Distribuição de fósforo no solo em razão do sistema de cultivo e manejo da adubação fosfatada

Abstract

Cropping systems and management of phosphate fertilization affect P availability in the soil, its accessibility for plants and finally, crop yields. This calls for an evaluation of P distribution in the soil profile, in long-term experiments, to understand the impact of each cropping system and fertilization management on this process. An area of Embrapa Cerrados, in Planaltina - DF, in an Oxisol, with very low P content at the beginning of the experiment, was cultivated for 14 years with soybean and corn in the summer and millet as winter cover crop in the last six seasons; fertilization consisted of 80 kg ha -1 yr -1 of P 2O 5, as triple superphosphate or phosphate rock, applied in seed furrows or broadcast, in conventional tillage (CT) or no-tillage (NT). Phosphorus distribution was evaluated in seven soil layers (0- 2.5 cm, 2.5-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, 30-40 cm, and 40-50 cm) using the extractor Bray 1. In the 14 th year of cultivation, the soybean yield data were used. The results were statistically analyzed to compare P distribution in the soil profile and the yield. The distribution of soil-extractable P after 14 years of cultivation was influenced by the source and application form of phosphate fertilizer down to a depth of 10 cm in NT and to 20 cm in CT. Under CT, there was a slight depth gradient, while under NT there was a strong gradient, primarily for broadcast applications. Highest P levels were found in the 0-2.5 cm layer, for both application forms. P contents were higher down to 10 cm, but in the 10-20 cm layer contents were lower than in CT. Despite the management effect of phosphorus fertilization on soil P distribution, soybean grain yield in the 14th year was affected by the cropping system only, and the soil under NT produced 15.5 % more grain than the CT.