SOYBEAN RESPONSE TO POTASSIUM AND PHOSPHORUS IN A PALEUDULT SOIL AT BALSAS, MA

With the expansion of soybeans to the low latitude region of Brazil, studies to establish new technologies for the crop are necessary since very little research has been done in that area. Usually recommendation for soil fertilization and liming are based on information adapted from other regions. With the objective of evaluate P and K fertilization, a field experiment was conducted during the 1984/85 and 1985/86 seasons, in the county of Balsas, MA, Brazil. The dosages of K were: 0, 40, 80 and 120 of K2O/ha(-1), in the first year, and 0, 50, 100 and 150 kg K2O/ha(-1) in the second year. P was applied at 0, 80, 160, 240 P2O5/ha(-1) in the first year and 0, 100, 200 and 300 kg of P2O5/ha(-1) in the second year, applied to the planting rows. The research was conducted in a Paleudult soil that had been cultivated with high land rice for two previously years, without fertilization or liming. Three tons/ha(-1) of lime and 10 kg of Zn/ha(-1) in addition to the inoculant applied to the seed (200 g/50 kg) were used. The results showed great response to P with maximum yield at dosages close to 200 kg of P2O5/ha(-1) and the economical dose of 150 kg/ha(-1) during the two years of study. For potassium, maximum yield was obtained with 50 kg of K2O/ha(-1), and the economic dose bellow zero.