Soil Erodibility Factor Analysis

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Soil Erodibility Factor (K)
The soil erodibility factor (K), a measure of the susceptibility of soil to erosion under standard conditions, is a function of the percentage of silt and coarse sand, the soil structure, the permeability of the soil, and the percentage of organic matter. Wischmeier et al. (1971) defined the soil erodibility factor mathematically and Foster et al. (1996) converted the equation into the following SI unit equation:
The soil erodibility factor (K) is determined for each soil sample based on analysis of soils in laboratory. The equation (Wischmeier and Smith, 1978) mentinoned is below.
K = ((2.17 × 10-4) × (M1.14) × (12-a) + 3.25 × (b - 2) + 2.5 × (c - 3)) × d [5] where M = (percentage of silt and fine sand)
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C factor is a ratio comparing the soil loss from land under a specific crop and management system to the corresponding loss from continuously fallow and tilled land. Although the USLE was developed for use on agricultural fields, the appropriate C factor are used for nonagricultural conditions.
For this study, C factor values were taken from the USLE project results (Türkseven ve Ayday, 2000) carried out at the basin for agricultural areas and based on literature data published in Canga (1995) for forest, pasture and shrub. C factors for agricultural areas (wheat-fallow system), forest, shrub, pasture and water surface were considered 0.15, 0.001, 0.20, 0.01 and 0.0, respectively.
Support Practice Factor (P)
It reflects the effects of practices that will reduce the amount and rate of the water runoff and thus reduce the amount of erosion. The P factor represents the ratio of soil loss by a support practice to that of straight-row farming up and down the slope. The most commonly used supporting cropland practices are cross-slope cultivation, contour farming and strip
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For that reason P factor was accepted as 1.00 for entire basin.
3. RESULTS and DISCUSSION
Topographic map at a scale of 1:25000 published by the General Directorate of Rural Affairs (KHGM) was used as the base map. All data including soil, topography and land use obtained via remote sensing techniques and field observations from the basin were digitized in ArcInfo software and analysed with ArcView 3.1 software. All factors of the USLE was converted to grid size of 10×10 m for estimating of soil erosion rates within the basin. After completing the input data, R, K, LS and C factor maps were multiplied in GIS environment and provided the soil loss (A) map given in Figure 8.
Mean soil loss of the basin was estimated as 4.9 ton ha-1year-1. Soil loss for agricultural, pasture, shrub+agricultural and forest were estimated as 6.4, 10.78, 0.42 and 0.12 t ha-1, respectively (fig.

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