EFFECT OF NITROGEN FORMS AND RATES ON SOME HEAVY METALS AVAILABILITY AND RICE PRODUCTIVITY UNDER WASTEWATER IRRIGATION

Abstract

Water shortage in rice cultivation area in Egypt pushed rice farmer to use poor quality water in rice irrigation. Using the correct nitrogen form with the proper rate might be coping with the condition and possible heavy metals in such water. Two field experiments were conducted in 2010 and 2011 seasons at The Farm of Sakha Agriculture Research Station, Kafr-El Sheikh Governorate, Egypt. The soil texture was clayey. EC was 1.5dSm-1. The study aimed to find out the effect of various nitrogen forms; Urea, ammonium nitrate and ammonium sulfate with varying nitrogen levels of 0, 109, 146 and 219 kg N ha-1 on Nickel (Ni), Cadmium (Cd) and Lead (Pb) concentrations in soil, rice straw and rice grain as well as yield and yield components of Giza 178 rice variety under poor quality water .The chemical analysis of irrigation water was as following, Ni 0.28, 0.27, Cd 0.15, 0.17 Pb 0.34, 0.36 mg kg-1, ECw 2.66, 2.71 and pH 8.15 , 8.2 in the first and second seasons, receptively. Results indicated that the tested nitrogen forms and rate significantly affected the concentration of above-mentioned heavy metals, yield and yield components in both seasons. Ammonium sulfate was more efficient than other two nitrogen forms in minimizing heavy metals concentration in soil or rice plants and in enhancing yield and yield components under such poor quality water. The worst nitrogen form was ammonium nitrate regarding heavy metals concentration in plant or soil as well as yield and yield components of rice. Increasing nitrogen rate negatively affected the availability of heavy metals in soil, and their concentration in straw and grain of rice in both seasons. Furthermore, the increase nitrogen level (up to 146 kg ha-1) significantly improved yield and yield components of rice in both seasons.