Indicadores de saúde do solo em sistemas silvipastoris no semiárido

Abstract

The conversion of native environments into conventional cropping systems can degrade the soil and contribute to the emission of greenhouse gases (GHG) for the atmosphere. That's why, it should be advocated the adoption of conservationist management, which guarantee agricultural productivity and ecosystemic sustainability. Under this approach, the use of integrated production systems is a strategy to be adopted to assist in carbon (C) removal, GHG emissions mitigation and promote soil quality (SQ). Thus, the objective was to evaluate soil health indicators after the conversion of low-productivity pasture into silvopastoral systems in the semi-arid region of Bahia. The experiment was conducted in the municipality of Encruzilhada/BA, evaluating the following land uses: native vegetation (VN); low-productivity pasture of Urochloa decumbens (PBP); and two silvopastoral systems composed of Urochloa decumbens and Eucalyptus ugrogradis, with arrangement in single (SSP1) and quadruple (SSP4) rows of eucalyptus. Soil sampling was carried out in trenches up to 1 meter deep and then the following soil health indicators were evaluated: soil density (Ds); carbon (C) and nitrogen (N) contents and stocks; microbial biomass carbon (Cmic); microbial quotient (qMIC); activity of the enzymes β-glucosidase (βG) and Arylsulfatase (ARS); and soil fertility parameters. Additionally, they were selected seven soil health indicators (TOC, Cmic, βG, pH, K, P and DS) and it was determined the Soil Health Index (SS) using the Soil Management Assessment Framework (SMAF). The data were subjected to analysis of variance and the means compared by the Tukey test (p<0.05). They were observed lower DS in VN in the 0-10 cm layer and higher in PBP in the 10-20 cm layer. The conversion of PBP into SSP1 and SSP4 increased C contents and stocks at the evaluated depths. Cmic did not differ among treatments in the rainy season. However, it was higher in SSP1 and SSP4 in the dry season, which favored microbial biomass and qMIC in these systems. βG activity in the 0-10 cm layer did not differ among the land uses evaluated during the rainy season. However, lower enzyme activity was observed in PBP in relation to SSP1 and SSP4 in the dry season. ARS enzyme activity in the 0-10 cm layer was higher in VN and PBP in the rainy season, while in the dry season it was higher in SSP1, PBP and VN compared to SSP4. In the 10-20 cm layer, VN presented lower ARS activity compared to PBP. Principal component analysis (PCA) showed that silvopastoral systems improved soil chemical attributes. SMAF tool analysis demonstrated that the conversion of VN to PBP reduced health indices at the evaluated depths. However, the introduction of the SSP1 and SSP4 systems recovered and increased this index after seven years of conduction. Based on the responses of the soil health indicators and soil health diagnosis obtained in SSP1 and SSP4, it is concluded that the adoption of these systems improved soil health under the evaluated edaphoclimatic conditions.