Iron and zinc levels in Vigna unguiculata (L.) Walp under varying phosphorus and fixed nitrogen treatment conditions

Abstract

AbstractUsing phosphate fertilizer (particularly at high levels) to improve the phosphorus (P) level of soils during the cultivation of legumes and other cereals unfortunately has negative effect on the levels of micronutrients like zinc (Zn) in grains. This study evaluated the influence of P and nitrogen (N) fertilization on iron (Fe) and Zn levels of cowpea grains. Cowpea genotypes B301, TVu 16514, IT90K‐205‐8, UAM09‐1046‐6‐1 and TVu 1272 were grown in greenhouse pots containing barren soils (to simulate micronutrient‐deficient soils) in two stages of varied P (0, 20, 40, and 60 kg P ha−1) with and without N (i.e. P only and P v N). The effect of these interactions on Fe and Zn levels were measured. Application of P alone showed no significant (p > 0.05) negative influence on Zn and Fe content of the grains. However, a combination of N and P fertilization reduced Zn content significantly at 60P (p < 0.05). Further evaluation showed TVu 1272 as highest in terms of Fe and Zn at all P levels. Significant reduction of grain Zn was found at 60P on N and P interaction. No such negative correlation was observed for Fe. TVu 1272 (a high‐yielding genotype) is recommended as a source of high micronutrient.