Risk of heavy metals accumulation in soil and wheat grains with waste water irrigation under different NPK levels in alkaline calcareous soil.

A field study was conducted on the reuse of wastewater from Mardan city to evaluate its risk of contaminating soil and wheat grains at different NPK levels. Three irrigation sources i.e. waste water (WW), canal water (CW) and alternate waste + canal water (WW+CW) were applied to wheat (cv Atta Habib 2010) grown at 0, 50, 75 and 100% NPK levels of 120:90:60 kg N:P2O5:K2O ha-1 at Palatoo Research Farm, Amir Muhammad Khan Campus, Mardan during 2015.The results showed higher grain and biomass yields in WW irrigated plots as compared to CW at NPK levels up to 50% of recommending dose revealing supplementing nutrient requirements in deficient conditions. However, irrigation of WW at higher NPK levels especially at or beyond 75% of recommended dose tended to reduce the crop yield that could be associated with heavy metals toxicity and nutritional imbalances. The use of WW substantially increased AB-DTPA extractable Zn, Mn, Pb, Ni and Cd indicating a potential threat to soil contamination. Similarly, WW irrigated wheat had higher concentrations of these heavy metals as compared to CW which limits its use for production purposes without any remediation measures. The alternate use of CW and WW as revealed by its comparative lower contamination in soil and wheat than sole WW could be one of the possible solutions and may increase the time required for threshold soil contamination.