Tillage Effects on Soil Quality Indicators in the Semi-Arid Mediterranean Coastal Plain of Turkey

Tillage affects the chemical, biological and physical properties of agricultural soils and influences several soil quality indicators. We examined the effects of different tillage systems on selected soil quality indicators in the semi-arid Mediterranean Coastal Plain of Turkey. Five tillage practices were evaluated: conventional tillage with stubble burning (CT1), conventional tillage with stubble (CT2), minimum tillage (MT), rotational tillage (RT) and no-tillage (NT). The tillage treatments were used for winter wheat (Triticum aestivum), summer corn (Zea mays) and crop rotation of corn and winter wheat. Bulk density, aggregate stability, plant available water, wilting point, field capacity water, organic carbon content and penetration resistance of the soil were evaluated. Conservation tillage systems (MT, RT and NT) increased organic carbon content, aggregate stability and plant available water. Comparisons between samples collected in 2004 and 2006 showed that MT increased organic carbon by 7% at a soil depth of 0-10 cm whereas RT increased it by 10-20% at a depth of 0-20 cm. Aggregate stability was improved by 8-21% in the CT2, MT, RT and NT plots, but it decreased by 6% in the CT1 plot at 20-30 cm depth. Available water increased from 11-71% in the MT, RT and NT treatments. The lowest bulk densities were found at the 0-10 cm depth in the MT (1.42 Mg m-3), 10-20 cm depth in the CT1 (1.44 Mg m-3) and 20-30 cm depth in the NT (1.45 Mg m-3) treatments, respectively. Penetration resistance in tilled soils (CT1, CT2 and MT) was lower compared with those in RT or NT treatments from the surface up to 15 cm, but differences among tillage systems at 15-40 cm depth were not significant. We conclude that conservation tillage practices (MT, RT and NT) can provide better soil characteristics than conventional practices in the semi-arid soil of the Mediterranean coastal plain. However, especially, in semi-arid climatic regions, more long-term experiments are needed to quantify the effects of tillage on soil quality indicators.