Active carbon and biological properties as indicators of soil quality in dryland Mediterranean farming

Abstract

Soil quality indicators of changes derived from different tillage managements are required. We studied the short (3 years) and long-term (16 years) effects of conservation tillage (CT), in comparison to traditional tillage (TT), on soil organic carbon fractions (total organic carbon, TOC and active carbon, AC) and biological properties (microbial biomass carbon (MBC) and β-glucosidase activity) on a sandy clay loam soil (Xerofluvent) located in semi-arid SW Spain. A rainfed crop rotation (cereal-sunflower-legumes) was established in both trials. Soil samples were taken in flowering (in March) and after harvesting (in July) of a pea crop and collected at three depths (0-5, 5-10 and 10-20 cm). Contents of AC and MBC in the long-term and content of AC in the short-term were higher in CT than in TT in the upper layer. In July sampling, β-glucosidase values were higher at the top-soil under CT in both trials. The studied parameters decreased with increasing depth in both tillage systems (TT and CT) and in both trials. β-Glucosidase values presented high correlation coefficients with AC and TOC contents in the long-term trial. There was not correlation for both TOC and MBC with others parameters in the short-term trial. In this study, the AC content is reported as the most sensible and reliable indicator for assessing the short- and long-term impact of CT on soil quality under our conditions.