Investigating the spatial distribution of soil wind-erodible indices using geostatistical methods in the Sistan plain

The study of land erodibility and its spatial modeling is the main and key information for sustainable land management. Wind erosion is one of the main environmental hazards in Sistan region. Therefore, this research aimed to investigate the spatial changes and modeling of wind erodibility indices in the Sistan Plain. For this purpose, 181 points were selected over the plain, and surface soil was sampled. The studied indices included the laboratory wind-erodible fraction (EF), the wind-erodible fraction based on Fryrear formula (EFF), López formula (EFL), Bouajila formula (EFB), soil crust factor (SCF), dry aggregate stability (DAS) and the soil erodibility. Also, some physical and chemical characteristics were measured in soil samples using standard methods. IDW, kriging, and cokriging were used as geostatistical analysis methods. The results showed that the best variogram model for EFF, SCF, EFB, and DAS was the spherical model, and for EFL, EF, and soil erodibility was the exponential model and the spatial fit for all indices was in the average spatial fit class. The best predictive methods were simple cokriging with covariate of sand for EFF (RMSE=5.724) and soil erodibility (RMSE=85.576), with covariate of clay for EFB (RMSE=2.950) and DAS (RMSE=14.481) and with covariate of sand to clay ratio for EF (RMSE=17.966) and ordinary cokriging method for SCF (RMSE=0.163) and EFL (RMSE=36.312) with covariate of sand to clay ratio. The average values of EFF equal to 29.13%, SCF equal to 0.45%, EFL equal to 75.25%, EFB equal to 83.09%, EF equal to 54.97%, DAS equal to 72.18% and soil erosion equal to 121.67 Mg ha-1 yr-1. The highest values of wind-erodible indices were observed in the southern parts of the Sistan plain, and, the lowest values were observed in the northern and western parts. However, the highest value of DAS was found in the northern and western parts and the lowest in the southern part of the plain. There was a high match between the spatial distribution of erodibility indices and the spatial distribution of soil particle size. The changes in soil mineral particles in the region depend on the geomorphic nature of the region and are in line with the changes in the sedimentation regime of the Hirmand River and its branches, as well as wind erosion and sedimentation processes in the Sistan Plain.