Aplicação de xisto retortado em sistema silvipastoril: impactos nos fluxos de nitrogênio e na composição química da solução do solo

Abstract

Integrated production systems, as Silvopastoral Systems (SSPs), can generates environmental and economic benefits for society, combining productivity and environmental conservation. Urea is the main source of nitrogen (N) used in Brazil, but this fertilizer has a low efficiency in nitrogen fertilization and can be lost in different ways. The combined use of the retorted shale (ROS) with urea may have a potential in reducing NH3 volatilization losses, thus improving the efficiency of N utilization. However, this potential needs to be carefully evaluated in order to get scientific support for this practice. The aim of this research was to investigate the feasibility of using ROS in the soil in reducing N losses from urea and the potential of contamination of soil, air and water in a silvopastoral system. Field experiment has been carried out in a silvopastoral system established in 2012, with experimental design of randomized blocks and split-plots, on an Acrisol. The main treatments consisted of spatial arrangements of the trees, while surface application of urea (U) and urea covered with ROS (U+ROS) were placed in the split plots. The losses of N by volatilization of ammonia (N-NH3) were quantified by means of a static semi-open system. Soil fluxes of N2O and CH4 were sampled by closed chambers and were determined by gas chromatography. Soil (0-10 cm) and climate parameters were monitored. Moreover, soil solution (40 cm depth) was collected by zero tension lysimeters for chemical analysis. The results were submitted to analysis of variance and Tukey test for comparison of means (P <0.10). Losses of NH3 from U+ROS-amended soil were 24% smaller than that in the soil with U, in average. However, there was no statistical difference between treatments. The presence of ROS did not increase significantly the N2O and CH4 emissions, maintaining the emission levels near to the baseline. Surface application of XR did not promote leaching of heavy metals such as Al, As, Cd, Pb to the soil solution at 40 cm depth, and did not significantly influence the presence of cations, COD, pH, EC and nitrate in solution from soil. Thus, the use of ROS together with nitrogen fertilization has a potential for use in agriculture, although more studies need to be carried out. The introduction of P. rigida trees in the native field did not significantly alter the CH4 and N2O fluxes of the soil, regardless of the plant spacing between the trees.