Atributos químicos do solo em função da adubação nitrogenada em sistemas agrossilvipastoril

Abstract

An agrosilvopastoral system presents benefits in the soil-plant-animal system, both for the producer and for society. The productive potential of agrosilvopastoral systems with the use of fertilizers in the soil must be well understood, especially nitrogen, including nitrogen deficiency in agrosilvopastoral systems can restrict productivity since these systems also have a high demand for this nutrient. In agricultural systems, applied nitrogen can contribute to changes in the chemical contents of the soil, and it is necessary to understand the dynamics of soil chemical elements as a function of nitrogen fertilization. Therefore, the objective of this study was to evaluate the variation of soil chemical attributes as a function of nitrogen fertilization in an agrosilvopastoral system, aiming at improving the efficient use of nitrogen. The experiment was carried out at the Technological Reference Unit of EMBRAPA Cocais and the State University of Maranhão in Pindaré Mirim, MA. The experimental area consisted of 3.6 ha established with pasture of Urochloa brizantha cv. Marandu, intercropped with corn Zea mays and eucalyptus Eucalyptus. The area was divided equally into three blocks, with four treatments: (1) Control, without nitrogen fertilization; (II) Application of 100 kg/ha of Nitrogen (N); (III) Application of 200 kg/ha of N; (IV) Application of 400 kg/ha of N. Soil samples were collected for chemical analysis in the laboratory. The EMBRAPA methodology was used to determine the chemical attributes. There were no statistically significant differences for the pH values ​​and P, H+Al and V% contents in relation to the different doses of nitrogen fertilization applied. There was a decrease in the Mg content of the most superficial layers (0-10 and 10-20 cm) to the depth of 20-30 cm with the increase in the N doses. For the potassium content, a reduction was observed in the soil as the N fertilization doses were increased. The values ​​of sum of bases (SB) and CTC showed a behavior similar to the soil bases in relation to the increase in the N doses applied to the soil, having a small decrease up to the dose with 200 N and subsequently an increase with the dose of 400 N. The application of high doses of N in the soil causes the leaching of magnesium from the superficial layers, as well as a decrease in potassium in the soil due to greater extraction by U. brizantha cv. Marandu. Higher doses of N can increase the calcium content in the soil by the absorption and cycling of nutrients in the soil. A longer evaluation period is necessary to confirm variations in soil chemical attributes due to increased nitrogen fertilization in agrosilvopastoral systems