Uso e monitoramento de indicadores microbiológicos para avaliação da qualidade dos solos de cerrado sob diferentes agroecossistemas

Abstract

Although evaluating soil quality is a complex issue, its determination has been suggested as an important tool to assess the long term sustainability of agricultural ecosystems. The selection of which soil attributes will compose a soil quality index, their critical levels and their combination in a soil quality index are some of the difficulties to quantify soil quality. Chapter one evaluated the use of microbial biomass carbon (MBC) and soil enzyme activities as indicators of soil quality under different management systems in the cerrado region, comparing them to chemical (pH, organic matter, P, Ca, Mg, K, CEC and Al saturation) and physical (bulk density, macro, micro and total porosity) soil attributes. In march 2006, soil samples were collected to a depth of 10 cm in three areas: area I) corn/soybean rotation under no-tillage (NT) and conventional tillage (CT) initiated in 1992; area II) 16 year-old forest systems with pinus (Pinus tecunumanii), eucalyptus (Eucalyptus grandis) and a cerrado native species called carvoeiro (Sclerolobium paniculatum Vogel); area III) an experiment initiated in 1991 where annual cropping systems are integrated with pastures ( five treatments were evaluated: continuous grass pastures, continuous grass and legume based pastures, continuous annual cropping systems, annual cropping systems integrated with grass and legume based pastures and grass and legume based pastures integrated with annual cropping systems). Native cerrado fragments adjacent to the three areas were used as references. As compared to the CT, in area I, NT resulted in the accumulation of organic matter , nutrients, MBC and soil enzyme activities in the first 10cm. In area II, the MBC under the native cerrado areas was greater than under the forest systems. In this area, the lowest values of acid phosphatase and arilsulfatase were determined under pinus whereas the eucalyptus presented the greatest β- glucosidase activity. In area III, greater acid phosphatase and arylsulfatase activities were observed under the continuous grass and legume based pasture as compared to the continuous annual cropping system. PCA analysis showed that the microbial indicators presented the greatest sensibility to distinguish the agroecosystems evidencing the importance of their inclusion in a minimum data set to be considered in the studies and in the calculation of soil quality indexes. In chapter two, the software SIMOQS (Soil Quality Monitoring System), developed at the Viçosa Federal University, was used to calculate soil quality indexes (SQI) using chemical (pH, organic matter, P, Ca, Mg, K, CEC and Al saturation) , physical (bulk density, macro, micro and total porosity) and biological (microbial biomass carbon, β- glucosidase, acid phosphatase, and arylsulfatase activities) indicators and for monitoring soil quality under different management systems from 1998 to 2006. Soil samples were collected in areas 1 and 3 evaluated in chapter one. SIMOQS was an efficient tool to assess soil quality in the different agroecosystems evaluated. The benefits of pastures (particularly the legume based pasture), annual crops integrated with legume based pastures and of no-tillage systems were confirmed through their greater SQI.