Soil carbon and nitrogen stocks and the quality of soil organic matter under silvopastoral systems in the Brazilian Cerrado

This study investigated soil carbon and nitrogen stocks and quality of soil organic matter in an Eutric Haplic Cambisol four years after the conversion of degraded pastures into silvopastoral systems in the Brazilian Cerrado. The integrated production systems were composed of marandu grass (Urochloa brizanta) and Eucalyptus cloeziana or Eucalyptus urograndis. These systems were compared with areas of regenerating stratum and native vegetation of the Cerrado biome. A randomized statistical design was used, and soil chemical and biological attributes and soil CO2 efflux were evaluated (p < 0.05). After four years of implantation, soil carbon and nitrogen stocks increased in silvopastoral systems in relation to regeneration stratum, but were still lower than those in native vegetation. The chemical and granulometric soil fractionations indicated that carbon was protected in the most stable soil organic matter fractions (humin and silt + clay). There was an increase in soil microbial carbon during the rainy season and the metabolic quotient during the dry period. The deposition of plant material and soil tillage in silvopastoral systems composed of marandu grass (Urochloa) and Eucalyptus cloeziana contributed to an increase in soil microbial carbon at the 10-20 cm soil layer. The soil CO2 efflux, during the rainy and dry seasons, was similar between both silvopastoral systems and native vegetation, probably indicating greater diversity of organisms and roots in these systems than in regeneration stratum. We conclude that the introduction of integrated systems improved soil quality, allowing greater protection of soil organic matter.