COWPEA RESPONSE TO PHOSPHORUS AND ZINC

ABSTRACT Low grain yield of cowpea is influenced by several production factors, especially inadequate soil fertilization, in particular, phosphorus application. Tropical soils have low phosphorus and zinc levels due to either the source material or the absence of fertilization, which restricts cowpea grain yield; besides of that, zinc deficiency is accentuated with phosphor application. This study aimed to evaluate the effect of fertilization with phosphorus and zinc on cowpea yield. Two experiments were conducted, one with ‘BRS Guariba’ cultivar and another with ‘BRS Aracê’ cultivar. Both of them were performed on a medium-texture dystrophic Yellow Latosol (Oxisol), in the city of Magalhães de Almeida, Maranhão state (Brazil), in 2015. The experimental design was a randomized complete block in a 4 x 4 factorial scheme, using four doses of phosphorus (0, 40, 80, and 120 kg P2O5 ha-1), and four of zinc (0, 2, 4, and 6 kg of Zn ha-1). There was an interaction between these minerals (p<0.01). Maximum grain yields of 1,376 kg ha-1 and 2,165 kg ha-1 were obtained at doses of 118 kg P2O5 ha-1 and 0.9 kg zinc ha-1 for ‘BRS Guariba’, and 120 kg P2O5 ha-1 and 3.1 kg zinc ha-1 for ‘BRS Aracê’, respectively. The production component of greatest influence on grain yield was the number of pods per plant, with average values of 6 and 10 for ‘BRS Guariba’ and ‘BRS Aracê’ cultivars, respectively. The mean correlation coefficient was 0.82 (p < 0.01).