High soil phosphorus application significantly increased grain yield, phosphorus content but not zinc content of cowpea grains

Abstract Background and aims Phosphorus (P) is limiting in many soils of cowpea producing areas. To ameliorate the impact of soil P deficiency, the use of P-based fertilizers is highly recommended. However, a negative association between zinc (Zn) content and high P application has been reported in some crops. There are few reports about P-Zn interaction on cowpea. Thus, in this study, the response of cowpea to the varying amounts of P and their effect on plant P and Zn content, and yield were investigated.Methods Thirty genotypes were grown at three P rates in screenhouse and field environments. In the screenhouse, shoot biomass, P and Zn content were measured at 55 days after sowing. In the field, grain yield, P, and Zn content were determined in the harvested tissues when plants reached full maturity.Results Higher rates of P in the growth media led to significantly increased shoot biomass, and grain yield but were not associated with a significant change in shoot or grain Zn content. There was not a significant correlation between grain yield and Zn content in high soil P (p < 0.05). The site regression analysis revealed that the first two principal components explained 69.76%, and 22.30% of total variance for grain yield, and 69.01% & 24.66% of total variance for Zn content.Conclusions The effect of higher P application on reduced shoot and grain Zn content may be genotype-dependent and could be circumvented if genotypes with high Zn content under higher P supply are identified and cultivated.