Control Of Rice Cadmium Contamination Through Heavymetal Passivants And Foliar Fertilizers

Recently, arable land is adversely affected by cadmium contamination throughout the world via excessive exploitation of mineral resources, residual effects of industrial effluents, overuse of chemical fertilizers and pesticides and blind use of sewage irrigation to farmland. The safety and quality of agricultural products are the major concern worldwide because of food contamination by metals including cadmium. Rice is a staple food in China and covered a large area, therefore, to ensure its production safety is of great importance. Commonly, cadmium contamination of rice is a major threat to human health. The main objective of the present study was to produce brown rice with minimum accumulation of Cd that is under the safe limits for human consumption. To achieve above mentioned goal, different kinds of passivants and foliar fertilizers were designed to conduct the pot and field experiments of rice in Cd contaminated soil. The obtained results are summarized as follows:1. Four soil Cadmium passivants(Si, SG, FM and FA) were designed to minimize the accumulation of Cd in brown rice by means of soil pot experiments. All the passivants reduced Cd content and accumulation of rice, but the efficiency varied with the type of soil and rice varieties. Cd content and accumulation in brown rice of early rice grown in brown red soil decreased by 26.75%~63.81% and 36.50%~65.60% respectively under low level(0.30%~0.15%) of passivants application, while in calcareous alluvial soil Cd content and accumulation decreased by 41.68%~53.38% and 30.77%~52.52% respectively. Even so, Cd content of early rice couldn’t meet with the national cadmium standard of the food safety and quality. Moderate application levels(0.50~1.00%) of Si, SG and FA passivants had good effects on late rice, Cd content and accumulation in brown rice of late rice grown in brown red soil decreased by 74.33%, 55.85%, 31.78% and 74.33%, 55.85%, 31.78% respectively. Cd content and accumulation in brown rice of late rice grown in calcareous alluvial soil decreased by 72.25%, 49.05%, 27.38% and 71.71%, 4.16%, 24.67% respectively. Almost all the late rice after treatments had low Cd content, which are consistent with the national food safty standards. Among these four passivants, Si showed the most effective results and FM illustrated the least ones, SG had a less effect than Si, but a better effect than FA.2. Generally, the passivants reduced the uptake of Cd by converting it from available forms to unavailable forms in soils which could not be uptaken by rice plants. Improvement in oxidative stress and decrease in lipid peroxidation level might be thereasons for rice to accumulate less Cd. Application of Si, SG and FA passivants could reduce sharply the MDA and GSH content of rice grown in brown red soil. Si and FM passivants could improve antioxidant enzymes’ activity of rice grown in calcareous alluvial soil. When applied with Si passivants, soluble protein content of rice grown in both soil was increased significantly.3. Application of foliar fertilizers also reduced the availability of Cd. Rice cultivars showed different responses to foliar application of fertilizers. As compared to control, in soil pot experiment, the Cd content and accumulation of brown rice in early rice were decreased by 24.34%~58.21% and 28.43%~65.59% respectively, while in late rice were decreased by 9.61%~88.72% and 7.27%~88.30% respectively. Late rice plants accumulated less amount of Cd which was under the criteria developed by National Food Safety except treatments CK2 and ACNP. Foliar fertilizers SS1, SS2 and SS3 had good effects on both rice cultivars.4. The foliar application of fertilizers also had the ability to alleviate the oxidative damage induced by Cd in rice plants. In pot experiment, MDA and GSH contents were significantly reduced as comparied with the control in late rice leaves when treated with foliar fertilizers, however, treatments XPN and ACNP showed non-significant results. SOD activity was slightly increased with the application of foliar fertilizers except treatment CK2.5. There were no negative effects observed with any passivants in late rice plants. Passivants of Si, SG, FAand foliar fertilizer of SS3 and CK3 significantly enhanced the yield of late rice cultivar.6. Results from field experiment of late rice showed that both base fertilizer and foliar fertilizers could decrease Cd content in brown rice by 24.58%~62.07%. One or two times of foliar Spraying with double dose of SP1 got a better effect. Comparied with SP1 and SZSP3, SZSP2 was less effective. Application of silicon and silicon + zinc reduced the available Cd in soil. Silicon showed better results to reduce the uptake of Cd than combination with other amendments.7. Field experiment found that all amendments(e.g. foliar fertilizers SST, SSH, SA, PA and DXZ) significantly reduced the Cd uptake by the early rice. The accumulation of Cd in different tissues of early rice was varies greatly with the application of different treatments. In conclusion, among the five foliar fertilizers, SST and SSH were more effective than DXZ and PA, while SA was the least effective.