Document Type : Research Paper
Former Graduated Student, Department of Soil Science, College of Agriculture, Islamic Azad University, Khorasgan Branch, Isfahan, Iran
Assistant Professors, Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan, Iran
Associate Professors, Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan, Iran
The present study was conducted to investigate the effects of slope gradient and land use changes on aggregate stability and on Soil Organic Carbon (SOC) pools in aggregate size fractions in western Iran. Three land uses in the study area, namely: Natural Forest (NF), Disturbed Forest (DF) and Cultivated Land (CL) as well as three slope gradients (0-10%, S1, 10-30%, S2, and 30-50%, S3) were selected for soil sampling. A total of 99 soil samples were taken from the 0-10 cm depth of the surface layer within the whole studied hilly region. The results revealed that forest disturbances and continuous cultivation following deforestation significantly decreased soil Water Stable Aggregate (WSA) fraction, Mean Weight Diameter (MWD) as well as Geometric Mean Diameter (GMD) values within the three selected slope classes. The highest content in percent of macro-aggregates (2.00-4.75mm) and of meso-aggregates (0.25–2.00mm) were detected in the lower slope (S1) induced by higher C stocks in this site. The highest percentage of macro-aggregates was observed in the natural forest soil and while the highest micro-aggregates (0.053-0.25mm) observed in the cultivated and disturbed forest soils. There were significant SOC differences observed among the three land uses for macro- aggregates, but no significant differences identified for meso- and micro-aggregates as between disturbed forest vs. cultivated soils. The results also revealed significant differences among the gradient slopes concerning SOC and TN in aggregates for the three land uses, with the lowest ones observed in the steep slopes (S3) with the highest soil erosion rate. The relative distributions of total nitrogen along with C/N ratios among the aggregate fractions were in mach with the SOC distribution.