title: Low C/N ratio raw textile wastewater reduced labile C and enhanced organic-inorganic N and enzymatic activities in a semiarid alkaline soil.
abstract: 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 NH4+-N and NO3--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 (NO3--N/NH4+-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 NO3--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.
authors.affiliation: Department of Environmental Sciences & Engineering, Government College University Faisalabad, Faisalabad, 38000, Pakistan.
authors.forename: Mahnaz
authors.initials: M
authors.lastname: Roohi
authors.affiliation: Department of Environmental Sciences & Engineering, Government College University Faisalabad, Faisalabad, 38000, Pakistan. mr548@ymail.com.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Riaz
authors.affiliation: Department of Environmental Sciences & Engineering, Government College University Faisalabad, Faisalabad, 38000, Pakistan.
authors.forename: Muhammad Saleem
authors.initials: MS
authors.lastname: Arif
authors.affiliation: Department of Soil & Environmental Sciences, University College of Agriculture, University of Sargodha, Sargodha, Pakistan.
authors.forename: Sher Muhammad
authors.initials: SM
authors.lastname: Shahzad
authors.affiliation: Department of Environmental Sciences & Engineering, Government College University Faisalabad, Faisalabad, 38000, Pakistan.
authors.forename: Tahira
authors.initials: T
authors.lastname: Yasmeen
authors.affiliation: Department of Botany, Government College University Faisalabad, Faisalabad, 38000, Pakistan.
authors.forename: Muhammad Arslan
authors.initials: MA
authors.lastname: Ashraf
authors.affiliation: Soil Science Division, Nuclear Institute for Agriculture and Biology (NIAB), Jhang Road, Faisalabad, Pakistan.
authors.forename: Muhammad Atif
authors.initials: MA
authors.lastname: Riaz
authors.affiliation: Department of Soil & Environmental Sciences, University of Agriculture Peshawar, Peshawar, Pakistan.
authors.forename: Ishaq A
authors.initials: IA
authors.lastname: Mian
mesh_terms: D000468:Alkalies / Q000737:chemistry; D002244:Carbon / Q000032:analysis* / Q000378:metabolism; D055598:Chemical Phenomena; D058465:Nitrification; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D013784:Textiles; D062065:Wastewater / Q000737:chemistry*
chemical_list: D000468:Alkalies; D002244:Carbon; D009584:Nitrogen; D012987:Soil; D062065:Wastewater
keywords: Extractable organic nitrogen (EON); Soil enzymes; Soil nitrogen; Textile wastewater; Water-soluble carbon (WSC)