ABSTRACT
Cowpea (Vigna unguiculata L.) is one of the most important grain legumes in the semi-arid regions of many African countries including Ethiopia. However, it is less cultivated and scarcely distributed pulse crop in Abergelle due to a lack of improved varieties. A field experiment was conducted during the 2014 and 2015 main cropping seasons using a randomized complete block design with three replications to evaluate seven cowpea varieties for yield and yield related traits under rain-fed conditions at Abergelle Agricultural Research Center on station. Analysis of variance of data showed significantly varietal differences at P< 0.05 for days to 50% flowering; pod filling period, 90% physiological maturity, pod length and plant height, number of seeds per pod, seed yield, grain yield, biomass yield and thousand seed weight. However, no significant varietal difference was observed for harvest index. Bekur had the highest seed yield (14.85 qt.ha-1) followed by Bole (13.57 qt.ha-1), while the lowest seed yield was observed from BEB (6.71 qt.ha-1). Overall, Bekur and Bole had better performance compared to the other varieties for yield and the yield related traits. As compared to the rest, these two varieties were therefore recommended as promising varieties to the farmers of Abergelle area and other districts having the same agro-ecologies based on their optimal performance for adoption.
Key words: Optimal performance, yield, yield related traits, Vigna unguiculata L.
Cowpea (Vigna unguiculata L. Walp) is a leguminous plant belonging to the Fabaceae family. It is an important grain legume in drier regions and marginal areas of the tropics and sub-tropics. The grains are good source of human protein, while the haulms are valuable source of livestock protein (Dereje et al., 1995; Fatokum, 2002). It is the second most important food grain legume crop in tropical Africa, next to Phaseolus vulgaris, the common bean (Arnon, 1972). Nigeria, Niger, Burkina Faso, Uganda and Senegal grow cowpeas for the market, but they are widely grown as a subsistence crop for human use in nearly all sub-Sahara African countries.
Cowpea is a warm-weather crop with somewhat higher temperature requirement than maize. Cowpea is drought tolerant annual crop in condition where moisture deficiency has less effect on seed formation. It grows with less rainfall and under more adverse condition than haricot bean. Like other leguminous crops, it is also grown for improving soil fertility (Tesema and Eshetayehu, 2003). Cowpea withstands heat better than most other legumes do. Cowpea can be grown in a wide variety of soils, but yields better on well-drained soils with medium fertility (Arnon, 1972).
Cowpea is a principal food legume in many African countries including Ethiopia, where tender leaves, fresh pods and grains are consumed. In Ethiopia, cowpea seed is mostly used in the form of food dishes ‘nifro’, ‘shiro’ etc. Cowpea provides feed, forage, hay, and silage for livestock, and green manure or maintaining the productivity of soils. When intercropped with cereals, it compensates for the loss of nitrogen absorbed by cereals through nitrogen fixation. It is also a good cover crop that limits soil erosion (Onwueme and Sinha, 1991).
Early maturity and moderate degree of drought tolerance led the crop’s vital role in farmers’ strategies for risk aversion in drought prone lowland areas of the country (Fikru, 2007). However, yield per unit area is very low especially in Abergelle, Northern Ethiopia. The major constraints that limit the production of cowpea are low productivity of the crop at the farmer’s level, moisture stress, absence of improved high yielding varieties, low soil fertility, losses due to insect pests and disease. Hence, this study was intended to select the best performing and suitable improved variety/varieties of cowpea for their yielding ability in the moisture stressed areas of Abergelle district.
Description of the study area
The field experiment was carried out under rain-fed conditions at Abergelle Agricultural Research Center on station during the 2014 and 2015 main cropping seasons. Abergelle is located in the central zone of Tigray region at about of 903 km north of Addis Ababa and 120 km south west of 'Mekelle' and situated at 13°14’06”N latitude and 38°58’50”E longitude. The area is agro-ecologically characterized as hot warm sub-moist lowland (SMl-4b) located at an altitude of 1450 masl. Plains, hills and river valley, characterize the topography of the district and it is highly exposed to soil erosion. Most soils of the district are dominated by sandy textured with poor water holding capacity and less fertile hence most crops failed to produce good yield (Dereje et al., 2007).
The dominant soil types of the study area are fine-grained ones called ‘walka’, ‘bahkel’, ‘hutsa’, and ‘mekayih’. The average annual rainfall varies from 350 to 650 mm and the temperature ranges from 18 to 42°C. The distribution of rainfall is erratic and variable, which results in strong variation in crop yields (Dereje et al., 2007). The rainfall distribution is unimodal, concentrated during the summer (July to August) leading to one cropping season per year (Belay and Meresa, 2017).
Experimental design and crop management
Six cowpea varieties, sourced from Melkasa Agricultural Research Center (MARC) and one local check from Abergelle area, were evaluated in this study (Table 1).
These varieties were planted under field conditions in a randomized complete block design (RCBD) replicated thrice. The plot size was 4 × 3.2 m (12.8 m2) having 8 rows with harvestable plot area of 1.6 × 4 m (6.4 m2) with four rows and spacing 40 cm between rows and 10 cm between plants was maintained. The spacing between replication, blocks and plots within each block was 1.50, 1 and 0.50 m, respectively. Di-ammonium phosphate (DAP) fertilizer was applied at a rate of 100 kg ha-1 at planting. Livestock were excluded by fencing. No irrigation was applied. Weeds were controlled periodically by hand weeding and other management practices like pest or disease-control was done as required.
Data collection and sampling techniques
Phenological data such as days to flowering, pod filling period and days to maturity; growth traits (plant height and pod length) were recorded. Days to flowering was recorded as the number of days form emergence to when 50% of the plants had flowered in a plot. Seed filling period was recorded as days from flowering to maturity. Days to 90% maturity is the number of days from emergence to the stage when 90% of the plants in a plot have reached physiological maturity. At pod setting stage five plants were randomly selected from each plot and carefully tagged. These plants were used to measure traits like plant height and pod length. Data were also collected on seed yield and yield related traits such as number of pods per plant, number of seeds per pod, 1000 seed weight, grain yield, biomass yield and harvest index. The four central rows of each plot were harvested for grain yield. Five plants were randomly selected from the four central rows to determine the yield related traits, which consisted of number of pods per plant, number of seeds per pod. Number of pods per plant was determined by counting pods of the five randomly selected plants averaged. To determine the number of seeds per pod, total number of seeds in a pod was counted on five randomly sampled pods taken from the five randomly selected plants average for each. Thousand seed weight was recorded as the weight of one thousand seeds randomly picked and weighted. Seed yield: central four rows were threshed from each plot and seeds obtained from them was adjusted to standard moisture level (10%) per plot in grams and converted into quintal per hectare. Biomass yield: The weight in grams of sun dried above ground parts of the plants was recorded from the central four rows. Harvest index: was calculated as the ratio of seed yield to total above ground biomass yield (biological yield).
Data analysis
The collected data was subjected to combined analysis of variance (ANOVA) using the Statistical Analysis System (SAS) software version 9.1 program (SAS Institute, 2004). Means were separated using Fisher’s Least Significant Difference (LSD) test at 5% level of probability as stated in Gomez and Gomez (1984).
Phenological and growth traits
The combined analysis of variance showed that varieties performed significantly differently for all the phenological and growth traits (days to 50% flowering, pod filling period, 50% maturity, plant height and pod length (Table 2).
Yield and yield related traits
Significant (P≤0.05) varietal difference was observed for yield and all yield related traits except harvest index (Table 3). The current variations in yield and yield related traits among varieties consent with previous reports of Daniel et al. (2014) and Teame et al. (2017) in common bean, Tekle (2014) in cowpea. The results from the analysis of variance for number of seeds per pod and thousand seed weight showed very highly significant (P<0.001) difference (Table 4). The number of seeds per pod ranged 10 to 14. The highest number of seeds per pod was obtained from Bekur followed by Kenkenty, while the lowest number of seeds per pod was obtained at BEB. However, the highest thousand seed weight was recorded from BEB variety (130 g) followed by Bole (118) and the lowest thousand seed weight recorded from local cultivar (67 g). Bekur and Bole had the highest seed yield of 14.85 and 13.57 qt.ha-1, respectively, while BEB had the lowest yield of 6.71 qt.ha-1. Finally, the highest biomass yield was observed in Bole (33.93 qt.ha-1) followed by Bekur (32.72 qt.ha-1), whereas the lowest biomass yield was recorded from BEB (17.97 qt.ha-1).
Based on the result from the present study, cowpea yield in the study area is low. The adoption of early maturing varieties, as done in this study, can help in minimizing this problem. Early maturing varieties have been shown to yield better than the late maturing varieties. Besides, they are more suitable to areas with unreliable rainfall in terms of total amount, distribution and duration where crop failure is often attributed to early cessation of rains and thereby making it adaptive to different agro ecological environments.
Analysis of variance of data showed significant varietal differences at P≤0.05 for days to 50% flowering; pod filling period, 90% maturity, and plant height, number of seeds per pod, grain yield, biomass yield and thousand seed weight. However, no significant varietal difference was observed for harvest index. The combined analysis result indicated that the early maturing cowpea varieties Bekur and Bole had the highest yield of 14.85 and 13.57 qt.ha-1 respectively. The earliness traits (days to flowering, seed filling period and days to physiological maturity) enables them to flower, pod fill and mature early, therefore escaping from moisture stress, the most important drought factors that results in reduced yield. As compared to the others, Bekur and Bole were therefore recommended as promising varieties to the farmers of Abergelle area and other districts having the same agro-ecologies based on their optimal performance for adoption.
The authors have not declared any conflict of interests.
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