Biogeochemical Behavior of Lead and Nickel as Influenced by Phosphatic Fertilizer Applied to Rice (<i>Oryza sativa</i> L.) Cultivars Grown under City Effluent Irrigation

The hydrology of arid to semi-arid regions is substantially different from that in humid regions due to scarce hydrological data distributions with dry climates and strong evapo-transpirative conditions. In the perspective of global water shortage, food security for all of the living beings has become a matter of great concern. Efficient use of water resources both in urban and rural environments and application of non-conventional water resources for irrigation are becoming increasingly important. In order to sustain crop production, the re-use of treated wastewater for irrigation of crops could be a good option. A pot experiment was set up to evaluate effects of different doses of di-ammonium phosphate (DAP) fertilizer on lead (Pb) and nickel (Ni) phyto-availability by two cultivars of rice irrigated with city effluent. Experiment was conducted in a completely randomized design (CRD) each with three replications. The results showed effective immobilization of Pb with applied phosphatic fertilizer. Among all of the tested treatments, the most effective treatment to reduce phyto-availability of Pb was T₄ (248 kg P ha⁻¹) due to antagonistic interaction. While Ni showed inconsistent behavior with both synergistic and antagonistic interaction (biphasic) to applied phosphorus (P) rates. Data regarding various growth parameters such as plant height, number of tillers, shoot and root dry weights, straw and grain yields, and physiological attributes such as total chlorophyll contents, photosynthetic and transpiration rates showed significant (<i>p</i> ≤ 0.05) responses to P application. An increasing trend was revealed in determined parameters with increased P application rates, with the exception of decreased plant height. The conclusion of the present remedial approach indicated that addition of P can significantly reduce the risks of rice grown under city effluent irrigation containing high Pb and Ni contents.