Understanding the Nexus of Genotype, Root Nodulation, and Soil Nutrients for Shoot Biomass Production and Seed Yield in Cowpea (Vigna unguiculata L. Walp)

To enhance the productivity of cowpea for seeds and shoot biomass yields, the complex interwoven relationships of genotype, soil nutrients, and nodulation were studied. A 4-year field study was conducted with ten cowpea accessions in a randomized complete block design of three replicates and data collected on soil parameters, root nodulation, plant growth, and yield characters were analyzed for variance components and correlation analysis. Genotype and year influenced the rate of nodulation, plant nutrient uptake, shoot biomass, and seed yield. Nodulation and nitrogen uptake increased shoot biomass production but not seed yield. Early maturity was associated with high seed yield, while late maturity enhanced biomass production. Cowpeas differ significantly in nodulation efficiency and soil nutrient utilization for seed yield and biomass production, with IT98K-205–8 being the most efficient. Soils cultivated for cowpea showed reduction in clay content and soil nutrients, but increased in silt content, soil acidity, and phosphorus uptake. Proportion of phosphorus uptake was significantly higher than nitrogen and organic carbon uptakes in cowpea. Increasing uptake of nitrogen and organic carbon is inversely associated to nodulation, growth parameters, and shoot biomass, while phosphorus uptake is directly correlated with seed yield. IT89KD-288 and IT00K-1263 were superior for nodulation and shoot biomass production (> 28 tons ha−1), while IT08K-150–12 and IT00K-1263 were best for seed yield of > 2.0 tons ha−1. This study reported the efficiency of root nodulation of native rhizobia and nutrient utilization as among the important elements required for optimum development and yield of cowpea. IT00K-1263 that combines high biomass with seed yield is a candidate for dual-purpose, while IT08K-150–12 could be useful as an early-maturing high-yield variety. Inherent nutrient utilization efficiency of IT98K-205–8 could be explored in future improvement programs.