Adaptability study of cowpea (Vigna unguiculata) genotypes for their agronomic performance and nutritive value in Adola district of East Guji zone of Oromia

The study was conducted to identify adaptable, high biomass and seed yield of Cowpea genotypes. Three Cowpea genotypes Bole, 6786 and 2351 were tested in a randomized complete block design (RCBD) with three replications. The result revealed that days to 50% flowering, days to seed maturity, plant height and seed yield was significantly (P<0.05) different among treatments. Among the tested genotypes late matured was obtained from genotype 6786 (131) days while late genotype was obtained from 2351 (113 days). The highest value of plant height was measured from genotype 6786 (132.8 cm), whereas the short plant height was obtained from genotype 2351 (64.8 cm). The highest seed yield was produced from Bole genotype (24.18 qt/ha), whereas the lowest seed yield was obtained from genotype 6786 (6.8 qt/ha). Chemical composition indicated genotype 2351 was the highest in total ash (TASH) and neutral detergent fiber (NDF) whereas less in crude protein (CP) genotype 6786 was the highest in crude protein (CP) while Bole variety had the highest in dry matter (DM), acid detergent lignin (ADL), acid detergent fiber (ADF) and organic matter (OM). This study implied that 6786 genotypes were well adapted and productive regarding the plant height (131.8 cm) and biomass yield (4.4 t/ha), which is hopeful to fill the low quantity ruminant feed gap. Besides, the nutritional values were promising, particularly the crude protein (CP) in 6786 genotypes. Thus it could be possible to conclude that cowpea genotype, especially 6786 used as a protein supplement. Based on its adaptability, high biomass, plant height, good CP content 6786 genotype is recommended for further promotion in the midland of East Guji zone and similar agro-ecologies.


I. Introduction
Feed shortage in quantity and quality remains the leading constraint to good animal performance in Ethiopia (Yayneshet et al., 2009). Natural pasture and crop residues are the main feed sources (feedstuffs). Feedstuffs of such composition are insufficient to provide year round supply of adequate quantity and quality of nutrients beyond maintenance (Hindrichsen et al., 2001). Legumes are the most important forage plants that substantially improve livestock feed as they can provide the essential protein for animals, improving soil fertility, food crop production, and household nutrition through a more reliable supply of milk and meat (Akinlade et al., 2005;Alemayehu, 1997). Cowpea (Vigna unguiculata (L.) is a leguminous crop grown throughout West Africa, often in association with pearl millet (Pennisetum glaucum L.) and sorghum (Sorghum bicolor L.). Cowpea is well adapted to the harsh growing conditions, including low soil fertility, high temperatures, and drought (Turk et al., 1980). Cowpea can fix nitrogen to improve soil fertility and cropping system productivity. Additionally, farmers feed cowpea fodder to livestock to increase income and collect the manure produced for use in their fields, thereby reduces farmers' reliance on commercial fertilizers and sustain soil fertility (Odion, et al. 2007;Akinlade, et al., 2005). Previous studies with cowpea (Gwanzura et al., 2012;Akinlade et al., 2005;Ebro et al., 2004;Alemayehu, 1997) indicated this legume improves soil fertility and enhances the intake and utilization of poor quality roughage, consequently improves livestock production and productivity. Another important feature of cowpea is its ability to suppress weeds, particularly Striga species (Dawit et al., 2009). Therefore, this experiment was conducted to evaluate and identify adaptive, high quality yielding cowpea genotypes in the midland of Guji east Guji zone.

Description of the study area
The experiment was carried out at Adola sub-site of Bore Agricultural Research Center, Adola district, Guji Zone of Oromia. Adola district is located around 470 km from Addis Ababa and 120 km from the zonal capital city, Negele Borena. It is an area where a mixed farming and sami-nomadic economic activity occurs, which is the local people's major livelihood. The total area of the district is 1254.56km 2. The district is situated at 5 o 44'10" -6 o 12'38" N latitudes and 38 o 45'10" -39 o 12'37" E longitudes. The district is characterized by three agro-climatic zones, namely highland 11%, mid-land 29% and low-land 60%, respectively. The district's major soil type is nitosols (red basaltic soils) and orthic Acrosols (Yazachew and Kasahun, 2011).

Experimental treatments and design
The study was executed using Bole, 6786 and 2351 genotypes. The experiment was conducted in a randomized complete block design with three replications. Seeds were sown in rows at a spacing of 30 cm with seed rate of 30 kg ha -1 . Plot size of 1.8 m x 3 was used. NPS fertilizer at 100 kg ha -1 was uniformly applied for all treatments at sowing time

Data collection methods
Relevant data including days 50% flowering, days to seed maturity, plant height, seed yield and nutritive value were collected. Seed yield weight was calculated at 10% moisture content. Seed yield weight was calculated at 10% moisture content. At 50% flowering stage, each plot's middle rows were harvested for dry matter herbage determination and chemical analysis. Plants were harvested at ground level and fresh biomass weighed immediately using a 0.1 g scale. A sub-sample of 15-20% of the total weight was separated and put into a paper bag for dry matter herbage determination. The samples were oven-dried at 105 0 C for 24 hours. To determine grain yield the pods were harvested from the rest rows at optimum physiological maturity by hand picking.

Statistical analysis
All collected data were analyzed using a general linear model procedure SAS (SAS, 2002) version 9.1. Means were separated with least significant difference (LSD) at 5% significant level. The statistical model for the analysis data was: Yijk= µ + Aj + Bi + eijk

Where
Yijk= response of variable under examination; µ = overall mean; Aj = the jth factor effect of treatment/ cultivar; Bi = the ith factor effect of block/ replication, eijk = the random error.
Published with open access at journalbinet.com. © 2020 The Authors, Research Paper.  (2014), possibly due to ecological and genetic differences.

III. Results and Discussion
Early matured genotype was 2351 (113 days) followed by Bole genotypes (127.9 days) while late matured genotypes were obtained from 6786 (131 days) to set seed when compared to rest genotypes. Early maturity is a relatively important agronomic characteristic measured by such criteria as days to flowering or days to maturity (Singh and Rachie, 1985). Our results for days 50% flowering and maturity were highly higher than reported by Cobbinah et al. (2011), who found average results of 39.5 and 51.6 days to reach 50% flowering and maturity for cowpea genotypes in Ghana, respectively.
The result of the current study for days to 50% flowering was higher than reported by Agza et al.
(2012) and Rao and Shahid (2011), who found average results of 63 and 63.7 days, respectively, possibly due to ecological and genetic differences.
The highest plant height was measured from genotype 6786 (132.8 cm) followed by Bole genotype (66.8 cm) whereas the short plant height was obtained from genotype 2351 (64.8 cm). The highest seed yield was produced from Bole genotype (24.18 qt/ha) followed by genotype 2351 (19 qt/ha) while the lowest seed yield was obtained from genotype 6786 (6.8 qt/ha). Non-significant differences to biomass yield, pod per plant, and seed yield were observed between treatments (P > 0.05). However, numerically had high yield was recorded among treatments. The highest biomass yield was produced from genotype 2351 (5.9 ton/ha), followed by genotype 6786 (4.4 ton/ha) while the low biomass yield was obtained from Bole variety (3.7 ton/ha). The highest pod per plant produced from genotype 6786 (12.7) followed by genotype 2351 (10.2) whereas the lowest pod per plant was obtained from Bole genotype (9.11). The highest pod length was obtained from 6786 genotypes (3.27 cm) followed by Bole genotype (2.9 cm) while the short pod length was obtained from genotype 2351 (1.7 cm) and also expressed in Figure 01.

Chemical Composition
The chemical composition indicated that DM, CP, NDF, ADL, ADF, TASH and OM was not significantly (P>0.05) different among treatments. However, numerically had high yield was recorded among treatments. Genotype 2351 was highest in TASH and NDF while less in CP, genotype 6786 was highest in CP whereas less in DM, NDF, ADL and OM, Bole variety had the high in DM, ADL, ADF and OM while less in TASH compared the rest treatments. The minimum CP content in the ruminant diet should be around 6.0 -8.0% of dry matter for adequate rumen microorganism activity (Van Soest, 1994), suggesting that hay CP content in investigated cowpeas are more than twice needed rations. Based on its CP% content, Gwanzura et al. (2012) suggested that cowpea has the potential of being utilized as protein supplement for ruminants on low quality roughages.

IV. Conclusion
This study indicated that genotype 6786 was well adapted and productive regarding the plant height (131.8 cm) and biomass yield (4.4 t/ha), which is hopeful to fill the low quantity ruminant feed gap supply the community. The nutritional values were promising the crude protein (CP) content in genotype 6786, particularly. Thus it could be possible to conclude that the cowpea genotype 6786 was used as a protein supplement for the midland of East Guji. Based upon its adaptability, high biomass plant height and good CP of genotype 6786 are recommended further promotion in the midland of East Guji zone and similar agroecology.