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چکیده
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Soil shear strength is a fundamental mechanical property that influences various soil behaviors and interactions during tillage. Continuous cultivation can significantly alter soil mechanical properties, including shear strength. This study aimed to investigate changes in shear strength parameters in soils cultivated with sugar beet and canola. Eight soil profiles were excavated in fields planted with these two crops in the Gyan Plain, selected based on land suitability classifications. Each profile was described and sampled, and the physical and chemical properties of the soils were analyzed as predictors of surface shear strength across all horizons. Shear strength parameters were determined using the standard direct shear test, from which stress–shear curves were generated to calculate cohesion and internal friction angle. Correlation analysis revealed a significant positive relationship between cohesion and soil organic matter (r = 0.35, P < 0.05), while no significant relationship was found with clay content. Cohesion showed significant negative correlations with specific density (r = –0.37, P < 0.05) and internal friction angle (r = –0.70, P < 0.01). The angle of internal friction exhibited a significant positive correlation with both soil depth (r = 0.35, P < 0.05) and specific density (r = 0.56, P < 0.01), but a significant negative correlation with organic matter (r = –0.56, P < 0.01) and moisture content (r = –0.62, P < 0.01). Regression analysis confirmed a negative correlation between cohesion and the internal friction angle, with an R² of 0.53. The results indicated that shear stress was higher in soils under sugar beet cultivation compared to those under canola, while the modulus of elasticity (E) was greater in canola-cultivated soils. Overall, this study identified crop type and root system, soil moisture, specific density, organic matter content, and soil developmental stage as key factors influencing soil shear strength. To improve soil shear strength, it is recommended to adopt crop rotation strategies and avoid monoculture systems.
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