Soil biochemical indicators as a tool to assess the short-term impact of agricultural management on changes in organic C in a Mediterranean environment

Two management systems (conventional vs. organic) in a 3-years crop rotation (pea-durum wheat-tomato) were compared after 4 years in order to assess soil carbon (C) changes in a short-term period. Biochemical properties of soil, such as microbial biomass C and N (MBC and MBN), microbial respiration, N mineralization, dehydrogenase, chitinase, acid-phosphatase, arylsulfatase and beta-glucosidase activities, were chosen as indicators of soil organic matter biochemical alteration. The main questions addressed in this study were (1) do soil biochemical properties discriminate between organic and conventional management systems in a short-term period? (2) Which biochemical indicator is more effective in predicting soil organic C accumulation in organically managed agricultural soils? A general increase of hydrolytic enzymes activities has been observed in soil under organic management. MBC, MBN and the MBC/TOC ratio (q(mic)) increased in organic soil under pea (100%, 50% and 100%, respectively) and durum. wheat (55%, 28% and 42%, respectively), while the basal respiration per unit of microbial biomass (q(CO2)) decreased (48% and 40% under pea and durum wheat, respectively). Moreover, the specific activity of beta-glucosidase was significantly lower under organic management of pea and durum wheat and was positively correlated with q(CO2), suggesting a lower maintenance energy requirement of the microbial community. Soil microbial biomass and enzymatic activities were successfully used to detect short-term changes in soil and, taking into account its role in soil functioning, beta-glucosidase resulted the most suitable indicator to predict organic C accumulation in soil under organic management in a Mediterranean environment. (C) 2008 Elsevier Ltd. All rights reserved.