Soil aggregate stability under different landscapes and vegetation types in a semiarid area in northeastern Syria

The influence of landscapes and vegetation types on soil aggregate stabilit y was studied at 55 sites in rangeland and 18 sites in cropland in northeas tern Syria. For the measurement of soil aggregate stability, the wet-sievin g test was applied to air-dried and prewetted aggregates. As soil propertie s, pH, EC, organic carbon content, inorganic carbon content, and sand conte nt were determined. Slope gradients at all the sites and soil surface cover age at the sites in the rangeland were also determined. Due to the slaking process, the stability of air-dried aggregates with a mean value of 47.5X10 (-2) kg kg(-1) was lower than that of prewetted ones with a mean value of 8 9.8X10(-2) kg kg(-1). The absence of a significant relationship between the soil aggregate stability and soil chemical properties in the cropland sugg ested; the influence of tillage. Principal component analysis and stepwise multiple regression analysis for the sites in the rangeland indicated that the air-dried aggregate stability could be described by a coverage factor a nd slope factor (r=0.76). The contribution of the coverage factor suggested that the increase of the soil organic matter content through the addition of plant materials and protection of the soil surface from the raindrop imp act could enhance the soil aggregate stability. The positive contribution o f the slope factor implied that unstable aggregates on steeper slopes had a lready been translocated, while stable aggregates remained. Thus, for the p reservation of the soil aggregate stability, the soil surface coverage shou ld be improved especially on gentler slopes.