| Based on the current severe facts about the cadmium（Cd）contaminated farmland and the requirement for the safe utilization of contaminated farmland of the“Action Plan for Prevention and Control of Soil Pollution”,this article mainly focused on mild and moderate cadmium contaminated farmland soil.It took the soil cadmium passivation material as the research object,the in-situ immobilization remediation technology as the core,through indoor soil cultivation test,pot experiment of rice and field experiment,etc.to carry out the selection of the composition from the single passivation material to the combination of the passivation materials and optimize the optimal configuration of the combination of the passivation materials composition;used the passivation material screened in the previous pot experiment to implement the field in-situ immobilization plot experiment in 2018-2019 for 2 consecutive years in order to explore the passivation rate of 3 combinations of passivators and 3 kinds of single-passivators on mild to moderate Cd contaminated farmland soil,the rate of cadmium reduction in rice,and the stability of the passivation effect.Besides,this dissertation also explored the effect of passivators on soil fertility and the environmental health quality.Finally,the pot experiment of rice was used to verify the cadmium passivation effect,rice cadmium reduction rate and applicability of three combinations of passivators in different Cd contaminated farmland soils.The main conclusions were shown as follows:（1）After conducting indoor soil cultivation experiment to test cadmium passivation effect of nine single-passivators in two moderately Cd-contaminated farm soils,the results showed that the application of passivators（except for wormcast organic fertilizer and bamboo powder）increased the soil p H and reduced the availability of Cd content in the soil.For the passivation effect of cadmium,it mainly showed lime>sepiolite≥calcium magnesium phosphate>bone meal≥potassium dihydrogen phosphate>biochar>zeolite.In addition,the passivation effect of high volume application（0.30%of dry soil weight）was obviously better than that of low volume application（0.15%of dry soil weight）.By combining 7materials including lime,sepiolite,calcium-magnesium phosphate fertilizer,bone meal,potassium dihydrogen phosphate,biochar and zinc sulfate,and analyzing the range and variance of the 7-factor 2-level orthogonal experiments,it showed that the combined passivators of mixing 4 materials of lime,sepiolite,calcium-magnesium phosphate,bone meal had the best effect on increasing soil p H and reducing available Cd content in soil.（2）Through 4-factor 3-level orthogonal experiments on greenhouse rice pot experiment,lime,sepiolite,calcium-magnesium phosphate and bone meal were combined and applied in different proportions to three types of moderate Cd contaminated soils.The best ratio of combined passivators to reduce Cd in Shankeng diluvial gritty loamy paddy soil planting Yongyou 538 is sepiolite 50%,calcium magnesium phosphate 10%,bone meal 10%and lime 20%,among which the most effective composition is sepiolite;for Mukeng paddy field on desalting clayey polder planting Yongyou 538,the optimal ratio of combined passivators to reduce Cd of rice is sepiolite 50%,lime 40%,calcium magnesium phosphate 10%and Bone meal 10%,the components with significant effects are sepiolite and lime;Mukeng diluvial gritty loamy paddy soil where Yongyou 17 is planted,the optimal ratio of combined passivators to reduce Cd of rice is lime 40%and sepiolite 40%,bone meal 10%and calcium magnesium phosphate 10%,of which the significant components are lime and sepiolite.（3）After the field plot trials in 2018-2019 for 2 consecutive years,results showed that the application of 6 types of passivators in 2018 obviously reduced the Cd content of Yongyou 17 and Yongyou 538 rice,which were lower than the national standard of cadmium in food safety of which the value was below 0.2 mg kg-1.In 2019,using the same kind of passivator,and the Cd content of Yongyou 17 and Xiushui 134 rice was still significantly lower than that of the control.Among the treatments where no passivator was applied,sepiolite and combined passivator 1（lime 40%,sepiolite 40%,bone meal 10%and calcium magnesium phosphate 10%）had the best stability in the reduction of Cd in brown rice,and the passivation effect was sustainable for 2 years basically.From the perspective of rice Cd reduction rate and the impact on rice yield,Yongyou 17 was superior to the other two rice types.The field plot experiments in2018 indicated that by applying sepiolite and combined passivator 1,the soil p H of the rice at the mature stage increased to 0.73 and 1.40 units,and the passivation rates of available Cd in the soil were 32%and 51%,respectively,which were better than other treatments.Application of combined passivator 3（lime 20%,sepiolite 50%,bone meal 15%and calcium magnesium phosphate 15%）can significantly increase the content of soil available phosphorus.Application of combined passivator 1significantly increased soil catalase activity.The application of sepiolite and the combined passivator 1 significantly reduced the abundance of cad A functional genes in the soil at the booting period of rice,which increased the relative abundance of Bacteroides in soil bacteria by 1.7%and 2.6%,while the relative abundance of Cyanobacteria decreased by 4.7%and 5.1%.The soil under sepiolite and combined passivator 1 has similar bacterial community composition,which was different from that under other treatments.Soil p H,available Cd and soil available phosphorus content are strongly related to the bacterial community composition.（4）Choosing 3 different mild and moderate cadmium contaminated soils for the greenhouse pot experiment on validating the rice cadmium reduction effect.The results indicated that a combination of lime,sepiolite,bone meal and calcium magnesium phosphate has obvious passivation remediation effect and strong applicability to mild and moderate acidic Cd contaminated farmland soil.By using sepiolite consistent with the field test and three combinations of passivators showed that all four kinds of passivators can significantly increase the p H of the three soils,reduce the available Cd content in the soil,and highly reduce the Cd content in Yongyou 17.The best combination for reducing the Cd of brown rice in the soil of Cifeimiao silt-clayey yellow mottled paddy soil on fluvimarine deposit and Xiazhou blue clayey paddy soil is the mixed passivator 3,and the best combination for reducing the Cd of rice and brown rice in the soil of Shankeng diluvial gritty loamy paddy soil is the mixed passivator 1.Therefore,the optimal combination of passivators should take the soil type,physical and chemical properties of the soil and the degree of soil pollution into consideration. |
