Table of Contents
Bubenheim, D.L., C.A. Mitchell, and S.S. Nielsen. 1990. Utility of cowpea
foliage in a crop production system for space. p. 535-538. In: J. Janick and
J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.
Utility of Cowpea Foliage in a Crop Production System for Space
David L. Bubenheim, Cary A. Mitchell, and Suzanne S. Nielsen
- EXPERIMENTAL METHODS
- Dry Weight Accumulation
- Biomass Partitioning
- Seed and Pod Yield
- Yield Efficiency
- Nutritional Composition
- Table 1
- Table 2
- Table 3
- Table 4
Controlled Ecological Life Support Systems (CELSS) will utilize green plants to
supply food, oxygen, and purified water for inhabitants of future spacecraft
and planetary bases. Candidate crop plants are selected for yield optimization
research based on potential contribution to a well-balanced vegetarian diet,
low-volume canopy characteristics, and short life-cycle duration.
Cowpea (Vigna unguiculata) is a candidate crop for CELSS because of the
low-fat, high-complex carbohydrate, moderate protein characteristics of the
edible portion. The seeds ("black-eyed peas") are considered the edible form
of the plant in the United States, but the leaves serve as a major staple in
the diet throughout Africa and Asia (Bittenbender et al. 1984). Young leaves
or shoot tips are harvested and consumed as cooked greens or dried for storage.
Harvest strategies practiced in the field to utilize foliage include harvest of
the entire vegetative plant prior to flowering or partial defoliation and later
seed harvest from the same plants.
Utilization of cowpea as a leafy vegetable and grain crop may provide
nutritional and harvest versatility not available with purely vegetative crops
like lettuce or monocarpic crops like wheat (Bubenheim and Mitchell 1987,
1988). A purely vegetative system of cowpea might be desirable in a CELSS.
Only one phase of the life cycle need be satisfied in a vegetative system, that
is, peculiar environmental requirements during any single developmental phase
would not complicate the system. Vegetative culture of cowpea, a short-day or
day-neutral plant for flowering, could be accommodated with the long
photoperiod and high photosynthetic photon flux optimizing environments
required for some long-day candidate crops. The nutrient composition of cowpea
foliage is more desirable than that of many vegetative crops and cowpea could
provide dietary versatility by utilization of either foliage or seeds from the
same crop species.
The ultimate efficiency and feasibility of a CELSS will be evaluated on the
basis of productivity of the system per unit inputs necessary to operate the
system. The inputs of the final CELSS will be volume, mass, time, and energy
In the early stages of yield optimization with cowpea, we considered time and
area inputs and evaluated yield efficiency on a daily basis per unit area.
Since both cowpea foliage and seed are edible, and since both plant parts are
utilized in field agriculture, productivity and yield efficiency were
determined for cowpea following three different harvest strategies. Harvest of
the whole, vegetative plant prior to flowering, traditional seed harvest, and a
combination of removal of young leaves and eventual seed harvest from the same
plants were evaluated. Nutritional composition of the edible plant parts also
Two cowpea cultivars 'Bainkey-21' and 'IT84E-124' were grown using soilless
culture in a greenhouse at Purdue University. All plants were exposed to a
10-hour photoperiod by enclosing the plants in a light exclusive curtain during
each dark period. Temperature was maintained at 21 ± 5°C.
In the vegetative harvest treatment, whole plants (except roots) were harvested
at 15-day intervals beginning 10 days after germination. At each harvest, 4
plants of each cultivar were separated into leaves, petioles, and stems of
individual branches. All leaves present on a plant at each vegetative harvest
were considered edible. For the traditional seed-harvest treatment, only dried
seed was considered the edible portion of the plant. The combination treatment
of vegetative and seed harvest from the same plants consisted of removal of 2
to 4 recently formed trifoliolate leaves (not fully expanded) from each branch
on a plant 25 and 40 days after germination, and then seed was harvested from
those same plants. Carbohydrate, protein, fat, and ash content were determined
for leaves and seeds of harvested plants.
A similar pattern of dry weight accumulation was exhibited by both cowpea
cultivars, although each exhibited a different growth habit (Chaturvedi 1980).
'Bainkey-21' developed vigorous vining branches, whereas 'IT84E-124' exhibited
a determinate growth habit and developed a compact, low-volume canopy As
typical for cowpea, leaf dry weight decreased in support of pod development for
both cultivars (Ezedinma 1973, Huxley and Summerfield 1976, Stewart et al.
1978). Biomass production was greatest and a larger proportion of biomass was
partitioned to foliage by 'IT84E-124' compared with 'Bainkey'. Data presented
are for 'IT84E-124' only.
Removal of young expanding leaves during the vegetative phase just prior to
flowering as part of the vegetative/seed-harvest strategy suppressed total
plant biomass and altered partitioning compared with plants in a traditional
seed-harvest strategy (Table 1). Periodic, partial defoliation stimulated leaf
production; 68% of cumulative biomass was in the form of leaves compared with
57% for vegetative plants. Twice as much cumulative leaf dry weight was
produced by plants in the vegetative/seed-harvest strategy than by plants in
the traditional seed-harvest strategy.
The suppression of biomass accumulation and diversion to the vegetative portion
of the plant resulting from vegetative/seed harvest was unaffected by harvest
strategy (Table 2); seed was harvested from plants of both the vegetative/seed
and traditional seed-harvest strategies 75 days after germination. Seed yield,
seed number, and pod number per plant were, however, severely suppressed as a
result of partial defoliation. While the reduction in source leaves limited
reproductive sink size (seed number per plant), individual seed size was not
affected. The mixed-harvest scenario of seed + leaves together increased the
time to harvest by 2 days.
Yield efficiency was greatest for the vegetative harvest strategy with
whole-plant harvest 40 days after germination (Table 3). While total edible
yield per plant was equal for the vegetative and traditional seed-harvest
strategies, the vegetative product could be harvested 35 days earlier than the
75 days required to produce seeds. Daily yield per plant, yield per unit area,
and overall yield efficiency (g m-2 day-1) were two to three times greater for
the vegetative strategy than for the traditional seed-harvest strategy,
reflecting the shorter time to harvest and smaller plant size. Of the three
harvest strategies considered, the vegetative/seed harvest was identified as
the least efficient. Total edible yield per plant and daily area, and over-all
yield efficiencies were significantly less for the vegetative/seed-harvest
strategy than for either the purely vegetative or traditional seed-harvest
In areas of the world where the vegetative/seed-harvest strategy is practiced,
the primary goal appears to be timely availability of food rather than
production of an absolute maximum amount. Final seed yield is sacrificed so
that food in the form of cowpea foliage is provided throughout the season.
Harvest index, the cumulative edible biomass expressed as a percent of total
plant biomass, was greatest for the vegetative/seed strategy, the least
efficient strategy of those considered. While increased harvest index is a
characteristic of enhanced yield it cannot be used as a sole indicator of yield
potential. The potential for yield enhancement in cowpea grown under
optimizing environments will be evaluated further. Both traditional seed
harvest and purely vegetative harvest strategies will be used in future
Leaf carbohydrate content increased with leaf age, but was greatest in the seed
(Table 4). Protein content of older leaves was similar to that of seeds;
protein content of young leaves was greatest. Fat content was greater in leaf
tissue than in seed and was not affected by leaf age. Inorganic mineral (ash)
content of cowpea foliage was much greater than that for seed regardless of
Cowpea is a dynamic crop that may add versatility to the diet not provided for
by other candidate crops for CELSS. Cowpea could complement a large number of
other food crops by utilization of two different edible plant parts (leaves and
seeds), each with different nutritional characteristics. A single cowpea crop
should be grown to supply either leaves or seeds as the yield efficiency was
suppressed by the combination of leaf and seed harvest. Yield efficiency was
greatest for the vegetative harvest strategy, but the bioavailability of
nutrients from foliage must be determined before potential use of this strategy
can be adequately evaluated. Both leaves and seeds of cowpea appear to provide
a low-fat high-protein food choice. By choosing leaves of various ages or
seed, the proportion of carbohydrate and protein provided in the diet by cowpea
could be controlled. Cowpea is a versatile legume crop that will provide high
carbohydrate together with moderate protein and low fat from foliage as well as
seeds for a vegetarian diet in a space-deployed bioregenerative life support
system. The results of this study suggest that some plants could be grown for
reproductive harvest while separate plants should be dedicated to vegetative
harvest. Additional work is required to find a mixed-harvest scenario from the
same plant that will be as productive.
- Bittenbender, H.C, R.P. Barrett and B.M. Indire-Lavusa. 1984. Beans and cowpeas
as leaf vegetables and grain legumes. Monograph no. 1, Bean/Cowpea
collaborative research support program, East Lansing, MI.
- Bubenheim, D.L. and C.A. Mitchell. 1987. Evaluation of new candidate crop
species for CELSS. Proc. Space Life Science Symposium: Three Decades of Life
Science Research in Space. Washington, DC. 1:27.
- Bubenheim, D.L. and C.A. Mitchell. 1988. Cowpea harvest strategies and yield
efficiency for space food production. HortScience 23:106. (Abstr.)
- Chaturvedi, G.S, P.K. Aggarwal, and S.K. Sinha. 1980. Growth and yield of
determinate and indeterminate cowpeas in dryland agriculture. Agric. Sci. Camb.
- Ezedinma, F.O.C. 1973. Effects of defoliation and topping on semi-upright
cowpeas ]Vigna unguiculata (L.) Walp.] in a humid tropical environment.
Exp. Agric. 9:203-207.
- Huxley, P.A. and R.J. Summerfield. 1976. Leaf area manipulation with vegetative
cowpea plants [Vigna unguiculata (L.) Walp.]. J. Exp. Bot.
- Stewart, K.A, R.J. Summerfield, and B.J. Ndunguru. 1978. Effects of source-sink
manipulations on seed yield of cowpea [Vigna unguiculata (L.) Walp.]. I-
Defoliation. Trop. Agric. 55:117-125.
Table 1. Biomass production and partitioning for three harvest systems
of cowpea cv. IT84E-124.
zMean separation in columns by Waller-Duncan K-test (K=100), or F-test.
| ||Yield (g/plant)|
|Harvest system ||Leaves ||Stem ||Pod ||Seed ||Total|
|Seed (75 days) ||23.8b(c)z ||28.2a ||46.5a ||34.6a ||117.3a(a)|
|Vegetative (40 days) ||33.8a(b) ||20.4b || || ||59.8b(c)|
|Vegetative + seed (75 days) ||7.1c (46.5a)y ||11.9c ||12.7b ||10.1b ||33.9c (68.5b)y|
yIncludes leaves from vegetative harvests.
Table 2. Yield of cowpea cv. IT84E-124 as influenced by harvest
zMean separation between rows by F-test at 1% (**), 5% (*) level or not
|Harvest system ||(No.) ||(g/plant) ||(g/seed) ||Pods (no.) ||Days to|
|Seed ||34.6 ||238.5 ||0.15 ||54.6 ||37|
| ||**z ||** ||NS ||** ||*|
|Vegetative + seed ||10.1 ||66.0 ||0.15 ||15.2 ||39|
Table 3. Yield characteristics of cowpea cv. IT84E-124 as influenced
by harvest system.
zMean system within rows by Waller-Duncan K-test (K = 100) or F-test.
| ||Harvest system|
|Plant part ||Seed ||Vegetative ||Vegetative|
|Seed yield (g/plant) ||34.6az || ||10.1b|
|Edible leaves (g/plant) || ||33.8z ||14.8 b|
|Total edible yield (g/plant) ||34.6ay ||33.8az ||25.0b|
|Harvest index (%) ||30c ||58b ||72a|
|Days to harvest ||75a ||40b ||75a|
|Daily yield (g/day-plant) ||0.46b ||0.85a ||0.33c|
|Area yield (g/m2 canopy area) ||69.2b ||105.4a ||45.6c|
|Yield efficiency (g/m2-day) ||0.92b ||2.64a ||0.60c|
yAssumes all harvested leaves are edible at day 40.
Table 4. Proximate analysis of leaves and seeds of cowpea cv.
zMean separation with row by Waller-Duncan K-test (K=100).
| ||Yield (% dry wt)|
|Plant part ||Carbohydrate ||Protein ||Fat ||Ash|
|Expanding leaves (7-10 days old) ||31.8cz ||43.0a ||5.3a ||14.4a|
|Expanded leaves (22-25 days old) ||42.6b ||30.5b ||5.0a ||14.8a|
|Seed ||55.5a ||30.9b ||1.2b ||3.8b|
Last update March 31, 1997