Spatial cross-correlation of surface soil physicochemical properties with soil erosion estimated by fallout radionuclides in croplands in a semi-humid region of Iran

Abstract

Most attempts to correlate soil erosion rates with soil physiochemical properties have not fully succeeded. We employed 137Cs and 210Pbex tracers to understand the interactive impacts of medium- to long-term soil erosion rates on soil texture, structure, and composition in different cropping management systems and slope gradients. To do so, cultivated areas of a sub-watershed were subdivided into three iso-sectors based on slope gradient and typical cropping systems in the region: dry farming with slopes of 10–30 and < 10 % and irrigated farming with a slope of < 10 %. Some soil physiochemical properties were assessed, including particle size distribution, organic carbon (OC), aggregate percolation stability (PS), sealing index (SI), and semi-quantitative XRD of clays. The weighted average net erosion rates in cultivated lands estimated by 137Cs and 210Pbex methods were 26.3 and 31.4 Mg ha−1 yr−1, respectively. Among studied iso-sectors, the dry farming site with a slope of < 10 % had the highest net soil erosion rates and the lowest values for PS and SI, highlighting that land management is a more influential factor on soil erosion than the slope gradient. Both Pearson coefficient and spatial cross-correlation index (SCI) showed a negative correlation between clay content, aggregate stability and soil erosion due to the abundance of expandable clays in the region. However, unlike the Pearson coefficient, SCI showed that the soil loss rates had the strongest association with PS in space, but very weak ones with OC and SI, highlighting PS as a promising indicator of soil quality. SCI proved a superior analysis, which provides the spatial causality between the two variables in space. Findings suggest that to ensure food security in the face of future climate change, careful management practices should be implemented in dry farming lands with high amounts of expandable clays, making them prone to aggregate breakdown and soil erosion.