Sustainable agriculture in oman: evaluating treated wastewater irrigation effects on soil quality, heavy metal accumulation, and alfalfa growth

Abstract Water scarcity in arid regions like Oman necessitates sustainable irrigation alternatives such as treated wastewater (TWW). This study evaluates the long-term impact of TWW, mixed water, and groundwater irrigation on soil properties, heavy metal accumulation, and alfalfa ( Medicago sativa ) growth in the Ash-Sharqiyah North Governorate. Physicochemical analyses of soils and alfalfa shoots from 12 farms revealed significant site-specific variations in parameters such as pH, electrical conductivity (EC), sodium adsorption ratio (SAR), and organic matter (OM). Soils irrigated with TWW exhibited lower salinity and heavy metal concentrations compared to those near sewage treatment plants (STP) or irrigated solely with groundwater. Nickel (Ni) and chromium (Cr) levels in soils near STP and control sites exceeded FAO/WHO limits, likely due to long term waste water discharge. However, bioaccumulation in alfalfa remained below safety thresholds which suggesting limited plant uptake under current soil conditions. Contamination and enrichment indices confirmed TWW’s role in minimizing metal accumulation. Alfalfa showed efficient uptake of nutrients like potassium (K), phosphorus (P), and chloride (Cl), with boron (B) being the only heavy metal with a bioaccumulation factor (BAF) > 1 across all sites. Salinity, organic substance content and lithography were found to be the main factors influencing variance in metal dynamics using PCA analysis. Alfalfa cultivated using TWW irrigation was safe for animal consumption even though the soil had some elevated metal levels. So, prolonged use of TWW may increase metal accumulation, highlighting the importance of long-term monitoring. In order to enhance the adoption of TWW in agriculture, awareness programs for farmers, provision of supportive policies, subsidies and cost-effective treatment technologies are necessary. These measures can build trust and encourage large scale implementation of TWW in water scarce regions.