods for obtaining
synthetics. Large numbers of introductions have been obtained since
and many of them have been scrutinized for their suitability as a
component in a synthetic variety.
MAUNDER, A. B. & R. C. PICKETT, 1959. The genetic inheritance
of cytoplasmic-genetic male sterility in grain sorghum. Agron. ].,
5 1 : 47-49. Pi, C. P. & K. D. Wuu, 1963. The inheritance of
cytoplasmic genetic male sterility in sorghum: Bot. Bull. Acad.
Sin., 4 : 15-22.
31
During 1971 two groups of introductions were re-observed and
selected, viz. (i) 104 Caribbean composites from the Centra
Internacional de Mejoramiento de Maiz y Trigo (CIMMYT), Mexico
City, and (ii) 82 inbreds (le) extracted from two Central American
composites, that were handed over by the Agricultural Experiment
Station, Parama ribo. Individual plants were recorded for general
performance, number of days to tasseling and silking, plant height,
circumference of the stem, ear number, ear length, mid-ear
circumference, grain insertion, and weight, colour and shape of the
kernels. Tassels and ears were bagged prior to flowering and plants
were selfed or crossed within a line or composite.
Average plant height was over 200 cm for nearly all CIMMYT
composites; most stems were firm and reached circumference values
of 7 cm or more. Though there was a considerable variation in ear
and grain characteristics, some general features can be summarized
: (i) ears large, thick, and well-filled, (ii) grain insertion
often irregular, (iii) grains large, alabaster white or ivory, more
or less dent, sometimes shrinking and/or sensitive to bolting. As
to ear length and circumference variation appeared to be large. Ear
length varied from 10.9 to 21.8 cm, ear circumference from 10.6 to
17.2 cm. The distribution of average ear length and circumference
for both CIMMYT composites and Central American inbreds is shown in
Table 8.
As may be expected the average values are much smaller for the
inbred lines, vary ing from 9.3 to 16.3 for ear length and from 90
to 13.4 for ear circumference.
Table 8 - Frequency distribution of average ear length and average
ear circumference classes for CIMMYT composites and Central
American inbreds
class (cm)
CIMMYT
length
104
composites
circumference
— — — —
— — — — — 82
circumference
— — — — — — — — 71
As found in 1970 the lines differed largely in average plant height
- from about 100 to far over 200 cm -, and number of ears per
plant. Seed charateristics were quite uniform and included : (i)
orange or yellow kernel colour, (ii) regular insertion, (iii)
scarse occurence of dent type kernels, and (iv) small kernel
size.
32
-S:
's
5
Studying root systems of Caribbean pine.
Many of the "lines" appeared not pure at all ; they were discarded,
or only the most promising ears were saved.
Progenies of the top-cross and polycross tests of 1970 were sown in
randomized blocks. Two replicates were planted on heavy clay soil
at the Centre's grounds and four on a sandy loam at the
Experimental Citrus Plantation Baboenhol, ca. 80 km south of
Paramaribo. Each block comprised 30 plots viz. 10 progenies from
each, the polycross, the non-emasculated top-cross, and the
emasculated top-cross. The plots consisted of 6 rows of 15 plants
spaced 30 x 90 cm. The two outer rows and two plants on both ends
of the remaining rows served as guards, leaving 45 record
plants.
Split application of fertilizer was used in all blocks. The
replicates on clay received two equal doses of a complete
fertilizer (400 kg/ha NPKMg—10+15+20+2), viz. at sowing and just
before tasseling, and an extra nitrogen top-dressing of 120 kg/ha
or urea 5 weeks after sowing. The blocks on sandy loam received
three times the above amount of complete fertilizer.
Replicates on clay grew well and no conspicuous decay of the
photosynthetizing organs was observed until the ripening stage.
Plot yields were from 4870 to 8420 g, corresponding with 4000-6930
kg/ha. Of two lines polycross as well as the top-cross progenies
yielded distinctly more than all other progenies. Great conformity
as to the order of yields was found for the two top-cross
procedures, but polycross pro genies were quite different in this
respect.
As a result of low and ill-distributed precipitation and heavy
borer attack, growth was poor for the blocks on sandy loam. Large
within-block variation occurred with respect to number of surviving
plants, ears per plot, and plot yield. Even when com puting the
yield on a basis of 40 plants/plot, i.e. the mean value found in
the clay replicates, average yields were 3-4 times lower than on
clay soil. At first sight no clear line could be traced as to the
sequence of yields of the various objects. The re sults of
statistical analysis were not yet available at concluding this
report.
33
13. PROTEIN IN FOOD CROPS
For an introduction to this multidisciplinary research project,
dealing with protein content arid protein quality in some major
tropical food crops, the reader is referred to the annual report
for 1969.
The experiments started in 1969 and 1970, and outlined in the
previous annual report, were continued or not yet closed in the
year under review. Again, however, progress was hampered by the
difficulties met in having the samples analysed. It is hoped that
with the recent completion of the Centre's own chemical laboratory
this problem has become a thing of the past.
As yet no conclusions could be drawn from the preliminary trial
(69/34) conducted in 1969 and 1970 to learn whether drying of
tubers of sweet potato and grains of maize, sorghum and cowpea at
relatively low temperatures (viz. 45, 65 and 85 degrees
centrigrade) causes decomposition of proteins
The same applies to an experiment (70/1) concerned with the
question whether the protein content and protein nutritive value of
sweet potato tubers are affected by variations in growing season,
fertilizing and age at harvesting. Field work in this trial came to
an end in 1971.
Additional samples were collected, and sent abroad for chemical
analysis, as a part of the investigations dealing with the relation
between protein content and quality on the one hand and plant
density (70/30) as well as type of variety (70/31) on the other
hand.
34
14.1. NATURAL REGENERATION
The research on this subject is mainly carried out in two projects,
viz. 65/3 and 67/9. The first one concerns a field trial laid down
in relatively lightly exploited high rainforest, and consists of
two adjacent blocks of 10.88 ha, each with a different refinement
as first treatment, i.e. poisoning of weed trees with diameter
limits of 10 and 20 cm respectively. In each block 6 treatments are
being compared in 8 repli cations. They comprise liberations of
valuable poles with a girth above 100 mm, applied at different
times over a period of 12 years. This year the usual records were
taken, but treatment was delayed ; it will be done next year. No
important changes in girth or height increment were found.
The second project (67/9), an experimental plot with 25 subplots of
1 hectare each, was laid down in 1967 in exploited high rainforest
at Mapanecreek. The experiment has already been described in former
annual reports. At last year's recording, as es- pected, the
liberated plots showed a marked girth increment upon treatment (a
mean girth increment of 25-45 mm per year). Trees in untreated
plots grew at a mean rate of 8-12 mm girth increment.
A remarkable decrease in increment was noted for the period
1969-1970 for most of the trees measured. This decrease is most
likely the result of the exceptionally dry weather in the second
half of 1969.
14.2. PLANTATIONS
Since a few years research is being carried out on the morphology
and develop ment of the root systeem of Pirtus caribaea MoRELET
(66/2). Some results of root studies of 8 and 12 months old pines
have already been mentioned in a former annual report. In the year
under review some root systems of trees of 10 years and elder were
excavated and drawn. A conspicuous characteristic of the root
system is the marked separation between horizontal and vertical
roots, which according to the literature appears to be normal for
pines. Though the deepest roots were not reached by excavation, it
is assumed that with trees of this age on well-drained loamy soils
some thin roots may reach depths of 3-4 m. Differences in
development of vertical roots, especially the taproot, between
dominant and suppressed trees were not as evident as those of
horizontal ones.
A number of rootgrafts (apparently resulting in callus growth on
stumps) was found. Grafting was observed only where roots met that
were some centimetres thick, or where a thin root was squeezed
between bigger ones. It may be that these grafts play some role in
the spreading of the unidentified root rot in pine plantations that
locally results in the death of trees.
35
15. SOIL AND CROP ANALYSIS
15.1. THE INFLUENCE OF EXPERIMENTAL CONDITIONS ON THE DETERMINATION
OF CATION EXCHANGE CAPACITY AND EXCHANGEABLE CATIONS ( 7 1 / 2 5
)
At the close of 1971 the chemistry laboratory was nearly finished.
However before routine analyses can be done, it is to be decided
what procedures are to be followed. This is especially important
for chemical analysis of soils, since the meaning and
interpretation of results largely depend on the method used.
The ammonium acetate method, particularly the percolation
procedure, was chosen for the determination of cation exchange
capacity (CEC) and exchangeable cations.
Mixtures of quartz sand and the soil to be analysed are brought in
percolation tubes and extracted successively with ammonium acetate,
ethyl alcohol and calcium chloride. To select a procedure that is
correct, simple, cheap and appropriate for as many soils as
possible, the effect of the following variables is being examined :
1. Concentration of ammonium acetate : 0.5, 1.0 or 1.5 N 2. Amount
of quartz sand with which the soil is mixed: 20, 50, 80 or 110
grammes; 3. Texture of quartz sand : coarse (unsieved) or finer
than 600 microns ; 4. Amount of soil : 10, 25 or 50 grammes.
To start with two soils were used : a heavy clay and a loamy coarse
sand. So far it was found that a concentration of 0.5 N ammonium
acetate is too low
and that for the clay soil fine quartz sand is required. The work
continues.
36
16. SOIL FERTILITY AND PLANT NUTRITION
16.1. THE USE OF MAIZE (Zea mays L) FOR THE ASSESSMENT OF
SUFFICIENCY QUO TIENTS (71/21)
Based on research in Australia (BOUMA, 1965*), a pot experiment
technique has been developed for quick identification of the
nutrients that are in short supply in soils (JANSSEN, 1970*). In
these experiments, which take about three weeks, the follow ing
procedure is used. A small pot with a gauze bottom is filled with
the soil to be investigated and placed on a container with a
nutrient solutioa Seeds are sown in the soil. After the roots have
appeared through the gauze and have reached the nutrient solution,
the plants can take up nutrients from both soil and solutioa If a
nutrient is omitted in the solution, plants take up that nutrient
from the soil only. In case of rich soils plants grow almost as
well on a deficient solution as on a complete one ; however, if the
soil is poor plant growth on a deficient solut'on will be
retarded.
The availability of a particular nutrient in the soil is indicated
by the "sufficiency quotient" (SQ), i.e. the ratio between the
relative growth rates (RGR) of plants on deficient and those on
complete solutions (e.g. SQN for nitrogen). SQ depends not only on
the availability of the studied nutrient, but also on the length of
the time interval over which the relative growth rates are
measured.
Until recently there was no experience in this type of experiments
with maize, a crop that appears very suitable under Surinam
conditions. Hence a preliminary experiment was started to gain some
experience and to establish the most appropriate time interval to
assess relative growth rates. The experiment was carried out with
three soils that were expected to differ widely in fertility, and
comprised the nutrients N, P, K, Mg, Fe and Cu.
The interval between 9 and 17 days after sowing, i.e. between the
four and eight- leaf stages, proved most appropriate for relative
growth assessments and calculation cf SQ. The finer the soil
texture the higher SKN and SQK- SQP was about the same on two soils
and somewhat higher on the heaviest one. No shortage of Mg, Fe and
Cu could be detected. There was a close correlation between plant N
and SQN and between plant K, SQK and soil exchangeable K.
It was concluded that maize is suitable for this type of pot
experiments, at least as far as they concern the detection of
deficiencies of the main nutrients N, P and K.
• BOUMA, D., 1965: Growth changes of plants following the removal
of nutritional stresses Thesis. Wageningen.
JANSSEN, B. H., 1970 : Soil fertility in the Great Konya Basin,
Turkey. Arg. Res. Rep., CLD. Pudoc, Wageningen.
37
16.2. A STUDY OF THE NUTRITIONAL STATUS OF Pmus Caribaea MORELET BY
MEANS OF THE TECHNIQUE USED FOR THE ASSESSMENT OF SUFFICIENCY
QUOTIENTS (71/22)
Some growth difficulties of Pinus caribaea MORELET on the sandy
soils in the Surinam interior are thought to be caused by shortage
of nutrients. Since it is difficult and very laborious to establish
in field trials the nutrients that are involved, it was thought
worthwhile to investigate the possibilities of the pot experiment
technique as des cribed above. It was hoped that some of the
deficiency symptoms of the plants on incomplete solutions resemble
the field phenomena, thus enabling an identification of the
nutrients in short supply.
Young Pinus plants were transferred with soil from nursery bags to
pots with a gauze bottom. The pots were placed on containers with
different nutrient solutions : complete solution or solutions
without N, P, K, Ca, Mg, Fe, B or Cu, respectively.
Very clear deficiency symptoms were obtained on the solutions
without N, P, Mg, Fe or B. Less distinct were the responses to K,
Ca and Cu.
The experiment is still in progress.
16.3. A SOIL FERTILITY SURVEY OF SOME SOILS IN THE INTERIOR OF
SURINAM (71/28)
The results of the greenhouse experiments mentioned in section 16.1
need to be checked in the field on soils that vary widely in
fertility. Until now little is known about the fertility of the
Surinam soils. Though there are soil maps, it often is rather
hazardous to use these for information on soil fertility. The
criteria important for crop production cannot always be included in
a soil map legend, either because it is impossible for them to be
recognized in the soil profile or because the soil properties
decisive for crop production are not known. A study on the relation
between soil type and soil fertility appears therefore
desirable.
Such a study has been planned for those Surinam soils that also
occur in large areas elsewhere in the tropics. Since it is not
possible to include all units concerned, the actual research is
preceded by a survey to find out where the most interesting soils
are, entailing chemical analysis of crop plants from trials and
plantations, and the carrying out of small fertilizer trials.
The study started in December of the year under review. Grain
samples were taken from sorghum at Baboenhol (70/28 ; section 17)
and from maize at CELOS and at Baboenhol (69/24 ; section 12).
Furthermore three field trials were laid dcwn on three different
terrace soils at Victoria, about 100 km south of Paramaribo along
side the Surinam river. Each trial comprises the treatments (i) no
fertilizer, (ii) 120 kg N/ha, (iii) 120 kg N + 90 kg P205/ha, and
(iv) 120 kg N + 90 P205 + 120 kg K2O + 12 kg MgO/ha. The crop was
maize.
38
17. TILLAGE
17.1. A COMPARISON OF TILLAGE AND ZERO-TILLAGE SYSTEMS ON HEAVY
CLAY SOILS FOR THE CONTINUOUS GROWING OF ANNUAL CROPS ( 7 0 / 2 5
)
The trial as described in the previous annual report was continued
in the year under review with rice and Crotalaria sp., grown in the
period March to August, and with maize and soyabeans from September
till December. (For details of the treatments che reader is refered
to CELOS Bulletins 13, p. 40.)
The emergence of Crotalaria sp., which was sown in 90-cm rows, was
very poor, probably because of the roughness of the seedbed and the
very wet weather conditions prevailing at the time of sowing.
Consequently this crop failed completely.
The rice (cv. Washabo), planted in 30-cm rows, was sown by hand in
the period 15-20 March. Emergence and subsequent growth were good.
Fertilizing took place on 8 April and on 15 May at rates of 250 kg
NPK (15+15+15) and 85 kg urea per hectare respectively. The crop
was harvested between 10 and 15 August, and threshed mechanically
following some drying in the field. Some of the effects of the
treatments on growth and yield are presented in Table 9.
Table 9 - Tillage operations and plant growth (rice, cv.
Washabo)
rotavating ploughing zero-tillage
weed control (h/ha) plant height on 15 May (cm) yield at 15%
moisture content (tons/ha)
The large number of hours required for weed control was caused by
bad weather conditions and the presence of sedges (Cyperus spp.).
Weeds were controlled by hand hoeing.
Tillage for the second period of occupation started at the
beginning of September. The crops were sown mechanically on 8
September, maize being planted in 90-cm rows, soyabeans in 45-cm
ones. Fettilizer was applied at the end of the month at rates of
250 kg NPK (15 + 15+15) and 250 kg NPKMg (10+15+20+2) per hectare
for maize and soyabeans respectively.
Although the seeds were correctly placed, the emergence of the
maize was only moderate in all treatments, and that of the
soyabeans poor in the tilled treatments. Inadequate moisture supply
and a very loose soil may have caused the poor per- formanse of the
soyabean seed.
Weed control was by hand hoeing. The maize was sprayed once with
Dipterex SP 95 against Laphygma frugiperda. Though the soyabeans
were rather heavily attacked by Cerotoma variegata, control
measures were not considered necessary.
The soyabeans were harvested by hand at the end of December, the
maize at the beginning of January 1972. Both crops were threshed
mechanically. Conditions for threshing were not ideal, however.
Moisture contents of the cobs and pods were high, there being no
facilities for artificial drying. Some effects of the treatments on
the growth and yield are presented in Table 10. Overall yields were
lower than usual, which may partly be caused by insufficient care
during the first weeks after germi nation.
39
Table 10 - Tillage operations and plant growth (soyabeans and
maize)
soyabeans weed control (h/ha)
— no sedges present — sedges present
number of productive plants per metre row yields (ton/ha; 15%
moisture content)
maire weed control (h/ha)
— no sedges present — sedges present
number of productive plants per metre row yield (tons/ha; 15%
moisture content)
rotavating
257 670
3.3 1.03
450 420
3.0 3.18
Because of the poor emergence of the soyabeans and the resulting
low plant densities it is not possible to relate the yields to the
tillage systems.
As for maize, though ploughing gave the best yield, it is not
statistically different from the other two.
17.2. A COMPARISON OF TILLAGE AND ZERO-TILLAGE SYSTEMS ON SANDY
LOAMS FOR THE CONTINUOUS GROWING OF ANNUAL CROPS ( 7 0 / 2 8
)
In January 1971 a field trial was started to investigate (i) the
tillage systems for annual crops when continuously grown on sandy
soils, and (ii) the response of the crops, the weeds and the soil
to these systems.
The lay-out of t