Improving soil surface properties: a driving force for conservation tillage under semi-arid conditions

The effect of long term conservation tillage (CT) application on soil organic carbon (SOC) concentration, and on stratification ratios (SR) of SOC, soluble organic carbon (SOCs), microbial biomass carbon (MBC) and protease activity (PA) has been studied. The SR was established dividing values of these variables at 0-5 cm depth by values at 10-25 cm depth. The results were compared with those obtained under traditional tillage (TT). The study was conducted in a wheat-sunflower crop rotation established in 1991 under rainfed conditions in south-west Spain. The results showed here correspond to the years 2001 (sunflower) and 2002 and 2004 (wheat). Despite a slight increase in SOC and the SR of SOC under CT compared to TT, noticeable and significant increases of SR of SOCs, MBC and PA were recorded in CT compared to TT. These increases reveal that the stratification of SOC under CT have consequences on soil functions beyond that of potentially sequestering more C in the soil. CT also improved soil quality by softening the loss of CaCO3, compared to TT. Additional key words: organic carbon, soil quality, stratification ratio.