Effects of Irrigation Water Sources on Soil Fertility, Heavy Metal Accumulation in both Soil and Rice (Oryza sativa L.)

Abstract Aims This study assessed the comparative impact of irrigation with sewage wastewater (SWW) and mixed sewage-industrial wastewater (SIWW) on soil fertility indicators and heavy metal accumulation in clayey soils and rice grains, using Nile water (NW) irrigation as a control. Materials and Methods Samples were collected from 21 sites in Dakahlia Governorate, Egypt, representing three irrigation sources: seven sites each irrigated by SWW, SIWW, and NW. Results Soils and rice grains from wastewater-irrigated sites showed significantly elevated levels of salinity, nutrients, organic matter, and bioavailable heavy metals compared to the Nile water control. Soil pH was the sole exception, showing no significant difference. SWW sources exhibited the highest levels of salinity, biochemical oxygen demand, nutrients, and heavy metals. This directly corresponded with elevated levels of these constituents in the soil and, subsequently, in rice grains, demonstrating a clear source-pathway-receptor linkage. Evaluation of soil fertility using the Applied System for Land Evaluation software classified into two classes: good-C2 under, and fair-C3 under. Heavy metal levels in soil, water, and plants were within safe limits. The contamination factor values followed the order: Ni ˃ Cd ˃ Cu ˃ Pb ˃ Zn. The pollution load index of soils under SWW was higher than that of soils under SIWW. Conclusions Wastewater is a valuable source of nutrients that significantly improves soil fertility. However, the associated accumulation of soluble salts and bioavailable cadmium, which entered the food chain, necessitates immediate, targeted monitoring and source control to ensure long-term agricultural sustainability.