Nativa, Sinop, v. 10, n. 4, p. 577-584, 2022.
Pesquisas Agrárias e Ambientais
DOI: https://doi.org/10.31413/nativa.v10i4.13820 ISSN: 2318-7670
Water demand and technical-economic viability of cowpea grown
in different production scenarios
Francisco Edson Paulo FERREIRA1*, Vicente de Paulo Rodrigues da SILVA1
1Universidade Federal de Campina Grande, Campina Grande, PB, Brasil.
*E-mail: edsonjua2009@gmail.com
(ORCID: 0000-0003-2197-7761; 0000-0003-4914-4833)
Submitted on 2022/05/12; Accepted on 2022/12/05; Published on 2022/12/16.
ABSTRACT: Water demand and agronomic and economic efficiency of cowpea are strongly related to
agricultural practices and climatic conditions. This study aimed to determine in which cropping season cowpea
has the highest water demand and maximum agronomic and economic efficiency as a function of water stress
under the edaphoclimatic conditions of the semi-arid region of northeastern Brazil. Cowpea was cultivated in
two cropping seasons (rainy and dry) and subjected to five forms of water stress (without water stress, water
suspension for 5, 10 and 15 days and rainfed cultivation) and four replicates, started in the flowering and grain
filling stages, under no-tillage system. Agronomic (yield, biomass, harvest index and water use efficiency) and
economic (gross revenue, net revenue, rate of return and profit margin) parameters were evaluated. The water
demand of cowpea in the dry season was 20.2% higher than in the rainy season; consequently, the Kc values
obtained were also higher in this period. The climatic conditions that occurred during the cropping seasons and
water stress negatively influenced the agronomic performance and financial profitability of cowpea, being more
evident in the rainfed cultivation. For the edaphoclimatic conditions of the study, cowpea can be grown without
significant losses of yield and profitability in both cropping seasons, provided that the water stress does not last
more than 10 days during its reproductive stage.
Keywords: profitability; Vigna unguiculata; water stress; cropping season.
Demanda hídrica e viabilidade técnico-econômica do feijão-caupi cultivado em
diferentes cenários produtivos
RESUMO - A demanda hídrica e a eficiência agronômica e econômica do feijão-caupi estão fortemente
relacionados com as práticas agrícolas e a condições climáticas. Este trabalho teve como objetivo determinar
em qual época de cultivo o feijão-caupi apresenta maior demanda hídrica e máxima eficiência agronômica e
econômica em função do estresse hídrico, nas condições edafoclimáticas da região semiárida do nordeste do
Brasil. O feijão-caupi foi cultivado em dois períodos de cultivo (chuvoso e seco) e submetido a cinco formas
de estresse hídrico (sem estresse hídrico, suspensão de água de 5, 10 e 15 dias e plantio de sequeiro) com quatro
repetições, iniciado nas fases de floração e enchimento de grãos, em sistema de plantio direto. Foram avaliados
parâmetros agronômicos (produtividade, biomassa, índice de colheita e eficiência do uso da água) e econômicos
(renda bruta, renda líquida, taxa de retorno e margem de lucro). A demanda hídrica do feijão-caupi no período
seco foi 20,2% superior a do período chuvoso, consequentemente, os valores de Kc obtidos também foram
superiores nesse período. As condições climáticas ocorridas nos períodos de cultivos e o estresse hídrico
influenciaram negativamente no desempenho agronômico e rentabilidade financeira do feijão-caupi, sendo mais
evidenciada no cultivo de sequeiro. Para as condições edafoclimáticas do estudo, o feijão-caupi pode ser
cultivado sem significativas perdas de produtividade e rentabilidade em ambos os períodos de cultivo, desde
que o estresse hídrico não seja superior a 10 dias durante sua fase reprodutiva.
Palavras-chave: rentabilidade; Vigna unguiculata; estresse hídrico; época de cultivo.
1. INTRODUCTION
Among all economic activities, agriculture is considered
the activity that most depends on environmental conditions,
especially climatic conditions. Agricultural crops, when
poorly supplied with water and subjected to high
temperatures, cannot achieve their full development, causing
yield losses and, consequently, lower profits for the
agricultural sector (FÉLIX et al., 2020).
In the Northeast region of Brazil, cowpea cultivation
assumes great socioeconomic importance, as in general it is
practiced by small family farmers, since cowpea is considered
a subsistence crop, is an important component in production
systems and is one of the main sources of income and
employment for the region, and also for its high nutritional
value (FREIRE FILHO et al., 2005). The cowpea crop is
characterized mainly by its rusticity, good adaptation to the
semi-arid climate and its high nutritional value (MELO et al.,
2022).
However, family farming faces major problems to
achieve high yield, and this is mainly due to the fact that
farmers are not able to exploit the production potential of the
crop due mainly to the spatial-temporal variability of rainfall.
In addition, there is still a lack of adoption of minimal
techniques that enhance the increase in crop yield, such as
Water demand and technical-economic viability of cowpea grown in different production scenarios
Nativa, Sinop, v. 10, n. 4, p. 577-584, 2022.
578
the use of irrigation and varieties that are more resistant to
drought (ABREU ARAÚJO et al., 2019; LOPES et al., 2019).
Water scarcity is the main condition that interferes with
crop yield in the semi-arid region. Therefore, prior
knowledge on the agroclimatic requirements of crops
adequately assists agricultural planning, aiming to achieve
greater yield, profitability and reduction of losses due to
climatic factors, with temperature and precipitation being the
climatic elements that most affect common bean
development (LACERDA et al., 2010). In the case of
cowpea, in the flowering and grain filling stages, water stress
tends to drastically reduce its yield (SOUZA et al., 2015;
ALMEIDA et al., 2019).
Thus, it is crucial to know in detail the water need of
cowpea crop in order to maximize the production potential
and minimize production costs, thus improving the
management of available water resources, especially where
they are scarce (MURGA-ORRILLO et al., 2016). The
cowpea crop has a short cycle and, because of this, it is greatly
influenced by droughts and dry spells, and even excess water
can severely affect its growth, so it is indispensable to
perform an adequate management of the crop in order to
satisfactorily meet its water demand (FREITAS et al., 2014;
ABREU ARAÚJO et al., 2019).
Many studies have been conducted to assess the influence
of agricultural practices and climatic conditions on the yield
and economic efficiency of cowpea (CASTRO JÚNIOR et
al., 2015; SILVA et al., 2016; ANDRADE JUNIOR et al.,
2018). In this context, the objective of this study was to
determine in which cultivation time cowpea has maximum
agronomic and economic efficiency as a function of water
stress under the edaphoclimatic conditions of the semi-arid
region of northeastern Brazil.
2. MATERIAL AND METHODS
This study was conducted at the Experimental Station
(EstAgro) belonging to the Academic Unit of Atmospheric
Sciences (UACA) of the Federal University of Campina
Grande - UFCG, in the state of Paraíba, at the coordinates
07° 13’ 50” S latitude and 35° 52’ 52” W longitude and 526
m altitude. The soil of the area has a sandy texture. According
to Coelho; Soncin (1982), based on Köppen’s climate
classification adapted to Brazil, the state of Paraíba has a
mesothermal subhumid climate, with well-defined dry season
(4 to 5 months) and rainy season (autumn to winter).
Two experimental campaigns were carried out, the first
from February 2 to May 14, 2021 (rainy season), and the
second from September 1 to November 9, 2021 (dry season).
The environmental conditions during the experimental
periods were obtained daily, and their mean values are shown
in Figure 1. Water stress in the reproductive stage began on
March 29 and ended on April 12, 2021, in the rainy season,
and began on October 19 and ended on November 2, 2021,
in the dry season.
Cowpea was cultivated in two cropping seasons (rainy
and dry) and subjected to five forms of water stress (without
water stress, water suspension for 5, 10 and 15 days and
rainfed cultivation), under no-tillage system. The
experimental area had 10 masonry beds with dimensions of
8 m x 1 m. Each experimental plot was composed of one bed.
In plots that received water deficit treatments, irrigation was
suspended in the flowering stage of the crop, period in which
70% of the plants had at least one flower.
Figure 1. Climatic data observed during the experiments.
Figura 1. Dados climáticos observados durante a condução dos
experimentos.
Before planting the crop, a chemical-physical analysis of
the soil was performed in the 0-20 cm layer of the profile, for
chemical characterization, and the results were: pH in water-
6.2; organic matter – 11.12 g.kg-1; base saturation (V) –
68.75%; Na+, H+Al3+, Ca2+ and Mg2+ - 0.04, 2, 2.27, and 1.7
cmolc.dm-3; and P and K+ - 30.95 mg.dm3 and 142.51
mg.dm3, respectively. The soil of the area has sandy texture
and its values of water content at field capacity (-0.01 Mpa)
and permanent wilting point (-1.5 Mpa), considering the 0-
0.4 m layer, were 7.3% and 4.6% on a volume basis,
respectively.
Sowing was carried out manually, after opening the holes
with a hoe, at spacing of 0.5 m between rows and 0.5 m
between plants, placing 3 to 4 seeds per hole and leaving only
3 plants per hole, which resulted in a planting density of
120,000 plants ha-1.
Water replacement was based on 100% crop
evapotranspiration (Etc), which was estimated according to
Bernardo, Soares e Mantovani (2006), with Kc values of
cowpea determined by Silva et al. (2016) and reference
evapotranspiration (ET0) estimated using the equation
proposed by Allen et al. (1998). The data required to estimate
ET0 were collected daily through an automatic
agrometeorological station (Irriplus, E5000 model) installed
in the experimental area.
Irrigation was applied by a drip system with flow rate of
4.5 L.h-1 at a service pressure of 2 kgf. Cm-2 and adopting a
90% application efficiency, and the system had two lines per
bed and one dripper per hole. A two-day interval between
irrigations was adopted. Irrigations were always carried out
during the morning, between 06h and 08h, and when rainfall
volume did not exceed the water demand of the crop.
The cowpea variety cultivated was ‘Costela de vaca’
(Heirloom), due to its acceptance by family farming in the
Northeast region of Brazil (SILVA; NEVES, 2011). This
cultivar has a semi-prostrate growth habit, its flowering
begins at 40 days after sowing, and its maturity is reached
between 71 and 80 days after sowing. Its average yield is
generally more than 1,000 kg ha-1 under rainfed regime
(SANTOS; LIMA, 2015).
During the stay of the crop in the field, manual weeding
was carried out to control spontaneous plants, whereas
insects and diseases were controlled using agroecological
practices and alternatives aiming at an agrochemical-free
production. Etc was determined using equation proposed by
Libardi (1995):
24
25
26
27
28
29
0
20
40
60
80
100
120
140
160
Temperature (°C)
Precipitarion and ETo (mm)
P (mm) ET0 (mm/day)
Ferreira; Silva
Nativa, Sinop, v. 10, n. 4, p. 577-584, 2022.
579
ET= P + I ±
± Δs ± R (01)
where: ETc - Crop evapotranspiration (mm/day); P - Precipitation
(mm/day); I - Irrigation; Δs - Water storage variation in the soil
profile; R - Surface runoff; D/A - Deep drainage or capillary rise.
Soil moisture was monitored using a capacitance probe,
diviner 2000® model. Precipitation (P) was collected daily at
the Irriplus Automatic Meteorological Station, irrigation (I)
through irrigation monitoring, while surface runoff (R) and
deep drainage/capillary rise (D/A) were considered null as
the bed area is relatively small and irrigation is carried out
only according to the water need of the crop and moistening
the soil only up to the root system.
Water storage variation in the soil profile (Δs) was
determined by the difference between the values of the initial
(Ɵ1) and final (Ɵ2) water contents, considering the maximum
depth of the crop root system (ZWB), which was 40 cm,
through equation:
∆S = (θ − θ) . Z (02)
where: ∆S: Water storage variation on the days considered (mm); 𝜃2:
Soil water content found at time 2 (final), m3.m-3; 𝜃1: Soil water
content found at time 1 (initial), m3.m-3; ZWB: Depth considered for
water balance (0.4 m).
The Kc values of cowpea cv. ‘Costela de vaca’ were
estimated for the treatment that did not suffer water
restriction through equation (3), according to Doorenbos e
Pruitt (1977). The crop cycle was divided into development
stages as proposed by Allen et al. (1998), and the details to
obtain it are described in Murga-Orrillo et al. (2016), through
equation:
K= ET/ET (03)
where: Kc - crop coefficient; ETc - crop evapotranspiration (mm);
ETo - reference evapotranspiration (mm).
Evaluations of agronomic characteristics were performed
as each plot reached physiological maturity. The following
agronomic characteristics were evaluated in each treatment:
grain yield (quantified by the weight of dry grains harvested
in a usable area of the plot of 1m², expressed in kg.ha-1);
biomass (obtained by weighing the plant shoots, excluding
pods, expressed in kg.ha-1); harvest index (measured by the
ratio between dry grain yield and biomass, expressed as a
percentage) and; water use efficiency, determined by the ratio
between grain yield and the total water depth applied
(irrigation + precipitation), expressed in kg.ha-1.mm-1.
In both experiments, production costs were determined
and the following economic indicators were calculated: gross
revenue (GR) expressed in Reais, determined by multiplying
the dry grain yield of each treatment by the product value
paid to the producer of the region in June 2021, which was
R$ 3.38 per kg of dry grain, and in December 2021, which
was R$ 5.11 per kg of dry grain, with the values practiced
obtained based on the data of Conab (National Supply
Company); net revenue (NR) expressed in Reais, obtained by
subtracting the production costs (PC) from the gross revenue
(GR); rate of return (RR) expressed in Reais, determined by
the ratio between the total revenue and production costs
(PC), a variable that represents how many Reais are obtained
in exchange for each Real applied in the system; profit margin
(PM), obtained by the ratio between net revenue and gross
revenue. The methodology used to calculate these indicators
was recommended by Bezerra Neto et al. (2010).
Calculation was performed considering that the
production costs (PC), such as soil tillage, planting, cultural
practices, harvest, among others, were variable for all
treatments, and that the irrigation system was already in full
operation in the field, to evaluate only the variable cost of the
water depth, because the variation in the volume of water
applied does not influence the cost of the initial investment
with the irrigation project.
The agronomic and economic data obtained were
subjected to analysis of variance and, when there was
significant effect for water stress, regression analyses were
performed, and their significance was checked by the
correlation coefficient through the F test at 5% probability
level, considering the means fitted when R²>0.7. The
analyses were performed using PAleontological STatistics
software version 3 (PAST 3) (HAMMER, 2017).
3. RESULTS
The cycle of cowpea cv. ‘Costela de vaca’ in both
cropping seasons was completed at 70 days, distributed as
follows: 13 days (Stage I); 28 days (Stage 2); 13 days (Stage
III) and 16 days (Stage IV), showing a cumulative total ETo
of 291.6 mm in the rainy season and 327.7 mm in the dry
season, which represented a 20.2% increase in crop water
demand in this period (Table 1). The highest values of ETo
and ETc were observed in stage II. According to Silva et al.
(2016), this behavior can be explained by the greater
development of plants, as the crop has a greater increase in
leaf area and, consequently, increase in its evapotranspiration.
Table 1. Duration of initial (I), vegetative development (II),
flowering/reproductive (III) and final (IV) phenological stages of
cowpea crop and values of reference evapotranspiration (ETo),
crop evapotranspiration (ETc) and crop coefficient (Kc) for each
stage.
Tabela 1. Duração dos estádios fenológicos, inicial (I),
desenvolvimento vegetativo (II), floração/reprodutivo (III) e final
(IV) da cultura do feijão-caupi e valores da evapotranspiração de
referência (ETo), evapotranspiração da cultura (ETc) e o coeficiente
de cultivo (Kc) para cada estágio.
Stage
Rainy Season Dry Season
Duration
(days)
ET
0
(mm)
ETc
(mm)
Kc
ET
0
(mm)
ETc
(mm)
Kc
I 13 63.7 54.1
0.8
5
62.3 55.4
0.8
9
II 28 122.4
118.7
0.9
7
125.2 127.7
1.0
2
III 13 49.0 45.6
0.9
3
60.9 59.1
0.9
7
IV 16 56.5 49.2
0.8
7
79.3 73.0
0.9
2
Total
70 291.6
267.6 - 327.7 315.2 -
For the water use efficiency of cowpea, maximum WUE
was observed in the rainy season (Figure 2) in the treatments
that received irrigation (greater than 5.7 kg ha-1 mm-1), while
in the rainfed treatment, the WUE was only 2 kg ha-1 mm-1.
In the dry season, the WUE was lower than 5 kg ha-1 mm-1
in all irrigated treatments, but in the rainfed treatment, the
WUE was 21 kg ha-1 mm-1. Certainly, agricultural practices of
mulching and no-tillage in the cultivation of cowpea, even
subjected to water stress, contributed to better water use
efficiency in both cropping seasons.
Water demand and technical-economic viability of cowpea grown in different production scenarios
Nativa, Sinop, v. 10, n. 4, p. 577-584, 2022.
580
Figure 2. Yield, biomass, harvest index and water use efficiency of cowpea as a function of water stress cultivated in rainy season (A, B, C,
D) and dry season (E, F, G, H), respectively. R²- coefficient of determination; *significant and ns not significant by F test at 5% probability
level.
Figura 2. Produtividade, biomassa, índice de colheita e eficiência do uso da água do feijão-caupi em função do estresse hídrico cultivado em
período chuvoso (A, B, C, D) e período seco (E, F, G, H), respectivamente. R²- coeficiente de determinação; *significativo pelo teste F a
5% de probabilidade.
Significant decreasing linear responses were observed in
all economic viability indicators (Figure 3). However, these
linear correlations between economic indicators and the
effect of water stress for cowpea cultivation in the dry season
have values below 0.7, but with high statistical significance.
This suggests that the profitability of cowpea was affected
more strongly by water restriction, and these reductions were
more evident in the rainfed cultivation system. However, the
profitability of cowpea cultivated under rainfed regime can
be increased if it is intercropped with other crops, such as
corn, due to the positive return of net revenue and the rate
of return (CARVALHO et al., 2017).
Therefore, in the present study, it was verified that the
climatic conditions that occurred in the cropping seasons and
water stress influenced the agronomic performance and
financial profitability of cowpea. This highlights the strong
influence of environmental and management conditions on
yield and profitability of cowpea cultivated under the
edaphoclimatic conditions of the northeastern semi-arid
region. The use of irrigation is a technology that acts
positively in maximizing these results.
y = -40.74x + 3069.1
R² = 0.91*
0
500
1000
1500
2000
2500
3000
3500
0 10 20 30 40 50 60 70
Yield (kg.ha-1)
Water stress (days)
A.
y = -16.018x + 1326.5
R² = 0.53*
0
500
1000
1500
2000
0 10 20 30 40 50 60 70
Yield (kg.ha-1)
Water stress (days)
E.
y = -135.06x + 10429
R² = 0.86*
0
2000
4000
6000
8000
10000
12000
14000
0 10 20 30 40 50 60 70
Biomass (kg.ha-1)
Water stress (days)
B.
y = -45.897x + 4892.1
R² = 0.78*
0
1000
2000
3000
4000
5000
6000
0 10 20 30 40 50 60 70
Biomass (kg.ha-1)
Water stress (days)
F.
y = -0.1169x + 32.283
R² = 0.34ns
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70
Harvest index (%)
Water stress (days)
C.
y = -0.099x + 32.237
R² = 0.39ns
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70
Harvest index (%)
Water stress (days)
G.
y = -0.0872x + 6.9734
R² = 0.83*
0
1
2
3
4
5
6
7
8
0 10 20 30 40 50 60 70
WUE (kg.ha-1.mm-1)
Water stress (days)
D. y = 0.267x + 2.1826
R² = 0.86*
0
5
10
15
20
25
0 10 20 30 40 50 60 70
WUE (kg.ha-1.mm-1)
Water stress (days)
H.
Ferreira; Silva
Nativa, Sinop, v. 10, n. 4, p. 577-584, 2022.
581
Table 1. Economic viability indicators of cowpea as a function of water stress in two cropping seasons in Campina Grande-PB.
Tabela 1. Indicadores de viabilidade econômica do feijão caupi em função do estresse hídrico, em duas épocas de cultivo, em Campina Grande.
Treatment
Season Y (kg ha-1) TC (R$) Economic viability indicators
GR (R$) NR (R$) RR (R$) PM (%)
T1
R 2633 1998.9 8897.9 6899.0 4.5 77.5
D 1763 1773.4 9006.4 7233.0 5.1 80.3
T2
R 2998 1948.9 10131.6 8182.7 5.2 80.8
D 1440 1723.4 7358.4 5635.1 4.3 76.6
T3
R 2780 1848.9 9396.4 7547.5 5.1 80.3
D 1038 1623.4 5301.6 3678.3 3.3 69.4
T4
R 2760 1698.9 9328.8 7629.9 5.5 81.8
D 438 1473.4 2235.6 762.3 1.5 34.1
T5
R 710 1498.9 2399.8 900.9 1.6 37.5
D 385 1273.4 1967.4 694.0 1.5 35.3
GR - gross revenue; NR - net revenue; RR - rate of return; PM - profit margin; TC - total cost; T1 - full irrigation; T2 - 5-day water stress; T3 - 10-day water
stress; T4 - 15-day water stress; T5 - rainfed cultivation; R - rainy; D - dry.
Figure 3. Gross revenue, net revenue, rate of return, profit margin for cowpea grown under water stress in rainy season (A, B, C and D) and
in dry season (E, F, G and H), respectively. R²- coefficient of determination; *significant by F test at 5% probability level.
Figura 3. Renda bruta, renda líquida, taxa de retorno, margem de lucro para o feijão caupi cultivado sob estresse hídrico em período chuvoso
(A, B, C e D) e em período seco (E, F, G e H), respectivamente. R²- coeficiente de determinação; *significativo pelo teste F a 5% de
probabilidade.
y = -137.87x + 10375
R² = 0.91*
0
2000
4000
6000
8000
10000
12000
0 10 20 30 40 50 60 70
Gross revenue (R$)
Water stress (days)
A.
y = -81.854x + 6778.2
R² = 0.54*
0
2000
4000
6000
8000
10000
12000
0 10 20 30 40 50 60 70
Gross revenue (R$)
Water stress (days)
E.
y = -137.7x + 8600.1
R² = 0.91*
0
2000
4000
6000
8000
10000
0 10 20 30 40 50 60 70
Net revenue (R$)
Water stress (days)
B.
y = -70.335x + 5039.1
R² = 0.47*
0
2000
4000
6000
8000
10000
0 10 20 30 40 50 60 70
Net revenue (R$)
Water stress (days)
F.
y = -0.0776x + 5.5996
R² = 0.91*
0
1
2
3
4
5
6
0 10 20 30 40 50 60 70
Rate of return (R$)
Water stress (days)
C.
y = -0.0335x + 3.8879
R² = 0.37*
0
1
2
3
4
5
6
0 10 20 30 40 50 60 70
Rate of return (R$)
Water stress (days)
G.
y = -1.2699x + 89.294
R² = 0.92*
0
20
40
60
80
100
0 10 20 30 40 50 60 70
Profit margin (%)
Water stress (days)
D.
y = -0.3503x + 69.045
R² = 0.25*
0
20
40
60
80
100
0 10 20 30 40 50 60 70
Profit margin (%)
Water stress (days)
H.
Water demand and technical-economic viability of cowpea grown in different production scenarios
Nativa, Sinop, v. 10, n. 4, p. 577-584, 2022.
582
4. DISCUSSION
In stages I and II, crop water demand showed very similar
values in both cropping seasons, and in stages III and IV,
crop water demand was higher in the dry season. This
occurred due to the climatic conditions observed in the
experiments, since at the beginning of the crop cycle, ETo
showed high values in both cropping seasons, but at the end
of the cycle its values were lower in the rainy season.
However, the range of variation in ETo values is considered
normal for these times of the year in the city of Campina
Grande-PB, since the condition of reduced cloudiness
remains during the dry season, which favors the increase of
temperatures and global solar radiation, with a direct effect
on ETo estimate (HENRIQUE; DANTAS, 2007; JÚNIOR
et al., 2018).
The Kc values obtained for cowpea cv. ‘Costela de vaca’
cultivated under the edaphoclimatic conditions of the Agreste
region of Paraíba, in the municipality of Campina Grande,
PB, were higher in the dry season (Table 1). These Kc values
were strongly influenced by soil water content during crop
development and by the evaporative demand of the region,
since the total rainfall was 205.9 mm in the rainy season and
only 19 mm in the dry season. Thus, the Kc values of cowpea
found in this study were not compatible with those suggested
by FAO-56 Bulletin (ALLEN et al., 1998). Nevertheless, they
were very close to the values obtained by Souza et al. (2015)
and Silva et al. (2016), who also determined these values
under climatic conditions similar to those of this experiment.
Significant decreasing linear responses were observed in
all agronomic parameters evaluated, except for water use
efficiency in the dry season. This indicates that, regardless of
cropping season, cowpea is negatively influenced by water
stress. Only the variable referring to the harvest index
showed no statistical difference, which points to its
insensitivity to the effects of the cropping season and water
stress. Water use efficiency in the dry season showed a
different response from the expected, because there were
reductions in all irrigated treatments, but for the rainfed
treatment, its value was very high, hence proving the
resistance of cowpea to water stress, which was able to
complete its cycle and obtain yield even with minimal water.
Ezin et al. (2021), evaluating the effect of water stress on
the agronomic traits of cowpea, also concluded that they
were significantly affected mainly when water stress occurred
at the beginning of flowering, which negatively affected pod
filling, consequently resulting in yield reductions. However,
Silva et al. (2021) observed that heirloom cultivars of cowpea
responded negatively to water stress, but maintaining pod
length and number of seeds per pod. These studies
corroborate the results obtained here, proving the
production efficiency of the heirloom cowpea cultivar
‘Costela de vaca’ even when subjected to water stress in its
reproductive stage, causing it to be widely cultivated under
family farming regime in the northeastern semi-arid region.
Cowpea yield was influenced by water restriction,
regardless of the cropping season, with higher yields in all
treatments in the rainy season. Under full irrigation
conditions, in the rainy season the maximum yield of cowpea
(2998 kg ha-1) was observed in the treatment that received a
five-day water suspension, while in the dry season, the
maximum yield was 1763 kg ha-1. Due to the great climatic
variability in the northeastern semi-arid region, the adoption
of techniques that enhance the increase of crop yield is of
fundamental importance, such as the use of varieties that are
more resistant to drought and mulching (Lopes et al., 2019).
The lowest yields were observed in rainfed cultivation,
with values of 710 and 385 kg ha-1, for the rainy and dry
seasons, respectively. The reduction of yield under rainfed
conditions was 73% for the rainy season and 78% for the dry
season, thus evidencing the importance of using irrigation to
increase crop yield. The average national yield of cowpea
under rainfed regime in the 2020/2021 season was 494 kg ha-
1 (CONAB, 2021).
Silva; Neves (2011), evaluating different cowpea cultivars
under rainfed and irrigated regimes, obtained average yield
values around 700 kg ha-1 and above 1000 kg ha-1,
respectively. Santos; Lima (2015) and Souza et al. (2020)
obtained yields above 1500 kg ha-1 under rainfed regime for
the heirloom cowpea cv. ‘Costela de vaca’; however, in the
study regions, the rainfall totals during the crop cycle were
higher than 350 mm. The interaction of cowpea performance
in irrigated and rainfed cultivation systems suggests a strong
influence of environmental factors on its yield, making it
dependent on environmental variations and management
(SILVA et al., 2017).
However, De Brito et al. (2016) evaluating the yield and
use of water in the cultivation of common bean under
different types of mulch and subjected to water restriction,
found that mulching did not contribute to minimizing the
negative effect of water restrictions on crop yield and water
use efficiency. Nhanombe (2019), evaluating the effects of
water restriction on common bean cultivated in no-tillage and
conventional systems, found that cultivation in no-tillage
system promoted water saving of 60 mm ha-1 and increased
WUE by 34.48%.
Cowpea has good water use efficiency, which enables its
cultivation in different cropping seasons; however, the basic
costs of production, depending on environmental conditions,
such as the action of water stress and agricultural practices
used in its cultivation, such as no-tillage and mulching, in
addition to the use of cultivars adapted to local climatic
conditions and acceptance by producers, directly contribute
to the economic viability of cowpea.
The economic viability indicators for cowpea cultivation
(Table 1) indicate that cowpea can be produced in Campina
Grande-PB in the rainy and dry seasons, provided that the
water restriction during the flowering and grain filling stages
does not exceed 10 consecutive days and its cultivation is
carried out under irrigated regime. The profit margin with the
use of full irrigation throughout the crop cycle was 77.5% and
80.3% for cowpea cultivation in the rainy and dry seasons,
respectively. As the price difference of the kilo of cowpea
paid to the producer between the cropping seasons was R$
1.73, it is more profitable for the producer to grow it in the
dry season. On the other hand, the rainfed cultivation,
despite having shown lower yield, is still profitable.
Silva et al. (2016), analyzing the economic viability of
cowpea grown under irrigation and rainfed regime, obtained
economic efficiency values of 80% and 70%, respectively.
The authors suggested that the effective operating cost can
be reduced with the use of labor from family farming.
The total production costs (Table 1) were higher in the
rainy season because, in addition to irrigation, there were
occurrences of rainfall, resulting in a higher growth of
spontaneous plants (weeds), consequently, a greater number
Ferreira; Silva
Nativa, Sinop, v. 10, n. 4, p. 577-584, 2022.
583
of weeding operations was necessary for their control.
Nevertheless, as the planting system was no-tillage and
irrigation was localized, spontaneous plants were suppressed
and did not interfere in cowpea yield.
One of the main factors that interfere in cowpea yield is
weed growth, and yield can be reduced by up to 73.5% when
weeds grow in the area throughout the crop cycle
(LACERDA et al., 2020). One of the solutions for weed
suppression in cowpea cultivation in both irrigated and
rainfed regimes is the use of mulch (JÚNIOR et al., 2019;
PEREIRA et al., 2020).
5. CONCLUSIONS
There was a greater water requirement by cowpea
cultivated in the dry season, so the Kc values found in this
period were higher than those obtained in the rainy season.
The agricultural practices of no-tillage and mulching
promoted higher yields of cowpea, although its cultivation
was influenced by the climatic conditions of the cropping
seasons and water stress. Nevertheless, cowpea showed
positive results of economic viability in both cropping
seasons, provided that the water stress does not last more
than 10 days during its reproductive stage. These results will
allow farmers to plan more efficiently cowpea production in
its different cropping seasons, in order to maximize crop
yield, consequently increasing its economic results.
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