MICROBIAL INDICATORS IN THREE AGRICULTURAL SOILS WITH DIFFERENT MANAGEMENT.

Microorganisms respond rapidly to changing environmental conditions. Therefore microbes are generally considered as sensitive indicators of soil health. The aim of this study was to assess the biological fertility status and sustainability of three differently managed agricultural soils by using microbial indicators. Management practices involved a soil with minimum treatment (biodynamic); a soil characterized by periodic application of manure and chemical fertilizer (manure); and a soil characterized by depurated and stabilized organic sludge amendment (sludge). Samples were taken four times during a year, at two depths: 0-15 and 15-30 cm. An extensive characterization of soil organic matter was carried out. Biochemical parameters included metabolic quotient, mineralization quotient and kinetic parameters of microbial decomposition of soil organic matter. Community level physiological profile analysis (CLPP) was used to investigate soil microbial energetic strategies adopted in differently managed soils. Total amounts of fungi and bacteria were determined by direct microscopy. Indicators related to labile and humic organic matter fractions suggest significantly lower soil fertility and lower sustainability in the sludge amended treatment. Differences between the biodynamic treatment and Manure treatment were less consistent. Eco-physiological quotients and kinetic parameters of C-mineralization indicated a steady state in the biodynamic treatment and stressed conditions in the sludge treatment. Microbial communities seem to adopt a typically K-strategy (persistent) in the bio-dynamic treatment and a typically r-strategy (opportunists) in the sludge treatment. Manure management shows an intermediate result: the superficial layer is characterized by r-strategists and the deeper layer by K-strategists. [ABSTRACT FROM AUTHOR]