Abstract
Cowpea is an important legume crop in Africa, valued highly for its grain and also haulms, which are a tradable commodity in fodder markets. Fodder market surveys in Northern Nigeria showed that groundnut haulms were priced higher than cowpea haulms, probably because of their superior nutritive value. The economic value of haulms has prompted cowpea breeders and livestock nutritionists to explore haulm fodder traits as additional selection and breeding criteria. Fifty cowpea genotypes cultivated across five locations in Nigeria in 2013 and 2014 were evaluated for food fodder traits. Significant (P < 0.05) genotypic dependent variations were observed in yields (kg/ha) of grains (537–1082) and haulms (1173–3368), though significant (P < 0.05) effects of location and year were observed. Grain and fodder yield had a tendency to be positively correlated (r = 0.26, P = 0.07). Haulms were analyzed for nitrogen (N), fiber fractions, in vitro digestibility, and metabolizable energy content. Highly significant variations were observed in all genotypic and livestock nutrition traits, although location and year had significant effects. Trade-offs between grain yield and haulm fodder quality traits were largely absent and haulm acid detergent lignin and grain yield were even inversely correlated (r = -0.28, P = 0.05), that is high grain yielders had decreased haulm lignin. However, haulm N and grain yield also tended to be negatively associated (r = -0.26, P = 0.07). Haulm fodder quality traits and haulm yield were mostly positively correlated (P < 0.05). Broad sense heritabilities for grain and fodder yield were 0.50 and 0.29, respectively, while heritability for haulm fodder quality traits ranged from 0.61 to 0.67, providing opportunities for concomitant increase in grain yield and haulm fodder quality traits. Selection of the 10 highest ranking genotypes for grain yield, haulm yield, haulm N, and haulm in vitro organic matter digestibility showed selection groups overlapping, suggesting that multi-trait selection is feasible. Economical evaluation showed that choice of primary traits is context specific, highlighting the need for identifying and targeting appropriate genotypes to fit different production systems. Considering haulm quantity and quality as traits of economic value can increase overall plant value in mixed crop-livestock systems.
Highlights
Legumes are important crops of mixed crop-livestock systems, providing highly nutritious food in their grains and highly palatable fodder in their haulms while at the same time contributing to soil fertility through nitrogen fixation (Alemayehu, 1997)
Haulm bundles were weighed and the samples were collected, dried, ground through 1 mm sieve and analyzed for fodder quality traits using near infrared spectroscopy (NIRS)
Cowpea haulms were sold in bundles of small size (3.8–5.5 kg), while groundnut haulms were sold in bundles of three sizes: small (5–6 kg), medium (11.5–12.5 kg), and large (16–18 kg)
Summary
Legumes are important crops of mixed crop-livestock systems, providing highly nutritious food in their grains and highly palatable fodder in their haulms while at the same time contributing to soil fertility through nitrogen fixation (Alemayehu, 1997). The need and scope for improving the productivity of cowpea in West Africa through breeding and management is urgent, with substantial potential impacts on food and fodder security and, livelihoods in the region. Cowpea haulms are already an important fodder source for livestock in crop-livestock systems in the Sahel regions of West Africa where feed scarcity and seasonality is the major constraint to improved livestock production (Agyemang, 2002). Ex ante assessments of the impact of cowpea varieties concomitantly improved for grain and haulm yield and haulm fodder quality suggested multiple benefits and high likely adoption rate of such varieties (Kristjanson et al, 2005). The present work explores: (1) lessons from legume haulm fodder trading; (2) genotypic variations in grain and haulm yield and haulm fodder quality traits in 50 genotypes of cowpea; (3) the stability of traits across years and locations; (4) trait relationships and tradeoffs; and (5) opportunities of multi-trait improvement of cowpea
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