Soil Organic Matter in Silvopasture and Brazilian Cerrado in Tropical Region.

Silvopasture, an agroforestry practice that combines trees with forage and livestock production, has recently gained prominence as an ecologically sustainable and environmentally desirable approach for managing degraded pasture lands. This system of planting trees on pasture lands is now becoming popular in Brazil, mainly for the possibility of carbon (C) sequestration in agroforestry system soils. Our objective was to investigate whether eucalyptus tree planting in pastures can increase soil C sequestration in tropical regions. The silvopasture system was composed of two eucalyptus hybrids: 1.) Grancam and 2.) Urograndis, both of which were integrated with the forage (Urochloa brizantha [Hochst. ex A. Rich.] R. Webster ‘Marandu’), spacing 2 m between plants and 12 m between eucalyptus rows in an 8-year plantating cycle. The soil was an Ultisol type with a dry winter and hot and rainy summer. Soil samples were collected from the eucalyptus line that was planted 2, 4, and 6 m in the silvopasture, and planted as pasture in the Brachiaria and Cerrado native areas as a control. The values of soil C and nitrogen (N) stocks were quantified in all systems. There were no significant differences in soil C stocks between the eucalyptus hybrids (Grancam and Urograndis). In the silvopasture system, there were no differences in the C and N stocks at different eucalyptus distances. The Cerrado and pasture (7.7 Mg C ha^-1 and 6.2 Mg C ha^-1, respectively) had the highest values of C stock in relation to the integrated system (4.7 Mg C ha^-1) in the soil surface layer (0‒5 cm). However, the C and N stocks in the deeper soil layers (5‒10 and 10‒20 cm) did not differ among the Cerrado, planted grasslands, and silvopastures.

Keywords: C sequestration, grassland, integrated system, eucalyptus, Urochloa