ChileanJAR

A Santa Bárbara andisol, that had been under different no tillage conservation systems for several years was evaluated to assess the effect of various soil use on soil organic matter (SOM) composition and stability. Samples we're taken from the following soil use and management systems: forest, natural pasture, implanted prairies, and intensive crop rotation. In addition, cropping systems with and without liming were evaluated. Methods previously adapted for chilean volcanic soils were used for the study of SOM parameters (SOM fractioning, carbohydrates, C-biomass and dehydrogenase (DH) determination). Organic carbon in the mineral and organic fractions were determined. The various soil uses and management systems had no effect on SO1M loss, as observed in other tillage methods. On the other hand, SOM levels were high, near 11% ofweighted C for the first 30 cm. The quality ofthis SOM is very stable; 70% as humine carbon and humid acids, and 30% in fulvic acids and carbohydrates, the most active organic matter (OM) fractions. Bioactivity and carbohydrate content showed important fluctuations in the samples taken in the two years under study. The decrease ofthe carbohydrate corresponded to an increase in dehydrogenase activity (DH), which implies greater activity in C mineralization.