SOIL CARBON AND NITROGEN IN SILVOPASTORAL SYSTEMS

Resumen

Silvopastoral systems are a good alternative for the recovery of degraded pastures. The objective of this study was to evaluate soil fertility, carbon and nitrogen stocks, the contribution of trees to carbon formation in the soil, and biological nitrogen fixation in silvopastoral systems in southern Espírito Santo. The experiment to evaluate the silvopastoral systems (SSP) was established in the municipality of Jerônimo Monteiro, ES, Brazil, with 5 treatments: Past: Pasture in monoculture; Eucal: Eucalyptus in monoculture; PE: Pasture and Eucalyptus in a Silvopastoral System; PEL: Pasture, Eucalyptus, and Leucaena in a Silvopastoral System; PA: Pasture and Araribá in a Silvopastoral System. Soil fertility, carbon and nitrogen stocks in the soil, the contribution of trees to carbon formation in the soil, and biological nitrogen fixation were analyzed. The treatments Past and PA showed the highest nutrient levels in the soil, attributed to low biomass absorption and composition above the soil in relation to the systems Eucal, PE, and PEL. Total organic carbon and total nitrogen levels tended to increase over time, while phosphorus, potassium, and sulfur showed a decrease in soil content. Carbon and nitrogen stocks in the soil did not show significant increases after 36 months of establishment in the silvopastoral systems. Only the Past treatment showed a higher nitrogen stock considering the depth up to 40 cm. Although no differences were found in the carbon and nitrogen stocks in the studied systems, a change in the surface soil (up to 5 cm) from a grass-derived C source to a tree-derived C source was observed in the Eucal and PE treatments. This was not observed in the nitrogen stock, where biological nitrogen fixation by legumes did not promote an increase in this nutrient in the soil.