Soil microbial community and activity in a tropical integrated crop-livestock system

Soil carbon (C) sequestration has been considered as a tool for mitigating increased atmospheric CO2. The soil C sink can be increased by the use of no-tillage, cover crops, crop rotations, and integrated crop-livestock systems (ICLS). ICLS is a strategy that replaces degraded pastures with silvopastoral systems to mitigate land degradation, but effects on soil biology are unknown. The objective of this study was to investigate the effect of Eucalyptus integrated with palisade grass on the soil microbial community and activity in the tropics. The study was conducted on an 8-year-old ICLS where two species of Eucalyptus (E. grancam and E. urograndis) were introduced into palisade grass [Urochloa brizantha (Hochst. Ex A. Rich.) R. Webster 'Marandu']. Four sampling locations were collected at 0 (planting line), 2, 4, and 6 m (middle of the plots) from the Eucalyptus tree. A monoculture palisade grass pasture and a native savanna (Cerrado) were included for comparison. Soil water content was lower closer to the Eucalyptus plantation line. The introduction of Eucalyptus into the system resulted in C and nitrogen (N) stocks in the Eucalyptus line similar to the Cerrado and the monoculture pasture, supporting the potential of ICLS and the monoculture pasture to recover soil C and N stocks. Soil microbial community composition and enzymatic activity (beta-glucosidase, acid phosphatase, and N-acetyl glucosidase) were reduced near Eucalyptus but increased in the pasture component of the ICLS likely due to improved soil water conditions. Soil microbial biomass, actinomycete, gram-positive bacteria, AMF, and fungi abundance were significantly higher in the native Cerrado than in the monoculture pasture and ICLS. Soil water, aggregate size, soil enzymes, and microbial communities were not dependent on the types of Eucalyptus species introduced into the system.