## 4 Discussion
### Effects of Irrigation with TWW on Soil Chemical Properties  
The present study reported an increase in soil pH and EC post-irrigation with TWW (Table 1). Soil pH increased by 9%, and soil EC increased by 293%. Irrigation with TWW in this study led to an increase in soil pH by 0.73 units and EC by 54.297 mS/m. [PERSON] et al. [33] reported that irrigation with TWW led to an increase in soil pH by 0.8 units. The similar change in soil pH between the present study and that of [PERSON] et al. [33] is most likely due to the presence of similar basic substances in TWW, as [PERSON] et al. [33] also reported an alkaline pH range of 7.1 to 8.6 during their study. However, there is no consensus on the outcome of irrigation with TWW on soil pH since the chemical ingredients of TWW are different with each region, thus affecting soil pH and EC differently. Acceptable pH and EC values in soil for crop production range between 6.5 and 8.4, and 250 mS/m and 750 mS/m, respectively [32]. Thus, irrigation with TWW in this study led to an increase in soil pH outside of the acceptable threshold of 6.5 to 8.4. However, soil EC was within the acceptable threshold for crop production. Previous studies reported that an increase in soil EC increases the solubility of non-essential toxic elements, thus increasing the bioavailability of non-essential toxic elements [34; 35]. Nevertheless, the fate of toxic elements in soils is a function of soil geochemical properties, mainly soil pH. When soil pH is greater than 7, As and Cr have high mobility, and at a soil pH less than 7, the solubility of Cd and Pb increases [36]. An increase in SOC by 3-fold post-irrigation with TWW was observed (Table 2). SOC is an ingredient of TWW, and it is represented by the high BOD of TWW in Table 1. The results of the present study are substantiated by previous studies that have reported a significant increase in SOC post-irrigation with TWW [37; 38]. [PERSON] et al. [38] attributed the increase in SOC to the chemical ingredients of TWW such as nutrients and organic compounds. However, some previous studies have reported that the increase in SOC caused by irrigation with TWW is temporary due to the rapid mineralization of SOC by soil microbes [39; 40]. Nevertheless, the increase in SOC can improve soil properties, thus improving the quality of ecosystem services rendered by soils [41]. Furthermore, an increase in essential elements post-irrigation with TWW was observed (Table 2), which is substantiated by previous studies as there were no fertilizers added to the soil [37; 42]. [PERSON] et al. [39] reported an increase in P and K post-irrigation with Olive Mill Wastewater. [PERSON] et al. [42] reported an increase in soil N and P in plant tissues post-irrigation with wastewater. [PERSON] and [PERSON] [43] reported that extractable P was high in soil irrigated with TWW compared to freshwater. [PERSON] et al. [44] attributed the increase in soil nutrient status to the chemical constituents of TWW. The addition of essential elements via irrigation with TWW can mitigate the ecological and economic risks attached to the usage of fertilizers for crop production. The increase in the essential nutrients such as nitrates can decrease fertilizer application by 10-15% [45]. The increase in non-essential toxic elements post-irrigation with TWW within a 12-week irrigation period is a serious concern due to the health risks associated with the accumulation of non-essential elements on the trophic level [46]. The present study observed that irrigation with TWW for 12 weeks on a sandy-loam-textured soil led to an increase in non-essential toxic elements in soil by 31%, 54%, 25%, 110%, and 31% for As, Cd, Pb, Al, and Cr, respectively, as reported in Table 2. However, the increase in the concentration of non-essential toxic elements in soil post-irrigation with TWW does not result in the toxic elements exceeding the WHO/FAO threshold in the soil [47,48].