RESEARCH ARTICLE Low C/N ratio raw textile wastewater reduced labile C and enhanced organic-inorganic N and enzymatic activities in a semiarid alkaline soil Mahnaz Roohi 1 & Muhammad Riaz 1 & Muhammad Saleem Arif 1 & Sher Muhammad Shahzad 2 & Tahira Yasmeen 1 & Muhammad Arslan Ashraf 3 & Muhammad Atif Riaz 4 & Ishaq A. Mian 5 Received: 29 July 2016 /Accepted: 11 November 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Application of raw and treated wastewater for irriga- tion 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 ac- tivities of urease and dehydrogenase enzymes. The 60-day incubation study used an alkaline clay loam aridisol that re- ceived 0 (distilled water), 25, 50, and 100% wastewater concen- trations, and microcosms were incubated aerobically under room temperature at 70% water holding capacity. Results re- vealed 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 4 + -N and NO 3 - -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 3 - -N/NH 4 + -N ratio) de- creased at high wastewater concentrations. A significant nega- tive 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 control- ling N turnover in nutrient-poor aridisol. We found significant (p < 0.0001) positive correlations of soil urease and dehydroge- nase enzymatic activities with soil-extractable mineral N con- tents indicating coupled N cycling and soil biological activity. Higher production and accumulation of soil NO 3 - -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. Keywords Textile wastewater . Soil nitrogen . Extractable organic nitrogen (EON) . Water-soluble carbon (WSC) . Soil enzymes Introduction Application of wastewater for irrigation is a widespread practice in arid and semiarid regions of the world including Pakistan due to shortage of water (Hamilton et al. 2007; Qadir et al. 2007). According to a global estimate, 18% of agricultural production is irrigated, accounting for 40% of all food production; out of this cropping area, 20 million ha in more than 50 countries is irrigated Responsible editor: Zhihong Xu * Muhammad Riaz mr548@ymail.com 1 Department of Environmental Sciences & Engineering, Government College University Faisalabad, Faisalabad 38000, Pakistan 2 Department of Soil & Environmental Sciences, University College of Agriculture, University of Sargodha, Sargodha, Pakistan 3 Department of Botany, Government College University Faisalabad, Faisalabad 38000, Pakistan 4 Soil Science Division, Nuclear Institute for Agriculture and Biology (NIAB), Jhang Road, Faisalabad, Pakistan 5 Department of Soil & Environmental Sciences, University of Agriculture Peshawar, Peshawar, Pakistan Environ Sci Pollut Res DOI 10.1007/s11356-016-8102-2