Intensity of tillage practices can enhance organic matter decomposition, increasing CO 2 emissions from soil to the atmosphere. Conservation tillage (CT) has been proposed as a means of counteracting potential damages to the environment. In this study the effects of two CT systems, reduced tillage in a long-term experiment (RT L ) and no-tillage in a short-term experiment (NT S ), were compared to traditional tillage (TT) in the long (TT L ) and short-term experiments (TT S ). CO 2 fluxes, total soil organic carbon (SOC) and dehydrogenase activity (DHA) were evaluated at 0-5, 5-10 and 10-15 cm depths throughout the three years studied (Oct. 2006-Jul. 2009). Traditional tillage increased CO 2 emissions compared to CT. The CT treatments (RT L and NT S ) accumulated more SOC in the surface layer (0-5 cm) than the TT treatments (TT L and TT S ). SOC accumulation was moderate but DHA consistently increased in CT in the surface soil, especially with a legume crop included in the crop rotation. Values of stratification ratio of all parameters studied were higher in the CT treatments (RT L and NT S ). The agricultural and environmental benefits derived from CT make this system recommendable for semi-arid Mediterranean rain-fed agriculture.