بررسي تاثير بقاياي زراعت ديم بر فرسايش خاك درمناطق خشك ونيمه خشك جنوب ايران

Evaluation of the Impact of Rain Fed Farms Mulches on Soil Erosion in the Arid and Semi Arid Region in South of Iran

Stubble mulches on [he rain ted farms will increase the shear strength of topsoil against overland flow. The evaluation of flow resistance of crop residuals in the arid and semi arid min len farms in south of Iran is very important. Because in these regions. the rainfall regime i:-. very intense. especially in spring und summer seasons, and if (here b not suitable vegetation cover on the earth, erosion rate is increased. In this research an open flume with 15m length, 0.3111 width and (J.5m height was used to simulate overland now 011 the native rangeland around the city of Larncrd, which is located ut u distance of 380 kilometers from southwest of Shiraz. In order to compare the rain fed farms mulches I""ith pasture vegetation. four treatments including rain fed faun mulches. poor, moderate and good pastures with vegetation density < 20%, 20 10 40% and >40% were respectively examined. Also for evaluation ofthe stem height of rained farms 011 erosion. three treatments including rain fed farm mulches with 0, 10 and 20 cm height were examined. For each treatment, four to five discharges from low to high were used and hydraulic parameters such us discharge, depth and sediment were measured and other parameters sUl:b as mean velocity. Darcy-Wcisbcch friction factor and shear strcs... were calculated. Results or this study show that the relationship betv..ʹcen shear stress and sediment is linear and the critical shear stresses for erosion initiation wertʹ 23.75. 20AS, 28.55 nnd 45.70dyn,-,,!cm1 lor rain ll:d farm mulches, poor, moderate and good ranges respectively and the threshold of sheet erosion of crops residuals is higher than poor pasture and Jess than moderate and good so that with changing good ranges to rain ted farms, thi..ʹ 110\,,· resistance is decreased. On the other hand. the stem height of crops residuals effect flow resistance and erosion. and in this research the optimum height of crops residuals was 10 em.