Distribution Characteristics Of Methylmercury In Paddy Soil Under Different Farming Systems

Rice is one of the most important food crops in the world. China is the largest rice producing country in the world, and the annual grain production accounts for more than40% of the total grain output of the whole country. In recent years, it has been found that the rice has a strong ability of methyl mercury enrichment. The rice paddy soil is the main source of methyl mercury in rice, and rice consumption has become the main source of methyl mercury exposure in the mercury polluted area. Therefore, it is an important subject how to reduce the methylation of mercury in rice paddy system and inhibit the migration and accumulation of methyl mercury in rice plants, especially in grain. Long term different tillage methods had great influence on soil physical and chemical properties and microbial flora, which would affect the transformation,migration and accumulation of mercury in soil. However, it is not clear that the mechanism of the generation and accumulation of methyl mercury in rice paddy system under different tillage methods is not clear at present.Therefore, this study selected long-term experimental field, such as no-till winter paddy field(T1), ridge tillage no-till compartments for rotation field(T2), no-till province.with rotation field(T3), ridge tillage no-till province with rotation green fields(T4), ridge tilling for upland rotation field(T5), compartments for ploughing province with rotation field(T6), conventional culture winter paddy field(CK1) and conventional culture province.with rotation field(CK2), as the research object. Study on the dynamic change of methyl mercury in rice paddy system under different tillage patterns. To explore the distribution characteristics of methyl mercury in paddy soil under different tillage methods, and to find areasonable way to reduce the risk of exposure to methyl mercury in rice, and to provide scientific basis for farming management. Results show:1. Research from the whole test cycle(November to June), in the range of 0-10 cm soil depth, the total mercury content of T5 treatment was the highest, and the total content of mercury in soil of T6 treatment was the lowest. In the range of 10-20 cm soil depth, the total mercury content of T3 treatment was the highest, and the total content of mercury in soil of CK1 treatment was the lowest. In the range of 20-30 cm soil depth,the total mercury content of CK2 treatment was the highest, and the total content of mercury in soil of T1 treatment was the lowest. Research on the whole soil profile, the total mercury concentration was highest in the soil depth of 0-10 cm, and the total mercury concentration was lowest in the 20-30 cm range of the depth of the soil layer.There was no significant difference in the range of 0-30 cm soil depth.2. Research throughout the test period(November to June), in the range of 0-10 cm soil depth, the methyl mercury content of T1 treatment was the highest, and the methyl mercury content of CK2 treatment was the lowest. In the range of 10-20 cm soil depth, the methyl mercury content of T1 treatment was the highest, and the methyl mercury content of T3 treatment was the lowest. In the range of 20-30 cm soil depth,the methyl mercury content of T3 treatment was the highest, and the methyl mercury content of T4 treatment was the lowest. Research on the whole soil profile, within the range of 0-30 cm soil depth, the methyl mercury content of various performance test of paddy soil is: T1>T2>T3>T6>T5>T4>CK1>CK2. This indicates that ridge tillage especially in winter paddy field ridge tillage better results in an increase in paddy soils methylmercury content.The conventional flat upland rotation field is particularly conventional flat as more conducive to reducing soil methylmercury paddy.Recommend the use of conventional rotation tillage, can effectively reduce the methylmercury content in paddy soil.3. After planting rice paddy, mercury and methyl mercury in the paddy field occur continuously from the soil to the water body. During the cultivation of rice,upland crop rotation farming methods more favorable than the winter paddy paddy increase in total mercury content in soil and water, but winter paddy farming methods to better promote mercury methylation process soil.4. At seedling stage in rice, for no tillage paddy rice upland crop rotation,compared with compartments for processing, ridge tillage processing is more conducive to soil mercury to the interstitial water; as for ploughing province.with rotation field, compared with ridge tillage processing, compartments for processing is more conducive to soil mercury travel to the interstitial water; No tillage process is more conducive to methylation for treatment of Ridge- upland Rotation paddy, conventional flat is more conducive to methylation for processing compartments. In the rice Young Panicle Development Stage and the flowering and fruiting stage, for no tillage paddy rice upland crop rotation, compared with ridge tillage processing, compartments for processing is more conducive to increased mercury content. As for ploughing province.with rotation field, compared with compartments for processing, ridge tillage processing is more conducive to increased mercury content; conventional flat is more conducive to methylation for processing compartments.5. In seedling stage in rice and Rice Flowering and fruiting period, compared with upland rotation rape, upland rotation green manure can help increase the mercury content in paddy system. In Rice Panicle Development stage, green manure rotation tillage can promote the release of mercury from the soil to the water.