BIOTESTS AS MARKERS OF SOIL UTILIZATION AND FERTILITY

Two natural soil ecosystems, representative of agricultural management in a temperate Mediterranean climate, were selected: a sandy soil located al Peccioli Farm, Pisa (Italy), and a silt-loam soil located at Salamanca, Munovela (Spain). Within the systems, three areas were sampled (0-10 cm) during the dry season, each corresponding to a different soil use: native undisturbed (NS), cultivated (CS, crop-pasture rotation) and intensively cultivated soil (ICS, monoculture). Total C, N, exchangeable metals (Mn, Fe, Cu, Zn), ATP, urease, benzoyl-argininamide (BAA)-hydrolyzing and casein-hydrolyzing proteases, phosphatase, beta-glucosidase, and dehydrogenase were determined and compared. Exchangeable metals, ATP, enzyme activity, C, and N were found to be significantly higher (p = 1%) in native than in cultivated and intensive-agriculture soils. A good correlation (p = 5%) was found between ATP, hydrolases, C, and N, indicating that all these parameters are related to soil microbial biomass and activity in such ''low-energy'' ecosystems. Dehydrogenase did not correlate with C, N, and protease activities, meaning that the soil ecosystems have low concentrations of exogenous substrates to metabolize, and microorganisms were in a low state of activity. These parameters may be taken as markers of agriculture-induced changes in soil ecosystems.