A comprehensive assessment of soil degradation linked to treated wastewater irrigation in the cultivated semi-arid region

Utilizing wastewater for agricultural irrigation is receiving growing attention worldwide as a valuable strategy to mitigate water scarcity, particularly in the water-stressed regions. However, wastewater reuse may have implications for soil degradation indicators. This study, conducted in 2024, comparatively assessed soil degradation indicators in smallholder farmlands irrigated with treated wastewater (TWW) and fresh water (FW). Two versions of a comprehensive soil degradation index (CSDI) were developed using 18 indicators: one that utilizes a total dataset (CSDI-TDS) and another that relies on a minimum dataset (CSDI-MDS) for both adjacent farms irrigated by TWW and FW. Physical degradation indicators, such as bulk density (BD), soil stability index (SSI), soil crusting index (SCI), and modified clay ratio (MCR), showed only minor changes between TWW- and FW-irrigated farms, ranging from just 2 to 8%. In contrast, chemical indicators, including electrical conductivity (EC), sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), and soil organic carbon (SOC), exhibited dramatic increases of 25–73%, while soil heavy metals surged by 25–243% following TWW irrigation. This divergence clearly establishes salinization, sodification, and heavy metal accumulation as the dominant drivers of soil degradation in the study region, whereas physical structural deterioration remains comparatively limited. Compared to FW-irrigated farms, the mean CSDI-TDS and CSDI-MDS values in TWW-irrigated farms increased by 2–12% and 7–13%, respectively, across all farms, confirming that TWW application promotes overall degradation. Both CSDI models explained 31–37% of the variance in corn yield data, underscoring their practical relevance. Our findings highlight that CSDI-based assessments, particularly the CSDI-MDS framework, serve as robust, cost-effective tools for quantifying soil degradation in the TWW-irrigated croplands. Crucially, management strategies must prioritize mitigating chemical and heavy-metal risks rather than focusing primarily on physical soil rehabilitation.