Effects of growing seasons and genotypes on the accumulation of cadmium and mineral nutrients in rice grown in cadmium contaminated soil.

Heavy metals naturally occur in soil but their concentrations may be changed by seasonal rainfall under double-rice cropping system. The field trials at three sites, which represent low, medium and high cadmium (Cd) content in soil, revealed significant genotypic and environmental variations in grain Cd concentrations. Most cultivars in late rice at three sites produced grains with Cd content over the maximum permissible concentration (MPC) 0.20mgkg-1. However, grain Cd content in early rice was over MPC only at high Cd site. When planted at same site, late rice showed remarkably higher content of Cd as well as K, Mg, Fe and Mn than that in early rice in both grains and rachises. Content of Ni, Pb and Cr was generally in the safe range and it was determined by the interactions between genotypes and environmental factors. Element concentrations in rachises were about 2-10 times higher than those in grains, depending on element species, cultivars, locations and seasons. Low-Cd-accumulation cultivars generally displayed both lower Cd content in rachis and lower Cd transportation ratio from rachises to grains than those of high-Cd-accumulation cultivars. There was a significant and positive correlation between Cd and Mn concentrations in grains. The most important factor that causes great variation in Cd accumulation in rachises and grains between early and later rice is water contents and levels in paddy soils mainly caused by different rainfall amount. Inhibiting Cd accumulation in rachises and Cd transportation from rachises to grains could efficiently decrease Cd content in rice grains produced in contaminated soil.