Effect of Amendments on Bioavailability of Heavy Metals to Alfalfa and Biomass Yield Irrigated with Wastewater

Abstract

A field experiment was conducted to assess the effect of wastewater irrigation and various amendments on the bioavailability of metals to crops and its yield. Alfalfa was sown in 2×1-m plots receiving different amendments in a randomized complete block design with three replications. Five different amendments, farmyard manure (FYM; 10 t/ha), poultry manure (PM; 10 t/ha), humic acid (HA; 2.5 kg/ha), di-ammonium phosphate (DAP; 120 kgP/ha), and triple superphosphate (TSP; 120 kgP/ha) were applied to the soil prior to sowing crop along with a control receiving either wastewater or tubewell without amendments. The plants’ biomass results indicated that wastewater irrigation, when supplied with or without amendment, produced significantly higher yield (56% increase due to HA and wastewater application) than tubewell irrigation, indicating its nutritive value. Concentrations of Cu, Ni, Pb, and Fe accumulated by crop from wastewater were higher (84%, 94%, 112%, and 45%, respectively) and may cause phytotoxicity if untreated wastewater is used in the long term. Application of FYM, HA, and DAP reduced the uptake of metals, probably by forming insoluble complexes with metals; thus, they are recommended as amendments where wastewater is applied to decrease the possibility of heavy metals entering food chain.