Domestic sewage irrigation on dynamics of nutrients and heavy metals in soil and wheat (Triticum aestivum L.) production

Background Evaluation of urban sewage for its feasibilityand potentiality as sources of irrigation water and plantnutrient is need of the hour. In this context, a field experimentwas laid out in split–split plot design with threereplications. Main plots constituted two types of lands(fields irrigated with sewage and bore well water since1992). Subplots were allotted with three sources of irrigationwhich consisted of sewage water alone, bore wellwater alone (good water) and conjunction of sewage andbore well water. And sub-subplot constituted of four fertilizerlevels (no fertilizer, 50 % recommended rate offertilizer (RRF), 75 % RRF and 100 % RRF.Results Crop growth in terms of photosynthesis, netassimilation rate and dry matter production significantlyincreased in sewage-irrigated land compared to bore wellirrigatedland. Similarly, significantly higher wheat grainyield (4370 kg ha-1), protein (12.88 %) and dry gluten(9.22 %) were obtained in field irrigated with sewage watercompared to bore well-irrigated land. Sources of irrigationalso differed significantly producing higher grain yield(4,100 kg ha-1), protein (12.81 %), dry gluten (8.97 %) insewage irrigation compared to bore well water irrigation.Enhanced activity of dehydrogenase and phosphataseenzymes and organic carbon in sewage-irrigated fieldcontributed more to available nutrient pool of soil. Pooledresults of 2 years revealed that wheat roots accumulatedsignificantly higher amount of Cr, Ni, Pb and Cd in sewage-irrigated land compared to bore well-irrigated land.The same trend was noticed in stem with respect to Cr andNi. In general, concentration of heavy metals was higher inroot followed by stem and lower in grain. The Pb concentrationin plant parts (root, stem and grain) was notinfluenced by land type and sources of irrigation. None ofthe treatments did show accumulation of these heavymetals in wheat plant parts more than normal range foundin food plants. The values of these metals were below therecommended maximum tolerable levels proposed by theJoint FAO/WHO Expert Committee on Food Additives,Summary and conclusions. In: 53rd Meeting, Rome,(1999).Conclusion Increased wheat grain yield in sewage-irrigatedland compared to bore well-irrigated land wasattributed to increased soil fertility that was a result ofcontinuous sewage irrigation. Long-term irrigation of farmlands with wastewater leads to contamination of soil andplant system with heavy metals in the study area. Wastewater-irrigated soil showed significant (p.05,p.01) accumulation of heavy metals compared to thefreshwater-irrigated soil indicating concern of theirincreased absorption in wheat plant. The accumulation ofheavy metals in wheat plant was in the order of roots[-stems[grains. However, all these heavy metals in plantsystem were lower than the recommended threshold level.