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Water shortage and soil qualitative degradation are significant environmental problems in arid and semi-arid regions of the world. The increasing demand for water in agriculture and industry has resulted in the emergence of wastewater use as an alternative in these areas. Textile wastewater is produced in surplus amounts which poses threat to the environment as well as associated flora and fauna. A 60-day incubation study was performed to assess the effects of untreated textile wastewater at 0, 25, 50, 75, and 100% dilution levels on the physico-chemical and some microbial and enzymatic properties of an aridisol soil. The addition of textile wastewater provoked a significant change in soil pH and electrical conductivity and soil dehydrogenase and urease activities compared to the distilled-water treated control soil. Moreover, compared to the control treatment, soil phosphomonoesterase activity was significantly increased from 25 to 75% application rates, but decreased at 100% textile wastewater application rate. Total and available soil N contents increased significantly in response to application of textile wastewater. Despite significant increases in the soil total P contents after the addition of textile wastewater, soil available P content decreased with increasing concentration of wastewater. Changes in soil nutrient contents and related enzymatic activities suggested a dynamic match between substrate availability and soil N and P contents. Aridisols have high fixation and low P availability, application of textile wastewater to such soils should be considered only after careful assessment.

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Application of raw and treated wastewater for irrigation is an extensive practice for agricultural production in arid and semiarid regions. Raw textile wastewater has been used for cultivation in urban and peri-urban areas in Pakistan without any systematic consideration to soil quality. We conducted a laboratory incubation study to investigate the effects of low C/N ratio raw textile wastewater on soil nitrogen (N) contents, labile carbon (C) as water-soluble C (WSC) contents, and activities of urease and dehydrogenase enzymes. The 60-day incubation study used an alkaline clay loam aridisol that received 0 (distilled water), 25, 50, and 100% wastewater concentrations, and microcosms were incubated aerobically under room temperature at 70% water holding capacity. Results revealed that raw wastewater significantly (p < 0.05) changed soil N pools and processes, WSC contents, and enzymatic activities. The organic and inorganic N species increased with increasing wastewater concentrations, whereas WSC contents followed an opposite trend. The highest NH-N and NO-N contents were observed in soil treated with 100% wastewater. The extractable organic N (EON) contents always represented >50% of the soil total Kjeldahl N (TKN) contents and served as the major N pool. However, nitrification index (NO-N/NH-N ratio) decreased at high wastewater concentrations. A significant negative correlation was observed between EON and WSC (p < 0.05) and between net nitrification and WSC/EON ratio (p < 0.01). In contrast, nitrification index and WSC contents were correlated, positively suggesting WSC potentially controlling N turnover in nutrient-poor aridisol. We found significant (p < 0.0001) positive correlations of soil urease and dehydrogenase enzymatic activities with soil-extractable mineral N contents indicating coupled N cycling and soil biological activity. Higher production and accumulation of soil NO-N and EON contents in concentrated wastewater-treated soil could pose an ecological concern for soil fertility, biological health, and water quality. However, the EON could lead to mineral N pool but only if sufficient labile C source was present. The effects of wastewater irrigation on soil N cycling need to be assessed before it is recommended for crop production.