Fertilización fosfatada de los principales cultivos bajo siembra directa mecanizada en la región oriental del Paraguay Phosphorus fertilization in no-till mechanized farming of eastern Paraguay

No-till agriculture is increasing in Paraguay and it is necessary to adapt phosphorus fertilizer recommendations for this production system. The main objectives of this work were to determine the effect of P fertilization on wheat, corn and soybeans yields and to calibrate the soil test methodology for extracting P using the Mehlich-1 extractant. Four experiments were conducted in the Departments of Caaguazu and Amambay. The experimental design was a randomized block with split plots and three replications. Main plots were fertilized with 0, 50, 100, 200 and 400 kg P2O5 ha -1 to create P levels and wheat was planted. In the summer cycle, the subplots were fertilized with 0, 40, 80 and 120 kg P2O5 ha -1 , and planted with soybeans and corn. Crops responded to P application and the degree of response was inversely related to P concentration in the soil at a depth of 0-10 cm. The critical soil P level was 16 mg kg -1 in soils with