Effect of phosphorus, potassium and magnesium fertilization on yam bean inoculated with Bradyrhizobium and growing in an alic latosol soil

In order to evaluate the effects of phosphorus, potassium and magnesium application on the nutrient absorption and yield of yam bean (Pachyrhizus erosus (L.) Urban), in a Yellow Latosol of the Zona da Mata of Pernambuco State, Brazil, an experiment was carried out using the strain of Bradyrhizobium sp. NFB 450, isolated from yam bean and selected for efficient N-2 fixation in previous experiments. Potassium and magnesium were applied in the proportion of 2:1 (K2O:MgO) in increasing levels (0:0, 40:20, 60:30 and 80:40 kg ha(-1) of K2O and MgO, respectively), and crescent levels of phosphorus (0, 20, 40, 60 and 80 kg ha(-1) of P2O5) were added in the form of triple superphosphate. Maximum dry matter production, total N and total P accumulated were obtained when applying 64 kg ha(-1) of P2O5. A significant effect of K2O:MgO levels was observed in relation to the treatment without K and Mg application; nevertheless, higher levels of K2O:MgO decreased dry matter and total N, and increased total P accumulation. Yam bean responded to low levels of P, K and Mg fertilizer, and showed ability in N-2 fixation, with great potential for biomass production.