Productivity of wheat following non-fetilized soybean in a dystrophic Dusky Red Latosol

Abstract

This research evaluates the soil fertility potential for wheat of a dystrophic Dusky Red Latosol of the state of Paraná, Brazil, and the technical and economical yield response of wheat, double cropped wheat-soybean, as a function of phosphorus and potassium rates applied to wheat and/or soybean. The experiment was carried out at National Soybean Research Center/Embrapa, Londrina, PR, from 1990 to 1995. The treatments were six rates of P and K fertilization arranged in the following way: 1) no fertilization for both soybeans or wheat; 2) 30 kg/ha of K₂O for wheat; 3) 50 kg/ha of P₂O₅, for wheat; 4) 50 kg/ha of P₂O₅ and 30 kg/ha of K₂O for wheat; 5) 50 kg/ha of P₂O₅ and 30 kg/ha of K₂O for wheat, 30 kg/ha of P₂O₅ and 50 kg/ha of K₂O for soybeans; 6) 50 kg/ha of P₂O, and 30 kg/ha of K₂O, for wheat, 60 kg/ha of P₂O₅ and 100 kg/ha of K₂O for soybeans. Every year, the fertilizers were mechanically applied in the sowing furrow. The soil maintained its originally high fertility level during the three first years, even when no fertilizer was applied for soybeans. Application exclusively for wheat crop of 50 kg/ha of P₂O₅ was enough to maintain the P content in the soil above medium levels during the six years. When P and K contents in the soil approached the critical levels, the effect of the fertilization applied for soybeans was detected in the wheat crop. The net income from wheat crop fertilization became bigger as soil P and K contents dropped approaching the critical levels.