Abstract

Soil Organic Carbon (SOC) plays a major role in nutrient cycling as the primary sink and source of plant nutrients, water holding, soil infiltration, soil aggregation and soil health. This study was conducted in the rangelands of Kermanshah, Iran within five land-use practices including normal rangeland (NR), overgrazed rangeland (OR), fired rangeland (FR), converted rangeland in rain-fed orchard (CRO) and converted rangeland in rain-fed (CRR). 57 soil samples were taken from these sites and subjected to soil samples analyses, especially soil organic carbon (SOC) and aggregate size distribution (ASD). Results showed that the respective mean SOC in the NR, OR, FR, CRO and CRR include 3.32, 1.16, 1.02, 2.13 and 1.22%. There was significantly (P≤ 0.05%) higher in NR than others. Course aggregate class in the NR and CRO were significantly (P≤ 0.05%) more than others due to light grazing and higher SOC while fine aggregate size was found significantly different from each other. Fine aggregate size was higher in the CRR (20.42 %) and OR (18.40 %) compared to NR. It occurs through, up to down the slope plough and lower SOC value. The fire and overgrazing are second and third improper activities which negatively affect SOC and soil aggregation.

Key words: Aggregate size distribution, normal rangeland, soil organic carbon, different grazing, converted rangeland.