Effect of Tillage and Residue Management on Selected Soil Quality Indicators Under Mediterranean Conditions.

Soil organic carbon (SOC) plays an important role in maintaining soil quality of agro-ecosystems. Depletion of SOC is a widespread dilemma under rainfed low-input conditions in Mediterrean environments, especially when crop residues are removed as livestock fodder and soils are repeatedly tilled. As a soil conserving measure, zero tillage (ZT) and residue retention has been suggested as a viable solution to maintain or even increase SOC contents. In this study the effects of tillage on soil organic matter, soil aggregation, as well as soil organic matter fractions (humification) was assessed under ZT as well as conventionally-tilled (CT) plots, with or with only little stubble retention at ICARDA headquarters in the north of Syria. After four years of distinct land management practices, SOC content at 0-2 cm depth was 20-30 % higher under ZT than under CT. Overall, an increased level of humification, possibly contributing to more decomposed soil organic matter under CT was detected by measuring the optical absorbance spectra of humic acids. Aggregate stability of the 0.5-0.2 mm soil fraction, as well as its stratification ratio was a sensitive indicator for the impact of tillage. A higher SOC and more stable aggregates under ZT are signs for improved soil quality.