Effect of long-term wastewater irrigation on the quality of alluvial soil for agricultural sustainability

To evaluate the effects of using wastewater in alluvial soil irrigation for long periods on soil quality (SQ), Bahr-Elbaqar study location was chosen (32 degrees 15' to 32 degrees 09' E and of 30 degrees 58' to 31 degrees 07' N). The SQ assessment was carried out using 15 soil features belonging to seven soil locations; six irrigated with wastewater for different periods and one control location irrigated with freshwater. The soil quality index (SQI) of the seven locations was calculated using either total data set (TDS) or minimum data set (MDS) methods. The principal component analysis was utilized to recognize soil characteristics for the MDS. The results indicated that using wastewater in irrigation negatively influenced the soil salinity status represented by electrical conductivity (EC) exchangeable sodium percent (ESP), and sodium adsorption ratio (SAR) by 62-107%, 17-52% and 31-80%, respectively. Available heavy metals (Pb, Cd, Cu and Ni) increased with increasing the irrigation periods and the highest mean values were in location 6 that been irrigated for >42 years implying an adverse and degrading influence on soil quality. In contrast, irrigation with wastewater enhanced some soil indicators including organic matter (OM), total N (T-N), available P, K (A-P and A-K), and cation exchange capacity (CEC) indicating a constructive and enhancing influence on soil quality. The contributions of pH, EC, ESP, A-P, A-Cd and OM were the highest and chosen as MDS to calculate MDS-SQI. Most of the examined area classified in Moderate class either using the TDS or MDS.