Assessment of the quality indices of soils irrigated with treated wastewater in a calcareous semi-arid environment

Abstract

Abstract The investigation of soil quality indices as affected by treated wastewater (TW) irrigation is essential to prevent and control soil degradation mainly in rapidly developing nations. To reveal more details of this aspect, a research experiment was conducted on 17 soil attributes in the topsoil belonging to six various soil sites that had been irrigated with TW (five sites) and freshwater (one site as control). The integrated soil quality index (SQI) of the TW-irrigated sites and the control site was compared using both the Total Data Set (TDS) and Minimum Data Set (MDS) approaches. The results showed that TW irrigation adversely affected soil salinity-sodicity indices, including electrical conductivity (EC), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP) by 18–147% and heavy metals (Zn, Cu, Cd, Pb, and Ni) by 0.36–3 times. This suggests to a negative and degrading impact on soil quality. In contrast, soil fertility indices [total N, available P, organic matter, and cation exchange capacity (CEC)] and exchangeable cations (Ca, Mg, and K) were positively increased by 10–70% and 15–164% after irrigation with TW, respectively. Such changes imply to a positive and improving effect on soil quality. SQI values using the TDS (SQI-T) and MDS (SQI-M) approaches showed III grade of soil quality in all soil sites under TW irrigation and control. Following TW irrigation, a rise of 6% to 16% and 5% to 11% was recorded in the values of SQI using the TDS and MDS approaches, respectively. However, no change occurred in the grade of soil quality after TW irrigation. The contributions of EC, available P, Cd, CEC, and OM were the highest to SQI-T while CEC, EC, Cd, and OM showed the highest contribution to SQI-M. The regression equations showed that 76–83% and 68–74% of the variations in yield data of wheat could be captured by SQI-T and SQI-M, respectively.