The main objective of this study was to map soil erodibility in the mountainous rangelands of Kyrgyzstan. The results of this effort are expected to contribute to the development of soil erodibility modelling approaches for mountain areas. In this case study we map soil erodibility at two sites, both representing grazing rangelands in the mountains of Kyrgyzstan and having potentially different levels of grazing pressure.
We collected a total of 232 soil samples evenly distributed in geographical and feature space. Then we analyzed the samples in a laboratory for grain size distribution and calculated soil erodibility values from these data using the Revised Universal Soil Loss Equation (RUSLE) K-factor formula. After that we derived different terrain indices and ratios of frequency bands from ASTER DEM and LANDSAT images to use as auxiliary data because they are among the main soil forming factors and widely used for prediction of various soil properties. Soil erodibility meaningfully correlated with channel network base level (geographically extrapolated altitude of water channels), remotely sensed indices of short-wave infrared spectral bands, exposition and slope. We applied multiple regression analysis to predict soil erodibility from spatially explicit terrain and remotely sensed indices. The final soil erodibility model was developed using the spatially explicit predictors and the regression equation and then improved by adding the residuals.
The spatial resolution of the model was 30 meters and the estimated mean adjusted coefficient of determination was R2 = 0.47. The two sites indicated different estimated and predicted means of soil erodibility values (0.035 and 0.039) with 0.95 significance level, which is attributed mainly to the considerable difference in elevation.