Study On Phytoremediation And Safe Utilization Of Cadmium-contaminated Purple Paddy Soil

To solve the cadmium（Cd）pollution in purple paddy soil of Chongqing area,screening test of rice varieties with low heavy metal accumulation of multi-objective elements,study on Cd accumulation in rice by several heavy metal barrier materials such as biomass charcoal,silica calcium fertilizer,straw organic fertilizer and Nano-silica sol,study on intercropping between Cd accumulation high aquatic plants and Cd accumulation low rice was conducted respectively by using in situ field experiment.To filter out low Cd accumulation of rice varieties adapted to local conditions,provide the basis for the rice production safety,and then choose to rice varieties used in follow-up studies,respectively to investigate application of heavy metal resistance of materials in situ passivating repair measures and intercropping mode of plant restoration measures to breed rice Cd accumulation of target and paddy field safety utilization,in order to establish a set of purple paddy soil for Cd pollution production and repair technology pattern.The results show that:（1）The 13 rice varieties in chongqing exhibited significant genotype differences between each other,the extreme values of Cd,As,Pb and Cr in different rice varieties can be more than 3,4,20 and 3 times different,respectively,the same rice varieties of different heavy metals accumulation ability is also very big difference,low heavy metal accumulation of rice varieties screening should be in a variety of pollution elements as the goal,at the same time 13 kinds of rice yield difference is very big also tested between 5.85～10.65 t·hm^-2,the difference between extremes is 44.8%.The influence of genotype differences on heavy metal accumulation of rice varieties was the largest in rice,followed by stem,leaf and root.The transfer coefficient TF_SL-G from stem to leaf to grain was an important embodiment of rice genotype differences,and was positively correlated with heavy metal content in rice（P<0.01）.By using the heavy metal comprehensive accumulation index（P_Z）,the comprehensive heavy metal accumulation ability of rice varieties tested was divided into three categories:low（P_Z<0.7）,medium（0.7≤P_Z<1）and high（P_Z≥1）.In consideration of rice yield and heavy metal accumulation in rice,Long liangyou 534,Y liangyou 1,Yuan liangyou 908 and Yu xiang 203 are recommended as suitable varieties in Chongqing,which can not only achieve high yield but also benefit the safe production of rice.（2）Heavy metal barrier materials,including Si-Ca fertilizer,straw organic fertilizer,biomass charcoal and foliar nano-silica sol,can significantly reduce the content of Cd in rice,which is conducive to the safe production of rice.Among them,soil application of biomass charcoal,silicon-calcium fertilizer and straw organic fertilizer can reduce the available Cd in soil by adjusting soil pH and soil physical and chemical properties,and their optimal applied doses are 3 t·hm^-2、4.5 t·hm^-2 and 2.49 t·hm^-2,respectively,and the Cd content in rice decreases by 68.8%,74.1%and 59.4%,respectively.Foliar nano-silica sol can inhibit Cd transport from leaf to rice,the content of Cd in rice was reduced by 77.7%.On impedance control effect,nano silicon sol on the leaf>calcium silicon fertilizer>biomass charcoal>straw organic fertilizer.Among them,the application of foliar nano-silica sol can not only significantly reduce the content of Cd in rice,but also make the rice on the stem and leaf has a high amount of Cd extraction,conducive to the guarantee of food safety and the removal of Cd in the soil,field operation is high,the application prospect is the best.（3）The heavy metal barrier materials,including biomass carbon,silicon calcium fertilizer and organic fertilizer,in addition to being able to inhibit rice Cd accumulation,there will be conducive to rice production,to varying degrees of increase rice yield,the corresponding maximum yield and growth are:10.2 t·hm^-2,25.9%、8.83 t·hm^-2,8.6%、9.62 t·hm^-2,18.5%,biomass carbon performed best.Biomass charcoal,silica calcium fertilizer and straw organic fertilizer combined with foliar nano-silica sol can promote the increase of rice yield,proving that foliar nano-silica sol could also improve rice yield.In addition,although straw organic fertilizer has a strong effect on the promotion of rice yield,straw organic fertilizer often contains certain Cd in the material due to the problem of fermentation production process,which becomes a drawback that cannot be ignored.（4）Under the intercropping mode of rice with high Cd（Yu zhenxiang）and low accumulation（Chang liangyou 772）,there was antagonism between varieties on the absorption and accumulation of heavy metals and other nutrient elements,compared to a single variety of rice monoculture,intercropping mode two rice varieties of Cd content in rice were decreased,the reduction range is Chang laingyou772:25.4%～52.3%,Yu zhenxiang:21.4%～32.3%,the intercropping model had a stronger inhibitory effect on Cd accumulation in rice with low Cd accumulation than that of rice with high Cd accumulation,under different intercropping ratios,when the intercropping area ratio of rice varieties with low accumulation of Cd and rice varieties with high accumulation of Cd was 7:3,the overall decrease of Cd content in rice was the most ideal（25.4%and 32.3%,respectively）,and the significant yield of rice varieties with low accumulation of Cd was guaranteed(7.50±0.70 t·hm^-2).Therefore,it is recommended that the rice varieties with low Cd accumulation and plants with high Cd accumulation should be intercropped at 7:3 area ratio.（5）Rice varieties with low Cd accumulation were interplanted with several kinds of Cd high accumulation aquatic plants,such as Yu zhenxiang,Typha orientalis Presl,water spinach,Iris wilsonii C.H.Wright,Thalia dealbata Fraser and Canna indica L at a ratio of 2:1.The Cd enrichment ability of rice varieties with low Cd accumulation could be maintained at a low level,and the Cd content of rice varieties with about 0.021±0.001 mg·kg^-1 was lower than the corresponding standard,and the rice yield could also be guaranteed.As a rice variety with high accumulation of Cd,the Cd concentration in the overground part of Yu zhenxiang was 0.17 mg·kg^-1,about 5 times that of Chang liangyou 722.Several aquatic plants except Yu zhenxiang all showed the characteristics of ultra-high accumulation of excessive absorption of Cd.The BCF of Cd on their overground part was between 6.8～19.7,and the content of Cd was between 2.97～8.53mg·kg^-1,which was more than 100 times that of Cd on the overground part under the same environmental conditions.Among them,Thalia dealbata Fraser and Canna indica L phytoremediation works best,with the advantages of biomass is big,the extraction efficiency of Cd in soil were higher in more than 3%,combined with its characteristics can grow together with the rice in the rice fields,sure can apply to the paddy soil heavy metal phytoremediation,conducive to achieve the goal of paddy soil repair while production.