Waste Water Use in Crop Production: A Review

Paucity of quality fresh water for agriculture has made waste water (WW) application a popular option. Available data on chemical composition of different waste water, their effect on soil fertility, soil heavy-metal content, crop yield and quality parameters and maximum permissible limits (MPL) of different International environment protection agencies and governments of different countries has been summarized. Chemical composition of WW varied remarkably with respect to their heavy-metal content, pH, electrical conductivity (EC), biological oxidation demand (BOD), chemical oxidation demand (COD), alkalinity and hardness. Field application of all types of waste water significantly increases soil OC percentage, soil EC, cation exchange capacity (CEC), total and DTPA-extractable heavy-metal/micro-nutrient content, available macro-nutrient (N, P and K) content with significant decreases in calcium carbonate content of surface soil. However, high content of nitrogen, phosphorus and potassium strengthens its high fertigation/manural value for field crops. Significantly higher heavy-metal accumulation in soils irrigated with WW than ground water has been observed in surface layer than the lower depths of soil profile. Since crop genotypes and even crop cultivars within genotypes respond differently to waste water irrigation, their selection becomes more important under such situations. More importantly, carbon sequestration through WW irrigation could sustain long-term soil fertility. Periodic monitoring of chemical composition of waste water, soil and crop produce is however, suggested for safe and long term use of waste water.