EFPECTS OF PLANTING DATE, SEED SIZE-DENSITY AN-D PLANT
POPULATION ON GROWTH AND REPRODUCTION OF
TWO CULTIVARS OF COWPEA
Famara Massaly
A Thesis
Submitted to the Faculty of
Mississippi State University
in Partial Fulfillment of the Requiremenk
for the Degree of Master of Science
in the Department of Agronomy
Mississippi State, Mississippi
December 1991
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EFFECTS OF PLANTING DATE, SEED SIZE-DENSITU AND PLANT
POPULATION ON GROWTH AND REPRODUCTION OF
TWO CULTIVARS OF COWPEA
BY
Famara Massaly
Approved:
Professor of Agronomy-Seed
Interim Head (Graduate
Coordinator of the Department of
(Chairman of Supervisory
Agronomy)
Commit tee and Director of Thesis)
William R. Fox
Profcssor of Agronomy-Sced
Dean of the College of Agriculture
Tcchnology
& Home Economies
(QL.44Gv&ti
. ’
&&?g(
Charles E. Vaughan
Professor of Agronomy-Seed
Professor Emeritus, Agriculture
Tcch IIOkJgy
& Biological Engineering
Richard D. Koshel
Dean of the Graduate Schoal

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Name: Famara Massaly
Date of Degree: December 18, 1991
Institutioii: Mississippi State University
Major Field: Agronomy (Seed Technology)
Major Professor: Dr. James C. Delouche
Titlc of Study:
EFFECTS OF PLANTING DATE, SEED SIZE-DENSITY, AND
PLANT POPULATION ON GROWTH AND REPRODUCTION OF
TWO CULTIVARS OF COWPEA
Pages in Study: 64
Candidate for Degree of Master of Science
The objectives of these studies were to establish the effects of planting date,
seed size-density, and population density in cowpea on vegetative and reproductive
development. The Mississippi Pinkeye and Mississippi Bunch Purplehull cultivars
were used in the studies on the MAI?ES Plant Science Farm in 1990/91. The
effects of planting date on growth and development of cowpea were primari1.y
environmental. Variation in major environmental factors (temperature, solar
radiation and water supply) among the planting dates significantly affected
seedling growth and the components of yield. Large-heavy seeds were much more
vigorous than small-light seeds and produced plants that yielded more those from
small-light seeds. Plants in low population communities (14 plants/3 mf produced
more biomass and yicld than those in the high population communities (60 plants’3
m), but the diffcrcncc in plant density between the low and high populations was
too great for thc compensatory response to equalize biomass production.
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DEDICATION
TO
The Living Memory of My Father, M. Massaly,
Without His Wisdom, Encouragement, Praises, Sacrifices,
1 May Never Have Been Able to Perform My Education
TO This Level
ii
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ACKNOWLEDGMENTS
First and foremost, Praise be given to the Omnipotent for giving me the
health, the opportunity and the strength to achieve this step of my education.
1 would like to thank my major professor, Dr. James C. Delouche, for his
support, suggestions, guidance, and counseling during the time 1 spent on m,y
program of study and towards the successful completion of this manuscript.
Special thanks to my committee members, Drs. C. H. Andrews, C. E.
Vaughan, and G. B. Welch, for their constructive criticism and signifïcant
contributions to my training program. Acknowledgments go to the staff and
students of the Pace Seed Technology Laboratory for all their assistance during my
stay here. 1 would also like to thank Ms. Catherine Thompson for typing the draft
copy of this manuscript and Ms. Shirley Barnes for typing the final copy.
Acknowledgements are extended to the Office of International Programs and
International Student Services for their constant support and suggestions.
Many thanks are expressed to the United States Agency for International
Development and the Agricultural Production Support Project (APS) in Senegal for
giving me the opportunity to participate in this training program..
1 wish to express my deepest gratitude to the Senegalese Institute of
Agricultural Research for allowing me to continue my education in the seed
technology area.
. . .
111
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Appreciation is expressed to my Senegalese friends, Alassane Bakhoum,
Kisma Wague and wife, and a11 African students for their supportive friendship
during this pcriod.
Special thanks are expressed to Ibrahim Mahamadou, Boukary I-Iama and
Ketty Paquiot for their considerable help during the harvests.
Last but not least, praises are given to my three favorite ladies (my mother,
my wife, Gnagna, and my daughter, Salimata) for their love, understanding,
patience, devotion and supreme sacrifices which helped me considerably during my
studies at Mississippi State University.
FM
iv
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TABLE OF CONTENTS
Page
DEDICATION
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . ,, . . . . . . . . . . . . . . . . . . iii
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . vii
CEIAPTEEI
1.
INTRODUCTION . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . 1
II.
LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Effects of Seed Size and Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
Field Emergence and Early Plant Growth
. . . . . . . . . . . . . . . . . .
6
Plant Growth and Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
Other Aspects of Seed Quality . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
Effects of Plant Population Density . . . . . . . . . . . . . . . . . . . . . . . . .
1 0
Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 2
III.
MATERIALS AND METHODS . . . . . . . . . . , . . . . . . . . . . . . . . . . . . 15
Time of Planting Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 5
Methods and Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 5
Weather Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
Seed Size and Density Experiment . . . . . . . . . . . . . . . . . . . . . . . . . .
1 7
Seed Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 7
Field Planting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 8
Rate and Percent Emergence . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 8
Dry Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 9
Seedling Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 9
Yield Components and Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 9
Weight of 100 Seeds . . . . . . . . . . . . . . . . . . . . .
,,. . . . . . . . . . . . 2 0
Weight of Pods Per Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 0
Weight of Seeds Per Plot
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 0
Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 0
Rate of Imbibition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 0
Seedling Growth Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 1
V

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CHAPTER
Page
Plant Population Density Study . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 1
Field Emergence and Survival . . . . . . . . . . . . . . . . . . . . . . . . . .
22
Seedling Dry Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 2
Plant Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 2
Flowering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 2
Yield and Yield Components . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
Number of Plants Per Unit Area
. . . . . . . . . . . . . . . . . . . . . . . .
2 3
Seed Size Distribution
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
Statistical Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 3
I V .
RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . , . . . . . . . . . . . . 24
Effects of Planting Date on Growth and Development
. . . . . . . . . . . 2 4
Seedling Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 4
Number of Flowers Per Plant . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 9
Pod and Seed Number and Weight Per Plant . . . . . . . . . . . . . . .
3 1
PodLength
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
PodandSeedYieldPerArea
. . . . . . . . . . . . . . . . . . . . . . . . . . .
3 2
Weight of 100 Seeds and Seed Size Distribution . . . . . . . . . . . . .
3 2
General Observation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
Seed Size-Density Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 6
Germination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 6
Seedling Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
Emergence and Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 9
Seedling and Plant Growth . . . . . . . . . . . . . . . . .,. . . . . . . . . . . . 4 1
Reproductive Development . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 4 1
General Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Plant Population (Seeding Rate) Effects . . . . . . . . . . . . . . . . . . . . . .
46
Seedling Emergence and Survival . . . . . . . . . . . . . . . . . . . . . . . .
46
Seedling/Plant Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Reproductive Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 8
Seed Size Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 4
General Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 4
V I .
SUMMARY AND CONCLUSIONS . . . . . . ” . . . . . . . . . . . . . . . . . . . 57
BIBLIOGRAPHY
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
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LIST OF TABLES
Table
Page
1.
Number of plants per 30 meter and early plant growth for two
cultivars of cowpea planted at four different dates
. . . . . . . . . . . , . 25
2.
Selected Pearson correlation coefficients among parameters
measured in the time of planting study . . . . . . . . . . . . . . . . . . . . . . 26
3.
Summary of weather data in 1990 (time of the planting study) . . . . . . . 27
4.
Total amount of water from rain and irrigation from planting to
15 days before harvest for each planting date . . . . . . . . . . . . . . . . . 28
5. Pod and seed parameters for two cultivars of cowpea planted at
four different dates . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . 30
6.
Mean length of pods of two cowpea cultivars from different
harvests for two planting dates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.
Seed and pod yields for two cultivars of cowpea planted at four
different dates
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . 34
8.
Size distribution (cumulative) of seeds produced by two cultivars
of cowpea planted at four different dates . . . . . . . ,, . . . . . . . . . . . . . :35
9.
Effects of seed size-density in two cowpea cultivars on the rate of
water absorption during imbibition and the critical moisture
content for germination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
10.
Leiigth and dry weight of the shoot, root and total seedling
produced from large-heavy and small-light seeds of two
cultivars of cowpea 8 days after planting
. . . . . . . . . . . . . . . . . . . . 38
11.
Field emergence, survival, rate of emergence, plant growth at 15
and 27 days, and number of branches and peduncles from large-
heavy and small-light seeds of two cultivars of cowpea
. . . . . . . . . . 40
12. Reproductive development, characteristics and yield of two
cultivars of cowpea . . . . . . . . . . . . . . . . . . . . . . . ,, . . . . . . . . . . . . . 42
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Table
Page
13. Length, number, and weight of pods per 3 meter row as affected
by seed size-density and cultivar . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
14. Selected Pearson correlation coefficients between some of the
parameters measured in the seed size-density study . . . . . . . . . . . . 45
15. Growth and development of two cultivars of cowpea in high and
low popuIation density . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . 47
16. Selected Pearson correlation coeffkients between some of the
parameters measured in the population density study
. . . . ., . . . . . 49
17. Reproductive development and characteristics of two cultivars of
cowpea in high and low population density . . . . . . . . . . . f . . . . . . . 50
18. Effects of population density, harvest time and cultivar on pod
length, and the number and weight of seeds per pod in cowpea . . . . 52
19. Number and weight of pods and number of plants per 3 meter row
for two cultivars of cowpea in high and low plant density . . . . . . . . 53
20. Size distribution (cumulative) of seeds of two cultivars of cowpea
produced in high and low density populations . . . . . . . . . . . r . . . . . 55
21. Size distribution (incremental) of seeds of two cultivars of cowpea
produced in high and low density populations . . . . ., . . . . . . . . . . . . 56
. . .
VI11

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CHAPTER 1
INTRODUCTION
Cowpea IVigna unguiculata CL.1 Walp.1, also called southern pea and
blackeye pea, had been cultivated for many centuries (51). It is one of the major
pulses in the sub-humid and humid tropics (41, and is widely grown in Africa,
India, Brazil and the Southern US.
Cowpea is cultivated for the edible seeds and forage. The growth habit
ranges from prostrate through semi-erect to erect or climbing. The pods are
variously coiled, round, crescent or linear in shape. Peduncles range from about
5 cm to 50 cm long (40). The seeds or grain exhibit a large diversity for “eye” (i.e.,
hilar area) patterns and colors, while the flowers and pods also vary widely in
pigmentation.
The number of days from sowing to pod maturity varies among
cultivai-s and land races from 53 days to 120 days when grown at Ibadan, Nigeria,
duikg the second growing season (40).
The suggestion that cowpea originated in Asia is not considered tenable in
view of the absence of progenitors there. The preponderance of evidence points to
its origin in Africa, although the site where the species was first domesticated is
unccrtai Il. Ethiopia, Central Africa, South Africa, and West Africa have a11 been
considcred as possible centers of domestication (40, 51).

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Cowpea is an important source of protein in the human diet wherever it is
grown, arid is especially important in the diet of children, pregnant and lactating
women t 7).
Food legumes, because of their high protein content, generally
constitute the natural protein supplement in staple diets. In Africa cowpea is the
legume of choice for millions of people. The chemical composition of cowpea seeds
is similar to that of other edible grain legumes:
about 24% proteins, 62%
carbohydrates, and small amounts of other nutrients. Most of the nutritive value
in cowpea, therefore, is provided by proteins and carbohydrates.
The most common method of preparing cowpeas is some form of “boiling,”
which, if not properly carried out, cari decrease their nutritional value (7).
Alternate modes of utilization include cowpea flour incorporated in wheat fleur to
make various forms of bread. Many novel fonds are also obtained from cowpea by
extrusion cooking which efficiently converts starchy and proteinaceous raw
materials into finished foods or intermediates that require only minimal further
proccssing. Commercial processors use extrusion cooking to produce cowpea-based
snack foods, ready-to-eat cereals, meat analogues, and pet foods (46).
Cowpea is primarily produced under rainfed conditions, but a portion is
procluced under irrigation in the Southern U.S. and Iraq. Cowpea is grown in
various “farming systems”: monoculture; mixed culture with millet, sorghum or
peanut; and relay cropping.
Cowpea is produced under an especially wide range of environmental factors
and cultural practices which cari affect seed yield and/or yield components and seed
yuality. Thc present studies were undertaken to develop additional information
ou thc cfkxAs of seked envinxunental and cultural practices on growth and development.
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The specifïc objectives of this study were:
1.
TO determine the effect of planting date on vegetative and
reproductive development, and relate patterns of development to
specifïc environmental factors.
2.
TO evaluate the influence of the size and density of the seeds planted
on growth and development.
3.
TO compare the patterns of growth and development of plants grown
in different population densities.

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CHARTER II
LITERATURE REVIEW
Effects of Seed Size and Density
Gregg (23) made one of the earliest and most compreh.ensive studies of the
association of density and physiological quality in seeds.
On the basis of
1)
exhaustive analyses, he demonstrated that the performance of cotton (:Gossypiur?z
hirsutwn L.) seeds, as manifested in germination and emergence, increased as
standard bulk density (pounds per bushel) of the seeds increased up to 46 lb/bu.
The increase in performance capability of the seeds with increasing density was
both consistent and uniform. Gregg’s fïndings have been corroborated by many
workers. Justus et al. (301 sized cotton seeds into three classes and graded each
class into f.ïve density groups. They reported that seeds of the same density from
the three size classes had similar germination responses, but that within a size
class, densi ty was much more highly correlated with field emergence than standard
germination percentage or vigor rating. In a later study, Phaneendranath (45)
separatcd cotton seeds into four specific gravity classes (~0.88, 0.88 - 0.93, 0.9:3 -
0.98, and 0.98-1.03). Laboratory germination and field emergence increased as
specific gravity of the seeds increased. Very recently (19881, Hofman et al. (26)
reported similar results: low density cotton seeds were signitïcantly inferior in a11
performance attributes measured to those of higher density.
4

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Unsrisong (56) reported that in soybean I Glycine j?zax (L.) Merrilll the low
density sceds had significantly lower germination than high density seeds. Payne
and Koszykowski (43), however, had pointed out earlier that there cari be a
confounding of seed size and density effects on soybean seed quality and seedling
growth.
Vaughan and Delouche (58) studied seed size, density and quality
relationships in three species of Trifolium. They first sized the seeds from several
lots of each species into small, medium and large size classes, and then separated
the seeds within each size class into low, intermediate and high density categories
with. a South Dakota seed blower. The medium and large size, high density seed.s
were highest in germination, while the small, low density seeds were poorest in
germination. While germination consistently increased as density of the seeds
increased, the relationship of seed quality and seed size varied among the species.
In one species, germination increased as seed size increased, w:hile in the other two
spccies, germination increased from the small to medium size class then decreased
from the medium to large size class.
Based on their review of the relevant literature up to the early 197Os,
Dhillar and Kler (13) concluded that there was an inconsistent relationship
betwcen seed size and seed quality. Yet, the superior performance capabilities of
largcr - as compared to smaller - seeds within a genotype have bcen reported by
Dharmalingan and Ramakrishivan (12) for peanut (Arachis hypogaea L. ), Jagadish
and, Shambulingappa (29) for sunflower Welianthus annus L.), Pearl millet
l Pmnisct iurn americanunl.
( L.) Leeke I (19) and other species ( 25, 28, 34, 45).

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Ficld Emer~~ence and Earlv Plant Growth
Many studies have established relationships between seed size and density
and field emergence and early plant growth. Unsrisong (56) found that the large
seeds of soybean were superior in emergence, and Oliveira (42) reported similar
fkdings for cowpea. Fontes and Ohlrogge (18), however, found that seed size has
no effect on the emergence of soybean. On the seed density side, Assman (1) found
that the heavier soybean seeds were more vigorous and emerged better than the
lighter seeds. The great influence of seed density on emergence, seedling and early
plant growth has been especially well documented for cotton (23, 26, 32). On the
other hand, the speed of emergence has been reported to be :inversely related to
seed size and/or density in soybean (2,28), mungbean [Vigna ~adiata (L.1 Wi1czek.I
(14), and in cowpea (42). Seedlings from the small seed size class emerged more
rapidly than did those from medium or large size classes.
This response is
generally attributed to the fact that the time required for seeds to attain the
critical moisture content for germination is directly related to the mass of seed
tissue that must be rehydrated (8, 40), and/or length of the diffusion path (13, 14).
In peanut, on the other hand, the large seeds exhibited the highest rate of
emergence speed ( 12). The early growth of seedlings appears to be influenced more
by the volume of cotyledons than by their weight. Seedling size is generally
positively correlated with seed size, but the cor-relation diminishes as the season,
ie., period of growth, increases (12, 15, 18, 32, 42). In the case of cowpea, the
largest secds produccd the highest number of “surviving” seedlings i42). Field
omcrgence, seedling and early plant growth have also been sbown to be positively
corrclatcd with thc sizc andlor density of the seeds planted in subterranean clover

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7
(TrifoZium subterranean L.), pearl millet (19), wheat (Rticu~~ aestiuum L.) (40),
sorghum I Sorghn bicolor (L.) Moench I (10,381, Pajzicunz antidotale Retz. (62 j and
Bengal gram (Citer arietinum L.) (57).
Hanumaiah and Andrews (25) studied seed size and performance
relationships in turnip (Brassica rapa L.) and cabbage (Brassica oleracea L.). They
found that scedling fresh weight and dry weight decreased as size of the seeds
plan ted decreased. In turnip, leaf development was significantly superior on plants
arising from large seeds as compared to those from small. seeds. Major (37)
obtained similar results with two rape species IBrassica campestris CL.>1 and 113.
napus L. (Koch)l.
Plant Growth and Yield
Dhillon and Kler (13) stated that the results of numerous studies on soybean
seeds showed that the heavier and/or larger seeds produced plants that were more
vigorous, taller, and more productive than those produced by smaller, lighter seeds.
The effects of inter-plant competition that arose when seeds of mixed sizes were
planted were great and the plants from the large and small seeds appeared to be
affected differently. The grain yields of plants from large seeds increased in
compctition, while those from small seeds decreased. On the other hand, Wood et
al. (61) revicwed the work with several species and concluded that the advantage
of large sceds diminishes as the season progresses and that crops from large and
small seeds eventually attain the same development and produce similar yields.
The more rapid growth of and higher yield from soybean plants from large
sccds as comparcd to those from small seeds was fïrst reported by Fontes and
Ohlroggc ( 183). They stated that the superior grain production of plants from large

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8
seeds was primarily the consequence of a higher number of pods per plant as the
number of seeds per pod was not affected by seed size. Hoy and Gambie (28) found
that seed size had little effect on yield in early and late plantings of soybean, but
plantings of high density seeds outyielded those from low density seeds in late
plantings. The lowest density seeds within broad size classes of cotton seeds
produced crops that were consistently and signifïcantly lower in Iint yield than
those from high density seeds (26). The yield differences, however, were not great.,
and the authors concluded that when stands were adequate, the effects of seed
density were minimal. In the case of peanuts, Dharmalingan and Ramakrishnan
( 12) found that the number of primary branches, the pod yie1.d and the lOO-seeds
weight increased as the size of seeds planted increased. Oliveira (421, working with
cowpea, found that seed size affected the 100~seeds weight but not total yield or the
components of yield. Similarly, seed size in broadbean (Vicia faba L.) had no
consistent effects on the components of yield or total yield (49).
Somewhat different findings have been reported in the case of the small
seeded leguminous forage crops. Black (6j, working with subterraneum clover
concluded that shoot weight, leaf area, and over-a11 vegetative growth were greatly
influenccd by the weight, or, more fundamentally, the initial cotyledonary vo1um.e
of the seeds planted. Williams et al. (60) confnmed Black’s fïndings and extended
thern to crimson clover (Trifolium incarnatunt L.). The leaf area index (ratio of leaf
area to ground area) at 73 days for the communities developed from large seeds
cxceedcd that of the communities from small seeds by more tban one unit. A 35%
increase in leaf area was associated with a doubling of the size of seeds planted.

---

The topmost leaves of the communities from large seeds were also much higher
than those from the small seeds.
Working with Pearl millet, Lawan et al. (34) found that seedling height at
24 days was positively correlated with seed density. Furthermore, the number of
days from seeding to anthesis decreased from 70 for plants from small-low densit:y
seeds to 62 for plants from high density seeds. Low density seeds also produced
the lowest number of heads, lowest head weight and lowest yield per hectare.
Similar results were reported by Garner and Vanderlip (19) for Pearl millet, but
Maranville and Clegg (38) and Choudari et al. (10) did not find any differences in
sorghum grain yield due to the size or density of the seeds planted. Several other
workers reported that seed size-density affected early vegetative growth but not
yield (25, 38, 52).
Othor Aspects of Seed Q.uality
Differences in performance of seedlings from large and/or heavy seeds as
compared to small and/or light seeds appear to be the result of differences in
chemical composition and biochemical activity.
Gaybe et al. (21), working with 22 cultivars of cotton in India, found that
seed density (mass per unit volume) was a better indicator of seed quality than
sced index (gr/lOO seeds) when quantified in terms of lipid and nitrogen content.
The quantity of both organic and inorganic material available to the developing
seedling increased with seed density. Similar findings were reported by Krieg and
Bartee (32). They noted that as the density of cotton seeds increased, the increase
in lipids was grcater than the increase in nitrogen and carbohydratcs. Since the
lipid fraction provides the highest energy per unit weight, it was expected that high
--._-
-.
--s--s
-1

---

10
density sceds would exhibit superior vigor. The high density aeeds also contained
more fret sugars and adenylate phosphates for further phosphorylation. Earlier,
Phaneendranath (45) found that free fat acidity in cotton seeds decreased as seed
density increased.
Vaughan and Delouche (SS), working with red clover (Z’rifoliunzpr-atelzse
L.11,
white clover (Trifoliunz repens L.) and crimson clover, found that hardseededness
was associated with seed size and density. The highest percentage of hard seeds
was found in small-heavy seed class.
McDaniel (39) reported that seedling fresh weight, seedling mitochondrial
protein and mitochondrial biochemical activity in barley (Hordeum uulgure L.) were
correlated with seed weight. The high quantity of mitochondrial protein in
seedlings from heavy seeds was associated with a high respiratory rate and high
level of ttnergy (ATP) production. Seedlings from heavy seeds, therefore, had a
greater growth potential than those from light seeds.
Effects of Plant Population Density
Plant population density has profound effects on plant growth and
dcvolopment in many species. In their extensive study of plant population effects
in soybean, Hoggard et al. (27) observed that the number of pods per plants
decreased as plant density increased.
The length of the lower and central
internodes and internode number also declined as population increased in two of
the three cultivars studied. The highest yield was obtained from the 240,060
Plant&a population. The negative effects of shade on growth and yield in soybean
were cxplained by Egli (16) in terms of interplant competition. Overall, plant
growth decreased as shading and population increased. Leaf starch and soluble

---

1 1
sugars were reduced by the shade, but increased as the population density
decreased. The distribution of dry matter between vegetative and reproductive
plant parts was relatively constant across large differences in plant size and growth
rate, and it appeared that fruit and seed numbers were more closely related to
growth rate than to the partitioning of assimilate.
Rmtes and Ohlrogge (18) observed that yield in soybean decreased as th.e
plant population increased, and the number of barren plants increased. The barren
plants utilized water and nutrients but contributed nothing to yield. Copper (11)
pointed out that indeterminacy in soybean genotypes was an important factor in
determining lodging and yield response to seeding rate. Seed yields were generalliy
unaffected by seeding rate when there were no differences in lodging.
Grafton et aZ. (22) concluded that indeterminate types of beans U’haseolus
uu.lgaria L. 1 had a greater capacity for yield compensation across wide differences
in population than determinate types. Similar results were reported earlier by
Westermann et al. (59). They contended that seed yieldkrrea in bean is relatively
constant over a wide range of plant populations for the indeterminate cultivars, but
decrcases as plant population decreases for the determinate cultivars. Based on
the results of his class study, Adams (1) stated that in the navy bean, the
components of yield are, in order of their development, the number of pods per
plant or per unit area, the mean number of seeds per pod, and the mean seed size.
Environmentally induced differences among yield components occur when there is
competition for limited nutrients or photosynthates. A reduction or increase in one
yield component cari be compensated by an increase or decrease in another yield
component. Such a “buffered” system results in a substantial yield stability due

---

1 2
to the developmental plasticity of the yield components, and, theoretically, limit the
potential yield gains through increases in population. Wood et al. (61) agreed with
Adam’s analysis.
Negative correlation between yield components (racemes per node and nodes
per branch) and population density in bean was demonstrated by Bennett el al. (5:~.
They stated that plant density constituted a special kind of stress which had its
greatest effect at the time of maximum leaf area which coincided with the earl~y
reproductive phase. Longden (34) pointed out that the plant variation in pea
(Pisunz saGvunt L.) accounted for 85% of the variation in seed yield, while the
bctween node variation accounted for ll%, and the within node variation for only
4%.
Environmental Effects
The growth, development, and reproduction in plants are profoundly af’fected
by the environment in which the plants are grown. Kittock and Williams (37~3
studied the effect of planting time on the growth and yield of castorbean (Ricin~s
commutais L.) in Nebraska. They found that for non-irrigated culture, there was
little differcnce in yield among any plantings made in May, but the yield was
reduced for the April and June plantings. Seeds from the tertiary and quaternary
racemes decreased drastically in weight for plantings later than May.
Summerfield et nl. t 53) reported that cowpea leaves are initiated about twice
as rapidly at XY’C as at 20°C. The minimal temperature for leaf appearance and
expression was estimated at 16°C. It appeared that the onset and rate of leaf
scnesccncc: was hastened by hot, arid conditions, but the effects of environment at
this stage were difficult to separate from those associated with reproductive load

---

1:3
and the synchrony of seed Iïlling.
It is likely that both hormonal and nutritional
factors wore involved. Detrimental effects of heat on cowpea production have been
demonstrated by Hall and Patel (24). High night temperature was much more
damaging than high day temperature. In growth chamber and fïeld studies, it was
determined that temperatures that commonly occur at night in the tropics caused
male sterility and substantially reduced grain yield as a consequence of floral and
pod abscission.
High day temperature resulted in seeds with asymmetric
cotyledons. Plants avoided drought by a reduction in leaf area, a decrease in
stomatal conductance, and changes in leaflet orientation.
Reproductive development, yield potential and seed yield in cowpeas are
notoriously sensitive to the vagaries of weather. Studies have shown that some
cowpea gcnotypcs respond to photoperiod in a manner typical of quantitative short
day plants, while other genotypes are insensitive to a wide range of photoperiodls
(53). In addition to temperature, photoperiod and drought, solar radiation is of
importance in plant development. Burton et al. (9) studied the relationship amon.g
climatic parameters and forage yield for irrigated and rain-fed costal bermudagrass
( QlldOSZ dactyh L. 1. Based on stepwise multiple regression of yields from
individual cuttings on the various climatic parameters, they found that day length
was the single most important variable affecting yield (r = 0.64). Over many years,
yicld was most highly correlated with day length and solar radiation (r = 0.95 and
0.93,
reiipectively).
Rocheford et al. (48) conducted a two-year study to assess the effects of early
and latc plantings on growth and development in soft red winter wheat. The yield
component most affected by planting date was the number of heads (spikes) per

---

1 4
unit area. Mahalakshmi et ai. (35) demonstrated that changes in water status
during plant growth were most detrimental to yield in pearl millet when they
generated a “stress” at a critical phase of plant development. Seed number and
size were reduced in proportion to the intensity of water deficit. Grain yield and
grain number, but not grain size, were affected by the time of onset of the stress.
The intensity and timing of the moisture stress accounted for 75% of the variation
in measured grain yield.

---

CHAPTER III
MATERIALS AND METHODS
Time of Planting Experiment
Two cultivars of cowpea, Mississippi Pinkeye (MS PE) and Mississippi
Bunch Purplehull (MS BP), were utilized in this study. The seeds were produced
in 1989 on the Plant Science Research Center, Mississippi Agriculture and Forestr,y
Experimen t Station (MAFES), Mississippi State, MS, hand harvested and threshed
and cleaned with a air-screen cleaner. After processing, the seeds were stored at
5°C and 50% relative humidity (RH).
For this experiment seeds were planted on four different dates: May 30,
June 21, July 12 and August 4 in 1990. Two 30 m rows per cultivar were seeded
with 600 seeds per row. The design was a completely randomized design with two
replications.
Methods and Measurements
seedling Dry Weight. Ten seedlings per replication were randomly selected
from each cultivar and planting date at 25 and 35 days after sowing for
determination of seedling dry weight. The seedlings were harvested by cutting
them wiih a razor blade at the soi1 level and dried at 80°C for 24 to 48 hr to obtain
the dry weight. The dry weight was calculated and expressed as the mean dry
weight per seedling.
1 5

---

1 6
Number of Flowers. At the beginning of flowering, fîve plants from each
c
replication were randomly selected for determination of the number of fiowers
produced. The number of flowers was counted every 2 or 4 days until the fïrst
harvest. The data obtained were used to calculate the mean number of flowers per
plant.
gods and Seeds. Pods were harvested only after they had begun to dry. Th.e
number of plants harvested was recorded as well as the number of pods. A LO-pod
sample was taken at each harvest for determination of seed moisture content. Tbe
seed moi.sture content was determined by drying the seeds at 105°C for 24 hr and
expressed on a wet weight basis.
The harvest times were 76,82 and 96 days for the fïrst planting, 76 and 82
days for the second planting, 76 days for the third planting, and 96 days for the
fourth planting. Pod length was determined by direct measurement of 50 pods
taken at. random per replication at each harvest. The harvested pods were allowed
to dry thoroughly under ambient conditions before they was weighed and hand
threshed to obtain the seed yield.
Secd Size Distribution. About 1 kg of seeds per replication were used for
determination of the seed size distribution. The seeds were sieved through a series
of sieve:s that decreased in size (diameter) of opening by 1/64 inch: 18/64, 17/64,
16/64, 15/64 and 14/64 inch. The percentage of seeds by weight within each size
category was determined, i.e., >18/64, 17/64-18/64, 16164-17164, 15164-16164, 14/64-
15/64, <:14/64 inch.
Jlil
,../ mum...-,--..

..- -..

“.----
-
m----1.

---

17
Weather Data
Pertinent weather measurements were obtained from the USDA weather
station on the MAFES Plant Science Farm. The measurements were used to
calculate the following data:
-
Total rainfall (from planting to harvest) for each planting date
- Mean daily rainfall
-
Sum of the mean daily temperatures from planting to harvest; for each
planting date
- Mean daily rainfall
-
Sum of maximum daily temperatures from planting to harvest
-
Sum of minimum daily temperatures from planting to harvest
-
Mean daily solar radiation in Kw/M2.
Seed Size and Density Experiment
Seed Materials
The MS Pinkeye and Bunch Purplehull cultivars were used in this studiy.
The seeds were produced in 1990 on the MAFES Plant Science Fat-m, hand
harvested and threshed, cleaned and stored at 5°C and 50% relative humidity (RI-I)
until needed for the study. Several kg of seeds of each cultivar were sieved with
hand screens with 18/64 and 15/64 inch round perforations to obtain sublots of
large and small size seeds. The large seeds were greater than 18/64 inch in
diameter, while the small seeds were less than 15/64 inch in diameter (but not
including shrivelled seeds).
The largest seeds (>18/64 inch) and small seeds (<15/64 inch) ‘were
sepuralcd into light and heavy fractions with a Stults seed blower set at 15, Psi.

---

18
For each cultivar, therefore, four sublots of seeds were obtained: large/heavy;
large/light; small/heavy; and small/light. It was decided to use only the extremes
for the study, i.e., large/heavy and small/light seeds. The lOO-seeds weights for the
two size/weight seed classes were:
Cul tivar
Large-heavv
Small-light
__--_-__---___-__-_-__
gr m__--m----m----m---m
MS Pinkeye
20.27
9.38
MS Bunch Purplehull
19.21
8.75
Field Planting
Seeds from the large-heavy and small-light categories were planted Sune 14,
1991 on the MAFES Plant Science FZesearch Center. The experimental design was
a two-way completely randomized design with four treatments (MS Pinkeye - large-
heavy and small-light seeds, and MS Bunch Purplehull - large-heavy and small-
light seeds) and five replications per treatment. Each replication or plot consisted
of a 2 m row with 0.5 m spacing between rows. One hundred seeds were hand
planted per 3 m plot at a planting depth of approximately 4 cm. The seeds were
treated with Captain WP50 dust before planting.
The observations and measurements made in each plot throughout the
growing season are descrihed below.
Rate and Percent Emergence
Emergence was counted daily through 16 days after planting. A seedling
was considcred emerged when the hypocotyl “crook” had completely straightened
and thc C(JtyhhllS were clear of the soil. The daily increments of emergence were

---

1 9
used to calculate a speed of emergence index using the formula developed by
Maguire t 36 1. The daily increments of emergence through 16 days were summed
and calculated as the percent emergence. On the 17th day after planting each plot
was thinned to 60 plants. The population was further reduced to 40 plants,/plot by
27 days after planting.
Dry Weirrht
At 19 and 27 days after planting 10 plants were randomly selected in each
plot and tut at the ground level. The plants were dried for 48 hr in a forage drier
to obtain the dry weight per seedhng or plant.
Seedling Survival
Seedling survival was determined for each plot by dividing the total number
of plants surviving 17 days after planting by 100, the number of seeds planted, and
expressing the results as a percentage.
Yicld Comnonents and Yield
F’orty-six days after planting the number of branches and floral peduncles
werc counted on fïve plants randomly selected in each plot. After physiological
maturity when many of the pods started to dry, a11 “harvestable pods” from each
plot were hand picked, counted and natural-air dried for several days. From the
harvcst of each plot, a sample of 50 pods was randomly taken for determination of
pod length, number of seeds per pod, and weight of seeds per pod. These ‘were
rcturncd to the total harvest for each plot for the plot or bulk determinations. The
total pods harvested from each plot were weighed, hand threshed and cleaned and
used for othcr measurements.

---

20
Wei~ht of 100 Seeds
A sample of 90 g of seeds was obtained from the total harvest for each plot
with a Boerner divider. Four replications of 100 seeds were then weighed and the
mcan 100 seeds weight calculated and adjusted for 13% moisture content.
Weight of Pods Per Plant
The total weight of pods from each plot was divided by the number of plants
harvested to obtain the weight of pods per plant.
Weight of Seeds Per Plot
The mean seed weight per plot was determined in a manner similar to that
described for pod weight per plant.
Yield
The mean seed weight in kg produced on each plot was converted to kg/ha
by multiplying the plot (1.5 m”) yield by the appropriate factor.
Rate of Imbibition
Four replications of 50 seeds from the “original” large-heavy and small-light
categories for the two cuitivars were used to determine the rate of imbibition. The
initial moisture content of the seeds was fïrst determined (24 hr at 105°C in forced
air aven). Then, the 50-seed replicates were weighed and placed between three
moist germination towels in a germinator at 20-30°C. The seeds were weighed each
hour until the time at which 50% of the seeds exhibited radicle protrusion to obtain
data for calculation of the rate of imbibition. At the 50% radicle protrusion stage,
the seeds were removed from the media for determination of the moisture content

---

21
which was taken as the critical level of hydration (or moisture content) for
germination.
SeedlinP Growth Rate
Ten seeds for each cultivar-treatment combination were planted on moist
germination blotters in a straight line approximately 5 to 7.5 cm from one edge
with the radicle end of each seed oriented in the same direction, and covered with
a second moist blotter. The germinator trays with the tests were positioned in a
20-30°C germinator at a 45” angle with radicle ends pointed downward. Eight days
after planting, the seedlings were separated into radicles and shoots (hypocotyl and
above) and dried in a forage drier to obtain the dry weight which were expressed
as the dry weight per seedling component.
The experimental design was a
completely randomized design with six replications.
Plant Population Density Study
Seeds of the MS Pinkeye and MS Bunch Purplehull cultivars produced
during 1990 on the MAFES Plant Science Fat-m were used. The seeds were hand
threshed, clean and stored at 5°C and 50% RH until planting time. Prior to
planting, the seeds were sized to obtain uniform populations of seeds between 17/64
and 16/64 inch in diameter. Thirty seeds for the low population and 120 seeds for
the high population treatments were planted June 14, 1991 on the MAFES Pla.nt
Science Farm in 3 m rows 0.5 m apart. The design was a completely randomized
design with five replications.
Twenty-three days after planting the plots (rows) were thinned to 25 plants
for the low population and 70 plants for the high population.

---

22
Field Emergence and Survival
Rate of emergence in percentage based on the number of seeds planted was
determined through 16 days after planting. The number of dead or dying plants
was also recorded daily to determine the survival percentage.
Seedling Dry Weight
Nineteen and 27 days after planting, fïve plants per replication were
randomly selected and tut at ground level for dry weight determinations following
procedures previously described. The populations after the 27”day seedling harvest
were 15 plants per row for the low population and 60 plants per row for the high
population.
Plant Height
Five plants randomly selected were measured from the soi1 line to the tip
of the longest branch 32 days after planting.
Flowerillg
The dates ofappearance of the first flower and the 50% flowering stage were
recorded.
Yield and Yield Components
The number of branches and floral peduncles were counted for each of five
plants randomly selected 47 days after planting. Pods were harvested (after
physiological maturity) 67, 73 and 80 days after planting and allowed to air dry.
IJifty pods wcre randomly taken for determination of pod length, number of seeds
pcr pod and wcight of seeds per pod. Other measurcmcnts were made using

---

2 3
procedurcs previously described. These included: 100-seeds weight; weight of pods
per plant; weight of seeds per plant; and yield per hectare adjusted for 13%
moisture content.
Number of Plants Per Unit Area
For each plot, the number of plants that survived until the harvest was
divided by 1.5 m2 (3 m row x 0.5 m spacing) to establish the number of plants per
unit area. The number of plants per meter of row was also calculated.
Secd Size Distribution
The seed size distribution of the harvested seeds was det’ermined by
procedures previously described.
Statistical Analyses
Analyses of variante were made of the measurement data from each of the
three studies.
When appropriate, the means were separated and tested for
significant differences using the LSD method.

---

CHAPTER IV
RESULTS AND DISCUSSION
Effects of Planting Date on Growth and Development
Seedling Growth
Although only a partial statistical analysis was carried out on seed.ling
growth due to the limited number of observations (six), the data in Table 1 show
a consistent decrease in seedling dry weight with lateness of planting.
The
differences in seedling or plant dry weight among planting times were most
pronounced 35 days after planting. Seedling dry weight was positively correlated
(r = 0.480) with the sum of maximum daily temperatures (Tables 2,3 and 4). The
higher maximum daily temperatures associated with earliness of planting
undoubtedly contributed to the increase in seedling dry weight but did not account
for a11 the variation observed among planting dates. The average daily rainfall and
thc sum of the mean daily temperatures seemed also to be involved through their
interaction with planting date. The sum of the mean daily temperatures was
higher for the May and June planting dates than for the July and August planting
dates. Cowpea leaves were initiated about twice as rapidly at 30°C as at 20°C (53).
Low night temperatures were associated with the August planting date.
2 4

---

2 5
Table 1 . Number of plants per 30 meter and early plant growth for two cultivars
of cowpea planted at four different dates.
Parameter/
Plan ting Date
MS Pinkeye
MS Bunch Purplehull
Plants/30 m
______.._____m_
No e_________-____
May 30
1 3 0
1 2 5
Jun 21
3 8 5
3 9 5
Jul 12
4 3 8
426
Aug 4
4 3 8
426
25Day Dry Wgt
___________----
gr ---------------
Jun 21
2.7
2.5
Jul 12
1.0
1.1
Aug 4
0.8
1.2
35-Day Dry Wgt
_______________ gr --_--_-- --_-
Jun 21
5.1
4.6
tJul 12
2.2
2.9
Aug 4
1.9
2.3

---

Table 2. Selected Pearson cor-relation coefficients among parameters measured in the time of planting study.
* Signifïcant at the 0.05 probability level
** Significant at the 0 01 probability level
Code: SDW = Seedling dry weight
SWP = Seed weight per plant
SRD = Sum of solar radiation
NFL = Number of flowers per plant
WSR = Weight of seed per row
ARD = Average daily radiation
NPP = Number of pods per plant
WPR = Weight of pods per 30 ft row
SMIT = Sum of minimum temperature
PWP = Pod weight per plant
PL
= Pod length
SMAT = Sum of maximum temperature
SATARD = Interaction between sum of average temperatures and average solar radiation
SATADR = Interaction between sum of average daily temperature and average daily rain.
SATSDR = Interaction between sum of average temperature and sum of solar radiation
SMATTR = Interaction between sum of maximum daily temperature and total rain.

---

27
Table 3. Summary of weather data in 1990 (time of the planting study).
Month
Climatic Data
Max.
Min.
Avg.
AviS
Temp. (“F)
Temp. (“F)
Temp. (“F)
C Temp. (OF)
Jun
89.5
67.1
77.7
2,332
Jul
89.3
69.4
78.2
2,426
Aug
92.6
69.1
79.8
2,475
Sep
90.1
64.4
75.8
2,275
o c t
75.1
46.7
60.3
1,870
Jun
4
7.4
6.8
Jul
6.3
7.5
6.3
Aug
1.5
7.5
6.3
Sep
1.3
6.2
5.2
C Max. Temp.’
1 Min. Temp.’
X Solar Rad. ’
““““““““““““““““““““““““F ““““““““““““““““““““““”
---KW/MSQ---
Mw
2774
2067
583.2
June
2870
2123
515.7
Jul
2742
2011
451.7
Aug
2233
1343
414.5
’ C of the maximum and minimum temperatures and solar radiation for the entire
growing period of the Plantings made in the indicated months.

---

28
Tablc 4 . Total amount of water from rain and irrigation from planting to 15 days
before harvest for each planting date.
Planting
Date
MS Pinkeye
MS Bunch Purplehull
-----------------mm--------------
May 30
278
278
Jun 21
210
210
Jul 12
125
125
Aug 4
93
93

---

2 9
Numbcr of Flowcrs Per Plant
The number of flowers produced per plant decreased from the eJune planting
to the August planting (Table 5). The May and June plantings produced about the
same number of flowers/plants, while the July and August plantings produced less
than half as many flowers. High maximum temperatures before and during
flowering and relatively low soi1 moisture contents might have contributed to the
reduced number of flowers for the July planting. In the case of the August
planting, drought, cool night temperatures and low solar radiation (Table 3) might
have been contributing factors. The number of flowers per plant was signifïcantly
correlated with the interaction of sum of mean temperatures x mean daily radiation
(r = 0.916), and the interaction between the sum of the maximum daily
temperatures x total rain (r = 0.891) (Table 2).
Plants avoid drought by a reduction in leaf area, decrease in stomatal
conductance, and changes in leaflet orientation (24). The August and July
plantings for both cultivars had manifestly less vegetative development as
compared to the earlier plantings. The decrease in photosynthetic area associated
wi th the decrease in vegetative mass probably resulted in a lower quali ty of flowers
produced. Moreover, flower abortion was observed for the June planting (four
consecutive days with maximum of 99°F or more during flowering) and the July
plant& (9 days with maximum of 99°F or more were recorded).
High
temperatures were reported by Hall and Patel (24) to cause male sterility and to
substantially reduce grain yield by increasing floral abscission and decreasing the
number of pods/m”. The number of flowers per pIant was signifïcantly correlated
(r = 0.883) with the number of pods per plant (Table 2).

---

30
Table 5.
Pod and seed parameters for two cultivars of cowpea planted at four
different dates.
Paramet&
Planting Date
MS Pinkeye
MS Bunch Purplehull
Flowers/Plant
_______________No
h_______----_--
-
May 30
17 A
11 A
Jun 21
17 A
10 A
Jul 12
5 B
4 B
Aug 4
2 B
2 B
Pods/Plant
..______________ No .__________-____--
May 30
12.3A
9.9A
Jun 21
6.7B
4.1B
Jul 12
1.6C
1x
Aug 4
O.lC
0.2c
Pods/Plant
““““““““““““““““gr
““““““““““““““““”
May 30
32.2A
20.4A
Jun 21
12.5B
8.8B
Jul 12
2.7C
2.oc
Aug 4
O.lC
0.2c
Pod Length
May 30
16.8A
14.8A
Jun 21
17.2A
14.2A
Jul 12
15.2A
13.2A
Aug 4
10.2A
11.2A
Secds/Plant
““““““““““““““““” gr “““““““““” I”“” “““”
May 30
23.25A
14.60A
Jun 21
9.90B
5.90B
Jul 12
2.00B
1.40B
Aug 4
0.09B
0.18B
I’arameter means in columns not followed by the same capital letter differ
significantly at the 5% level of probability according to LSD.

---

31
Pod and Seed Number and Weight Per Plant
The number of pods per plant decreased as planting date was delayed (Table
5). The May and June plantings produced significantly more pods per plant than
did the July and August plantings. The several factors discussed above as
contributing,to the reduction in number of flowers/plant with lateness of planting
were undoubtedly also involved in the reduction of the number of pods/plant.
The
number of pods/plant was correlated with the sum of solar radiation from planting
to 30 days before harvest (r = 0.969) (Table 2). The number of pods/plant was also
signifïcantly correlated with the interaction between the sum of the mean
temperatures and average daily rainfall (r = 0.965), and the interaction between
the sum of the mean daily temperatures and the sum of solar radiation (r = 0.946).
Similar correlations were recorded by Burton et al. (9) for coastal bermudagrass:
over many years, forage yield was most highly correlated with day length and solar
radiation.
A.s expected, the number of pods/plant was highly correlated with seed and
pod weight per plant, and the weight of pods and seeds per row (Table 2). The
number of pods/plant was the major factor involved in the yield differences among
planting dates.
The trends in pod and seed weight per plant were similar to that of the
number of pods/plant. Pod weight/plant was signikantly correlated with pod
numbcr/plant (r = 0.989) but not with pod length (Table 2).
Sceds yield per plant decreased with lateness of the planting date and was
significantly correlated with pod weight per plant (r = 0.998), the number of pods

---

---

33
Table 6.
Mean length of pods of two cowpea cultivars from different harvests for
two planting dates.
Parameterl
Harvest
MS Pinkeye
MS Bunch Purplehull
-------May 30 Planting------
Pod Length (cm)
First Harvest
17.2
15.0
Second Harvest
16.0
12.5
Third Harvest
14.8
11.8
Pod LenPth (cm)
-------June 21 Planting-----
First Harvest
18.0
14.5
Second Harvest
15.2
12.8

---

34
Table 7. Seed and pod yields for two cultivars of cowpea planted at four different
dates.
Parameterl
Planting Date
MS Pinkeye
MS Bunch Purplehull
-
---______-------- p -----------------
Pod Yield/30 m Row
May 30
4183A
2554A
Jun 21
4802A
3460A
Jul 12
1175B
857B
Aug 4
54c
103c
Seed Yield&O m Row
May 30
3022A
18238
Jun 21
3826A
2319A
Jul 12
859B
605B
Aug 4
37c
76C
lOO-Seeds Wgt.
May 30
18.95A
16.45A
Jun 21
17.30A
14.51A
Jul 12
18.10A
13.10A
Aug 4
15.3412
14.55A
Parameter mcans in columns not followed by the same capital letter ,differ
significantly at the 5% level of probability according to LSD.

---

3 5
Table 8. Size distribution (cumulative) of seeds produced by two cultivars of
cowpea planted at four different dates.
Seed Size/
Planting Date
MS Pinkeye
MS Bunch Purplehull
> 18/64 Inch
May 30
23.7
13.5
Jun 21
8.4
4.2
Jul 12
25.9
2.2
> 17/64 Inch
May 30
63.0
37.9
Jun 21
40.1
27.0
Jul 12
59.2
12.3
> 16/64 lnch
May 30
89.8
75.8
Jun 21
71.6
65.2
Jul 12
83.8
40.6
> 1.5/64 Inch
May 30
97.0
92.3
Jun 24
91.3
87.5
Jul 12
94.2
67.2

---

3 6
General Observation
The effects of planting date on growth and development of cowpea were
primarily environmental. Major environmental factors such as temperature (mean,
maximum, night), solar radiation, and water supply varied substantially among the
planting dates.
The efYects of some of these factors on specific parameters of
growth and development were considered above.
Seed Size-Densitv Effects
Germination
The data in Table 9 show that in the laboratory, large-heavy seeds required
27 hr for radicle protrusion in both cultivars, whereas, small-light seeds required
only 20 and 22 hr for “germination.”
Small-light seeds, however, had a
significantly higher critical moisture content for germination than did large-heavy
seeds for both cultivars. This cari be attributed to the greater amount of water
absorbed per unit weight (0.94 vs 0.85 gr/gr) for germination of the small-light
seeds as compared to the large-heavy seeds. The large-heavy seeds also exhibited
a higher rate of water absorption than the small-light seeds for bath cultivars.
While the large-heavy seeds absorbed water at the highest rate (larger contact
surface) they took more time to germinate than did small-light seeds. They not
only required more water to germinate, but also more time for seed coat saturation
and moisture migration to the tenter of the embryo, i.e. longer diffusion path (9).
Secdling Growth
In the laboratory, 8-day old seedlings from large-heavy seeds were
significantly longer than those from small-light seeds (Table 10). The difference

---

3 7
Table 9. Affects of seed size-density in two cowpea cultivars on the rate of water
absorption during imbibition and the critical moisture content for
germination.
Seed
Size-Density
MS Pinkeye
MS Bunch Purplehull
-----Initial Moisture Content (%o)------
Large-heavy
9.11
11.33
Small-light
9.28
9.22
--------Critical Moisture Content (%)--------
Large-heavy
53.37 Aa
53.49 Aa
Small-light
58.29 Ba
56.82 Ba
____________T&e Required (hr) -__---___
Large-heavy
27.00
27.00
Small-light
20.00
22.00
--Rate of Water Absorption (gr/hr)--
Largeheavy
0.34
0.34
Small-light
0.20
0.21
---Weight of Water Absorbed (gr/seed)-----
Large-heavy
9.24 Aa
9.01 Aa
Small-light
3.91 Ba
4.74 Ba
Parameter means in columns not followed by the same capital letter and in rows
not followed by the same lower case letter differ significantly at the 5% level of
probabili ty according to LSD.

---

38
Table 10. Length and dry weight of the shoot, root and total seedling produced
from large-heavy and small-light seeds of two cultivars of cowpea 8
days after planting.
Parameter/
Seed Size-Density
MS Pinkeye
MS Bunch Purplehull
Shoot Length
---------------------cm---------------------
Large-hcavy
20.0 Aa
25.0 Ab
Small-light
22.0 Aa
24.6 Ab
Root Length
Large-heavy
27.2 Aa
26.6 Aa
Small-light
23.8 Ba
23.1 Ba
&edlinP Lentih
Large-heavy
47.2 Aa
51.7 Ab
Small-light
45.8 Ba
47.8 Bb
Shoot Dry Weight
______________________ gr _______________-_ _____
Large-heavy
0.09 Aa
0.09 Aa
Small-light
0.04 Ba
0.04 Ba
Root Drv Weight
Large-heavy
0.02 Aa
0.02 Aa
Small-light
0.02 Aa
0.01 Aa
Seedling Dry Weight
L,arge-hcavy
0.10 Aa
0.11 Aa
Small-light
0.06 Ba
0.06 Ba
-
i
E’arameter means in columns not followed by the same capital letter and in rows
not followed by the same lower case letter differ signifïcantly at the 5% level of
probability according to LSD.

---

39
was mainly in the length of the root or radicle. On the other hand, seedling shoot
and total dry weight differed signifïcantly between the large-heavy and small-hght
seed classes mainly due to the heavier shoot produced by the large-heavy seeds.
The apparent contradiction between the seedling length parameter where
the root was responsible for the greater length of seedlings from large-heavy seeds
and the seedling weight parameter where the difference between seedlings from
large-heavy and small seeds was due to the shoot, cari be explained by the thicker
and heavier shoots produced by the large-heavy seeds. The superior vigor of heavy
seeds has been shown to be positively associated with higher respiratory rate and
greater energy (ATP) production in barley (38), and higher lipid and nitrogen
content in cotton (22, 31).
Emergence and Survival
The percent field emergence and speed of emergence were signifïcantly
affected by seed size-density (Table 11). The large-heavy seeds emerged more
slowly but to the highest percentage. Similar results were obtained by other
researchers for cotton (23, 39), sorghum (371, and Pearl millet (20, 32). The higher
rate of emergence of small seeds as compared to large seeds has been reported by
Dillon cl al. (15) in mungbeans, Oliveira (42) in cowpea, Dhillon and Kler (14) in
triticale, and others in Pearl millet and sorghum (20, 37).
The large-heavy seeds not only emerged to a higher percentage than. the
small-light seeds, the percentage of the plants that survived the seedling stage was
also higher. Similar results were reported in cowpea (42), and Bengal gram (581.

---

40
Table 11. Field emergence, survival, rate of emergence, plant growth at 15 and 27
days, and number of branches and peduncles from large-heavy and
small-light seeds of two cultivars of cowpea.
Paramcter/
Seed Size-Densi ty
MS Pinkeye
MS Bunch Purplehull
Emergence
Large-heavy
82.00 Aa
87.00 Aa
Small-light
76.40 Ba
71.40 Ba
Survival
Large-heavy
91.98 Aa
89.39 Aa
Small-light
80.53 Ba
76.65 Ba
Rate of Emerg.
_______________________Index _______-_-_~_ _ ____
Large-heavy
13.81 Aa
15.42 Aa
Small-light
16.26 Ba
15.80 Ba
15Day Dry Weight
_______-___-_---___--- gr__-_--_-_----__-------
Large-heavy
0.56 Aa
0.12 Aa
Small-light
0.35 Ba
0.06 Ba
27-Day Dry Weight
Large-heavy
3.19 Aa
3.54 Aa
Small-light
2.43 Ba
2.28 Ba
~ranches/Plant
______________________No .___-____________-------
Large-heavy
2.6 Aa
1.0 Ab
Small-light
2.2 Aa
0.8 Ab
Peduncles/Plant
Large-heavy
9.0 Aa
6.4 Aa
Small-light
6.6 Aa
7.0 Aa
Paramctcr means in columns not followed by the same capital letter and in rows
net followed by the same lower case letter differ significantly at the 5% level of
probability according to LSD.
-. .- - ,_-- ---
n*---
II*

---

4 1
&edling and Plant Growth
The 15 and 27 day seedling weights were signifïcantly higher for the large-
heavy seeds than the small-light seeds (Table 11). These fïndings are in agreement
with those reported by others for a variety of species (7, 11, 13, 26,31, 50,58, 62).
In epigeal seeds, larger seedling size is usually the result of greater cotyledonary
area and photosynthetic activity immediately after emergence (55). The doubling
of ,seed size in crimson clover and subterranean clover produced a 35% increase in
Ieaf area (61).
The numbers of branches and floral peduncles per plant were not
significantly affected by the size-density of the seeds planted.
Reproductive Development
Plants from large-heavy seeds produced their first flower 2 to 3 days earlier
than plants from small-light seeds despite the fact that the small-light seeds
emerged somewhat earlier (Table 12). Similar results have been reported by
Lawan et al. (32) in Pearl millet. The time to 50% anthesis was 1 to 4 days earlier
for the plants from the large-heavy seeds. Summerfïeld et al. (53) stated that in
cowpeas,, the time for flowering is determined exclusively by either mean
temperature or photoperiod, whichever causes the greater delay. In this study the
results clcarly indicate that the size-density of the seeds planted also influenced the
time of flowering.
Pod lcngth was signifïcantly affected by cultivar but not by seed size-density.
(Table 13). The number and weight of seeds per pod were also not significantly
affected by seed size-density (Table 12). The large-heavy seeds, however, produced
signifïcantly more (number and weight) pods per plant than the small-light seeds.

---

42
Table 12. Reproductive development, characteristics and yield of two cultivars of
cowpea.
Parameterl
Seed-Size Density
MS Pinkeye
MS Bunch Purplehull
@vs to First Flower
___________________No
.__________________
Large-heavy
34 Aa
30 Ab
Small-light
36 Ba
33 Bb
Da.ys to 50% Anthesis
Large-heavy
39 Aa
35 Ab
Small-light
40 Ba
39 Bb
Pods/Plant
Large-heavy
11 Aa
11 Aa
Small-light
9 Ba
10 Bb
Pods/Plan t
-~~--~~~~-~-----~---gr~~------~~~~~---~~--
Large-heavy
25.1 Aa
22.8 Ab
Small-light
21.4 Ba
20.7 Bb
&eds/Plant
Large-heavy
20.1 Aa
18.1 Ab
Small-light
16.8 Ba
16.1 Bb
Seeds/Pod
___________________ -No .____________________
Large-hcavy
10.8 Aa
10.0 Ab
Small-light
11.0 Aa
10.0 Ab
Seeds/Pod
-------------------- gr------- ----------m--
Large-heavy
1.96 Aa
1.70 Ab
Small-light
2.06 Aa
1.62 Ab
&ed Yield
___________________ kg/ha ____---__---_
Large-heavy
3918 Aa
3537 Ab
Small-light
3451 Ba
3077 Bb
Pod
- Yield
Large-heavy
4903 Aa
4705 Aa
Small-light
4426 Ba
4155 Ba
100 Seeds Wgt
___________________-__

gr _____________________
Large-heavy
20.05 Aa
17.68 Ab
Small-light
19.93 Aa
17.00 Ab
Parameter means in columns not followed by the same capital letter and in rows
not followed by the same lower case letter differ significantly at the 5% level of
probabili ty according to LSD.

---

43
Table 13. Length, number, and weight of pods per 3 meter row as affected by seed
size-density and cultivar.
Parameter/
Seed Size-Density
MS Pinkeye
MS Bunch Purplehull
Pod Length
__-__----------------cm---------------------
Large-heavy
17.3 Aa
15.9 Ab
Small-light
17.5 Aa
15.5 Ab
Pods/3 m Row
_____________________No,
______ ______________
Large-heavy
330 Aa
331 Aa
Small-light
288 Ba
301 Ba
Pod/3 m Row
_____--__-____------- gr_______________-__-__
Large-heavy
735.4 Aa
705.8 Aa
Small-light
663.9 Ba
623.0 Ba
Parameter means in columns not followed by the same capital letter and in rows
net followed by the same lower case letter differ significantly at the 5% level of
probability according to LSD.

---

44
The large-heavy seeds produced more vigorous plants with slightly more branches
ami an equal number of floral peduncles that were more precocious in flowering,
hence, the greater number of pods/plant. The number of pods per 3 m row was also
significantly higher for the large-heavy seeds (Table 13). Since the average number
of plants harvested per 3 m row was the same for the two seed size-density classes,
tho differences in pod yield between the plots sown with large-heavy and small-
light seeds was primarily due to the higher number and weight of pods per plant
for the former.
The lOO-seeds weight (Table 12) was not significantly affected by seed size-
density. These fïndings are in contrast to those reported by Oliveira (42) who
four-rd that in cowpea, plants from large seeds produced seeds which were
signifïcantly higher 100-seeds weight than those from small seeds. Dharmalinghan
and Ramakrishnan (12) obtained similar results in peanut.
In terms of seed weightia, the yield from the large-heavy seeds was
signifïcantly higher than that from the small-light seeds. These findings are in
agreement with those reported for cotton (26), soybean (18), and Pearl millet (19,
32).
Seed weightia or yield was signifïcantly and positively correlated with pod
weightka (r=0.914), seedling dry weight 15 days after planting (r=0.598), number
of branches per plant (r=0.553), number of pods per 3 m row (r=0.526), number of
floral peduncles per plant (r-=0.520) and the weight of 100-seeds (r=0.508) (Table
14). Since the pod length, number of seeds per pod and the weight of seeds per pod
were not signifïcantly affected by seed size-density and exhibited very little

---

Table 14.
Selected Pearson correlation coeffkients between some of the parameters measured in the seed size-density
study.
SDW 15
SDW 27
NB
NFP
NPP
WPP
NPR
WP/ha
swrha
WlOOS
SDW 15
1.000
0.551*
0.599**
SDW 27
1.000
0.522*
NB
1.000
0.510*
0.50*
0.553*
NFP
1.000
0.580**
0.520*
NPP
1.000
0'.582**
-0.093
WPP
1.000
NPR
1.000
0.526*
WPfha
1.000
0.914**
SWlha
1.000
0.508*
WlOOS
1.000
1’
*
Significant at 0.05 probability level
**
Significant at 0.01 probability level
Code:
SDW15 = Seedling dry weight 15 days after emergence
SSW27 = Seedling dry weight 27 days after planting
N B
= Mean number of branches per plant 46 days after planting
NPP
= Mean number of floral peduncles per plant 46 days after planting
NPP
= Mean number of pods per plant
WPP
= Weight of pods per plant
NPR
= Number of pods per 3 m row.
WP/ha = Weight of pods per 3 m row.
SW/ha = Weight of seeds per ha.
WlOOS = Weight of 100 seeds

---

46
variation, the number of pods per plant was the main variable in determining pod
and seed yield/ha.
General Observations
-
The large-heavy seeds of MS pinkeye and MS Bunch Purplehull cowpea
were higher in vigor than the small-light seeds. Although the large-heavy seeds
germinatcd a bit more slowly, they had a higher percent germination and survival
than did the small-light seeds. Seedling dry matter accumulation 15 and 27 days
after planting was superior for the large-heavy seeds, and plants from them started
flowering 2 to 3 days earlier than those from the small-light seeds. The plants
from large-heavy seeds developed slightly more branches, had more or an equal
number of floral peduncles, and probably more fertile flowers, which developed into
a greater number of pods per plant, which, in turn, resulted in a higher yield/ha
as compared to small-light seeds.
Plant Population (SeedinP- Rate) Effects
Seedling Emergence and Survival
There was no signifïcant difference in field emergence due to seeding rate
or cultivar, and differences in seedling survival at 17 days after planting were
inconsistent and variable due to random depredation by insect pests.
Seedling/Plant Growth
As expected, 29-day plant dry weight was significantly higher for the low
population density as compared to the high population density (Table 15). This
difl%renco cari be attributed to the lesser competition for water, nutrients, light and

---

4 7
Table 15. Growth and development of two cultivars of cowpea in high and low
population density.
-
Parameter/
Plant Density
MS Pinkeye
MS Bunch Purplehull
29-Day Dry Weight
--_-________~__~~ gr ___-____-_____-
High Population
1.81 Aa
3.26 Ab
hw Population
4.36 Ba
5.31 Bb
37-Day Plt Hgt
---------------cm------------------
High Population
16.0 Aa
23.5 Ab
L.ow Population
14.2 Ba
18.2 Bb
47 Days, Branches/Plt
________________No.
_____ __________ __
High Population
1.0 Aa
0.0 Aa
Low Population
3.4 Ba
2.8 Ba
47
- Days, Peduncles/Plt
High Population
4.8 Aa
5.6 Ab
Low Population
13.2 Ba
17.4 Bb
-
Parameter means in columns not followed by the same capital letter and in rows
not followed by the same lower case letter differ signifïcantly at the 5% level of
probability according to LSD.

---

4 8
space among plants in the low density population. Cowpea is an indeterminate,
vining, or semi-vining species and tends to spread throughout, available space (and
resources). Soybean exhibits a similar growth response to plant density (17).
Again, as expected, the number of branches/plant 47 days after planting was
signifkantly higher in the low population as compared to the high population for
probable reasons as previously discussed. The number of branches was negatively
correlated (r-=-0.82) with the number of plants/m”, and positively correlated with
plant dry weight at 29 days (r-=0.717) (Table 16). Plant height at 32 days, however,
was signifïcantly higher in the high population density where the plants tended to
grow upright rather than to “spread out” as did the plants in the low population.
The rapid dry matter accumulation and larger vegetative body of plants in the low
population resulted in significantly more branches per plant (at 46 days) and a
greater number of floral peduncles per plant as compared to plants from the high
population.
Reproductive Development
The number of days from planting to the appearance of the first flower
differed among cultivars but not population densities (Table 17). Similarly, the
50% anthesis stage was reached in the same number of days in both the low and
high populations.
The number of pods per plant was much higher for plants in the low
population than those in the high population. There was no difference in the
pods/plant bctween the cultivars. The correlation between pods/plant and plants
per m” was highly negative (r = -0.965) (Table 16). On the other hand, the number
of pods/plant and the number of branches and peduncle/plant were positively

---

Table 16. Selected Pearson correlation coefficients between some ofthe parameters measured in ihe popuiation densiiy
sîudy.
DW29 B47
P 4 7
H E
PM2
P P
WPP
WSP
PLlH
W S P l H
DW 29
1.000
0.717**
0.751?”
0.740**
B 4 7
1.000
0.824*”
-0.470*
-0.899** 0.850**
0.903**
P47
1.000
0.931””
0.890**
H E
1.000
PM*
1.000
-0.965”*
-0.982**
-0.930**
P P
1.000
WPP
1.000
0.930**
0.520*
WSP
1.000
PLlH
1.000
0.973**
WSPlH
1.000
* Significant at 0.05 probability level; ** Significant at 0.01 probability level
Code
s9 = Seedling dry weight 29 days after planting
B47 = Mean number of branches per plant 47 days after planting
P47 = Mean number of floral peduncles per plant 47 days after planting
HE = Plant height
PM2 = Number of plants per square meter
PP = Mean number of pods per plant
WPP = Weight of pods per plant
WSP = Weight of seed per plant
PLlH = Mean pod length for the first harvest
WSPlH = Mean weight of seeds per pod for the first harvest

---

50
Table 17. Reproductive development and characteristics of two cultivars of cowpea
in high and low population density.
Parameter/
Plant Density
MS Pinkeye
MS Bunch Purplehull
Time to First Flower
____________ --Days __-__--_--..-
High Population
35 Aa
31 Ab
Low Population
35 Aa
33 Ab
Time to 50% Anthesis
High Population
41 Aa
35 Ab
Low Population
40 Aa
37 Ab
Pods/Plant
________________No
.________________
High Population
6 Aa
7 Aa
Low Population
21 Ba
26 Ba
Pods/Plant
___________________ gr _____~-____-_~~~~
High Population
13.4 Aa
14.2 Aa
Low Population
50.6 Ba
49.0 Ba
SeedsE’lan t
High Population
10.4 Aa
9.6 Aa
IJOW Population
38.9 Ba
40.6 Ba
1 OO-Seeds Wgt
High Population
18.2 Aa
16.4 Ab
Low Population
18.6 Aa
16.2 Ab
Paramcter means in columns not followed by the same capital letter and in rows
not followed by the same lower case letter differ signifïcantly at the 5% level of
probability according to LSD.

---

5 1
correlated (r=0.850 and 0.931, respectively), and with the plant dry weight at 29
days (r=0.75 1).
The number of branches and the number of floral peduncles per plant
appeared to be the major components of pod yield/plant. Similar findings have
been reported by Fontes and Ohlrogge (18) for soybean, Grafton et al. (22) for dry
bean, Adams (1) for navy bean, and Westermann et al. (59) for indeterminate type
beans.
Pod length and the number and weight of seeds per pod were significantly
greater on plants grown in the low population density than on those produced
under high population density (Table 18). In the case of the pods, there was a
general decrease in pod length with lateness of the harvest, especially in the case
of MS Pinkeye. There was also a tendency - not statistically verifïed - for the seed
weighllpod to decrease with lateness of the harvest.
The lOO-seeds weight was not affected by plant population density. The
higher yield/plant in the low populations, therefore, was primarily the result of an
increase in the number of pods per plant, rather than in the number of seeds/pod
and the seed weight (wgt000 seeds).
The number and weight of pods per 3 m row were highest for the plants
grown in the high population (Table 19). Although the individual plants in the low
population were much more productive than those in the high population, their
number was too low to fully compensate for the differences in plant density. The
extent of compensation, however, was very great. The number of plants in the low
population were only about 23% of those in the high population, but per unit area
their yield was 75 to 88% that of the high population.

---

5 2
Table 18. Effects of population density, harvest time and cultivar on pod length,
and the number and weight of seeds per pod in cowpea.
Harvestl
Plant Density
MS Pinkeye
MS Bunch Purplehull
First Harvest
__-__-___ pod hngth (cm) --__--_--
High Population
16.7 Aa
14.7 Ab
Low Population
17.5 Ba
15.9 Ba
Second Harvest
High Population
15.4 Aa
13.9 Ab
Low Population
16.2 Ba
15.3 Bb
Th.ird Harvest
High Population
14.0 Aa
15.1 Aa
Low Population
13.8 Aa
14.5 Aa
First Harvest
-------Seeds WgtRod (gr)-------
High Population
1.8 Aa
1.4 Ab
Low Population
2.1 Ba
1.6 B b
Second Harvest
High Population
1.6 Aa
1.2 Ab
Low Population
1.8 Ba
1.6 Bb
First Harvest
__--- --Seeds/Pod (NO.)--------
Iligh Population
1 0 Aa
9 Ab
Low Population
11 Ba
10 Bb
Second Harves t
High Population
9 Aa
7 Ab
Low Population
10 Ba
10 Bb
Parameter means in columns not followed by the same capital letter and in rows
not followed by the same lower case letter differ signifïcantly at the 5% level of
probability according to LSD.

---

5 3
Table 19. Number and weight of pods and number of plants per 3 meter row for
two cultivars of cowpea in high and low plant density.
Characteristicf
Plant Density
MS Pinkeye
MS Bunch Purplehull
Pods/3 m Row
_______--_________-
No .____-__-_--..-..--a--
Iligh Population
368 Aa
455 CAb
Low Population
292 Ba
308 Bb
Pods/3 m Row
_______-___________ gr ____________-___--
High Population
805 Aa
838 Aa
IAW Population
709 Ba
652 Ba
Plants/3 m Row
1 Iigh Population
6 0
60
hw Population
1 4
1 2
Parameter means in columns not followed by the same capital letter and in rows
not followed by the same lower case letter differ signifïcantly at the 5% level of
probability according to LSD.

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5 4
Seed Size Distribution
Size distribution of the harvested seeds was affected by plant population and
cultivar (Tables 20 and 21). Seeds produced in the high population were slightly
smaller than those produced in the low populations. It should be recalled that both
the number and weight of seeds/pod were higher on plants in the low population.
General Observations
The cowpea plant responded to the increase in available space in terms of
vegetative and reproductive development. Plants in the low plant population had
more vegetative branches and floral peduncles and produced longer pods with more
seeds per pod and more pods per plant than did those from the high population
community. The difference in the number of plants per unit area between the high
population (60 plants/3 m row) and low population (14 plants/3 m row) was SO
great, however, that it overrode the “compensation” potential of plants in the low
population for production.

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5 5
Table 20. Size distribution (cumulative) of seeds of two cultivars of cowpea
produced in high and low density populations.
Seed Size/
Plant Density
MS Pinkeye
MS Bunch Purplehull
__________ % (cumulative)---------
> IfY64 Inch
High Population
27.6 Aa
10.8 Ab
Low Population
38.5 Ba
11.1 Bb
~ > 17/64 Inch
High Population
69.6 Aa
46.6 Ab
Low Population
77.6 Ba
50.4 Bb
> 16/64 Inch
High Population
92.2 Aa
81.4 Ab
Low Population
94.3 Aa
81.7 Ab
> 15/64 Inch
I Iigh Population
96.9 Aa
94.2 Ab
Low Population
97.8 Aa
94.6 Ab
Parameter means in columns not followed by the same capital letter and in rows
not foilowed by the same lower case letter differ significantly at the 5% level of
probabili ty according to LSD.

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56
Table 21. Size distribution (incremental) of seeds of two cultivars of cowpea
produced in high and low density populations.
Seed Size/
Plant Dcnsity
MS Pinkeye
MS Bunch Purplehull
_-____-- s (incremental) ________
>19/64 Inch
Iiigb Population
3.4 Aa
0.6 Ab
Low Population
6.2 Ba
0.9 Bb
<19/64 >18/64 Inch
High Population
24.6 Aa
10.2 Ab
Low Population
33.4 Ba
13.7 Bb
<18/64 >17/64
High Population
41.6 Aa
35.6 Ab
Low Population
39.1 Aa
37.6 Ab
< 1’7164 > 16164
High Population
21.8 Aa
34.8 Ab
Iow Population
16.4 Ba
32.8 Bb
<16/64 >15/64 Inch
High Population
5.4 Aa
12.9 Ab
Low Population
3.2 Ba
10.4 Bb
<15/64 >14/64 Inch
High Population
1.9 Aa
3.9 Ab
Low Population
1.1 Ba
3.2 Bb
< 14/64 Inch
High Population
1.3 Aa
2.0 Ab
140~ Population
0.8 Ba
1.4 Bb
Parameter means in columns not followed by the same capital letter and in rows
net followed by the same lower case letter differ significantly at the 57~ level of
probabili ty according to LSD.

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CHAPTER VI
SUMMARY AND CONCLUSIONS
The objectives of these studies were to establish the effects of planting date,
seed size-density, and population density in cowpea on vegetative and reproductive
growth and development. Two widely grown cultivars of cowpea were used:
Mississippi Pinkeye and Mississippi Bunch Purplehull. Seeds for the several
studies were obtained from crops produced on the MAFES Plant Science Farm in
1989 and 1990. Pods were hand harvested after the physiological maturity stage,
carefully dried and hand threshed. The threshed seeds were cleaned with an air-
screen cleaner and stored at 10°C and 50% RH until needed for the various
experiments.
Four field plantings were made for the time of planting study to broadly
sample the various environmental conditions under which cowpea is grown in
Mississippi. The planting dates were May 30, June 21, July 12, and August 4,
1990. 111 the case of the seed size-density study, small-light and large-heavy seeds
of the two cultivars were planted in the field June 14, 1991. The population
density study (60 and 15 plants per 3 m row) was also planted June 14, 1991.
The effects of planting date on growth and development of cowpea were
primarily environmental. The major environmental factors such as temperature,
solar radiation and water supply varied substantially among the planting dates.
5 7

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5 8
These factors, individually and interactively, affected emergence, seedling growth,
and the components of yield: number of plants per unit area; pods/plant; and
seeds/plant. Pod length and seed weight did not differ among planting dates.
Generally, yields were highest for the June plantings (May 30 and June 21) and
lowest for the August 4 planting. The low yields in the later plantings appeared
to be related primarily to low water supply and cool night temperatures.
Plant growth and development were signifïcantly affected by the size-density
of the seeds planted. The large-heavy seeds were much more vigorous than the
sm.all-light seeds and this superior vigor was translated into more rapid and
greater vegetative and reproductive growth and development. The plants from
large-heavy seeds developed more branches, more floral peduncles, and more
flowers which produced more pods/plant and yield/ha than those from small-light
seeds. Flowering in plants from the large-heavy seeds was also 2-3 days earlier as
compared to those from small-light seeds.
In the plant population density study, the plants responded positively to the
increase in available space in terms of vegetative and reproductive development.
Plants in the low population communities had more vegetative branches and floral
peduncles ?? nd produced larger pods with more seeds per pod and pods per plant
than did those in the high population communities. The difference in the number
of plants per unit area between the low (15 plants/3 m row) and high (60 plants/3
m row) populations was SO great, however, that it overrode the “compensation”
potential of the plants in the low population for production.

---

5 9
On the basis of the results obtained in these studies, the following
conclusions cari be drawn:
1 .
Growth and reproduction in cowpea was significantly affected by
planting date due primarily to differences in the aowing
environments arnong planting dates, e.g., temperature, solar
radiation and water supply.
2.
The large-heavy seeds from seed populations of two cowpea cultivars
were signifkantly more productive in terms of vegetative and
reproductive growth and development than the small-light seeds.
3.
Cowpea had great capacity to compensate in terms of growth and
reproduction for differences in population density, but this capacity
was insuffkient to equalize biomass production between the extreme
population densities examined: 60 plants/3 m row vs. 15 plants/3 m
row.

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