Effects of long-term tillage practices on organic carbon of different aggregate sizes and available water content

In this study, long-term (2006-2014) effects of six different tillage systems on aggregate size distribution, organic carbon distribution among different sized aggregates and water holding were investigated in a soil contained approximately 50% clay under Cukurova conditions. The tillage treatments are; Conventional tillage with stubble (moldboard plowing) (CTS), Conventional tillage with stubbles burned (CTB), Heavy disc harrow reduced tillage (RTD), Rototiller reduced tillage (RTR), Heavy disc harrow zero soil tillage (RNT) and no till or zero tillage (NT). The most frequently encountered aggregates in all tillage systems were at 4.0-2.0 mm size and the 1.0-0.5 mm size aggregates were the least frequently found aggregates. The rate of >4.0 mm and 4.0-2.0 mm macro-aggregates increased in the conservation tillage systems compared to conventional tillage systems. The aggregates with the highest organic C content were at 1.0-0.5 mm size and the aggregates with lowest organic C content were at 2.0-1.0 mm size. Aggregate-associated organic C contents in 0-15 cm depth were higher under conservation tillage systems compared to the conventional tillage systems, though organic C contents at 15-30 cm depth were greater mainly in conventional tillage systems. The mean weight diameter values increased in the conservation tillage practices (NT) compared to the conventional tillage practices (CTS and CTB) 204% and 137%, respectively. Although it wasn't different specifically among other tillage practices, the highest available water contents were obtained in RNT practice and RNT practice had significant effects on retained water in soil.