Soil enzyme activities suggest advantages of conservation tillage practices in sorghum cultivation under subtropical conditions

Soil enzyme activity can be used as an indicator of soil quality for assessing the sustainability of agricultural ecosystems. The objective of this study was to determine the influence of conservation tillage practices, such as no tillage and reduced tillage (subsoil-bedding and shred-bedding), and conventional tillage practices, such as mouldboard ploughing, on physical–chemical, biochemical and physical soil quality indicators in a degraded sorghum field under warm subtropical conditions, after a period of 3 years. An adjacent soil under native vegetation was used as a standard representing local high quality soil. Conservation tillage systems, in particular no tillage, increased crop residue accumulation on the soil surface. Soil electrical conductivity and pH were not affected by the tillage practices. In the 0 to 5 cm layer, organic matter content increased with decreasing tillage intensity and was 33% greater with no tillage compared with the average of the other tillage treatments. The no tilled soil had higher values of water soluble C, dehydrogenase, urease, protease, phosphatase and β-glucosidase activities and aggregate stability than tilled soils, but had lower values than the soil under native vegetation. The enzyme activity and aggregate stability showed higher sensitivity to soil management practices than did physical–chemical properties. The no tillage system was the most effective for improving soil physical and biochemical qualities.