Abstract
Abstract In the Universal Soil Loss Equation (USLE), soil erodibility factor K can be estimated by using a regression equation that has been presented based on field erosion plots in relatively non-calcareous soils. Therefore, it seems necessary to determine the estimating error of the regression equation in calcareous soils of Iran. This study was conducted in an agricultural area with a dimension of 30 km in Hashtrood province, northwest of Iran during March 2005-2006. The studied soils had about 1.1% organic matter and 13% lime (TNV). In order to investigate the soil erodibility, 36 regular grids of 5×5 km were considered on the study area. On each grid, three standard plots with 1.2 m intervals were established in dryland farming area having a 9% south hill slope. The actual soil erodibility value of the plots was determined as the annual soil loss per annual rain erosivity factor under natural rainfall events. The K value was estimated using the USLE regression equation. Soil physical and chemical properties were measured in samples taken from 0 to 30 cm depth. The results indicated that mean actual value of the soil erodibility factor in the study area was 0.004258 Mg.h.MJ-1.mm-1 which is 10.75 times smaller than the estimated K-factor. There was a poor correlation (R2= 0.16) between the actual and estimated soil erodibility factor. The estimating error values of the soil erodibility varied from 3.173 to 39.298 with a mean error of 9.984. There was a significant correlation between the calcareous soil erodibility and the amount of coarse sand, silt, organic matter and lime (TNV) of the soil. Regression analysis showed that the calcareous soil erodibility significantly (R2= 0.80, p<0.001) was affected by coarse sand, organic matter and lime. Coarse sand, organic matter and lime decreased the calcareous soil erodibility at the statistical levels of 0.001, 0.01 and 0.001, respectively. Key words: Soil erodibility factor, Calcareous soils, USLE, Hashtrood province
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