University of Tehran Press Iranian Journal of Soil and Water Research 2008-479X 56 6 2025 08 23 Aggregate stability and organic carbon distribution in two land uses of pasture and olive orchard: a case study, Rostamabad, Iran Aggregate stability and organic carbon distribution in two land uses of pasture and olive orchard: a case study, Rostamabad, Iran 1663 1683 103847 10.22059/ijswr.2025.393060.669921 FA Abbas Shabani Rofchaee Department of Soil Science, faculty of agriculture, University of guilan, Rasht, Iran Mahmoud Shabanpour Department of Soil Science, faculty of agriculture, University of Guilan, Rasht, Iran Sepideh َAbrishamkesh Department of Soil Science, faculty of agriculture, University of guilan, Rasht, Iran Journal Article 2025 04 12 Aggregate stability is considered one of the key indicators in evaluating soil structure and is significantly influenced by land use, vegetation cover, and other physical and environmental characteristics of the soil. This study examines aggregate stability indices and aggregate-associated organic carbon in surface soil, as well as the mean weight diameter of aggregates in subsurface soil, across three slope positions. Soil sampling was conducted under two land uses including an olive orchard (with under-canopy and inter-row positions) and the adjacent natural pasture at two depths: 0–10 cm and 30–40 cm. The results of the analysis of variance showed that both land use change and slope position had significant effects on the mean weight diameter, geometric mean diameter, and fractal dimension of aggregates in surface soil. The highest increase in mean weight and geometric mean diameter of aggregates was observed in the under-canopy position of the olive orchard. Additionally, a significant decrease in the fractal dimension of aggregates was found under the olive canopy. In contrast, lower values of mean weight and geometric mean diameter and an increase in fractal dimension were observed in various positions within the pasture and the inter-row spaces. Furthermore, the results regarding the organic carbon associated with surface soil aggregates indicated that larger aggregates are responsible for the stabilization and protection of organic carbon in all three studied sites. The results also confirmed that aggregate stability decreases with increasing soil depth, and this decline was more pronounced in the rangeland area. Aggregate stability is considered one of the key indicators in evaluating soil structure and is significantly influenced by land use, vegetation cover, and other physical and environmental characteristics of the soil. This study examines aggregate stability indices and aggregate-associated organic carbon in surface soil, as well as the mean weight diameter of aggregates in subsurface soil, across three slope positions. Soil sampling was conducted under two land uses including an olive orchard (with under-canopy and inter-row positions) and the adjacent natural pasture at two depths: 0–10 cm and 30–40 cm. The results of the analysis of variance showed that both land use change and slope position had significant effects on the mean weight diameter, geometric mean diameter, and fractal dimension of aggregates in surface soil. The highest increase in mean weight and geometric mean diameter of aggregates was observed in the under-canopy position of the olive orchard. Additionally, a significant decrease in the fractal dimension of aggregates was found under the olive canopy. In contrast, lower values of mean weight and geometric mean diameter and an increase in fractal dimension were observed in various positions within the pasture and the inter-row spaces. Furthermore, the results regarding the organic carbon associated with surface soil aggregates indicated that larger aggregates are responsible for the stabilization and protection of organic carbon in all three studied sites. The results also confirmed that aggregate stability decreases with increasing soil depth, and this decline was more pronounced in the rangeland area. https://ijswr.ut.ac.ir/article_103847_51be8e24eeaf7605e9591d6acd73e5fb.pdf