Targeted Acidity Regulation Of Polluted Acidic Paddy Soil And Its Cadmium Reduction Effect

The pollution problems of soil acidification of heavy metals such as cultivated land and cadmium in China are becoming increasingly prominent,and the safe utilization of land resources and the sustainable development of agricultural resources are facing major challenges.Soil acidification not only causes soil fertility decline,but also further enhances the activity of cadmium in soil and its migration to crops,and exacerbates the risk of cadmium exceeding the standard of agricultural products polluted by cultivated land.Therefore,it is urgent to control soil acidity and reduce the risk of heavy metal pollution such as cadmium.In order to reduce target cadmium regulating acid,this study will select 7rice soil developed from quaternary clay,granite weathering and plate shale to conduct soil training test and neutralization titration tests.In terms of the materials to adjust acid,the calcium oxide,calcium carbonate,sepiolite,biocarbon with calcium oxide and so on are applied to carry out continuous pot experiment.the results showed the acid regulation target together with its influencing factors,prediction model and cadmium reduction by targeted acid modulation to provide theoretical guidance and technical support for the safe utilization of polluted farmland resources in the south.the main results are as follows:（1）The results of soil culture and neutralization titration in 7 paddy fields showed that the soil DTPA-Cd and CaCl₂-Cd are decreased with the increase of soil pH and the inflection point appeared between pH 6.5and 7.5.And the targeted pH of cadmium regulating acid reduction of acidic paddy fields was 7.0.The relationship between soil pH and the amount of lime is logarithmic.Through stepwise regression analysis,this results showed the logarithmic function model parameters are affected by soil pH,organic matter,cation exchange capacity and so on,which will further help construct a mode to adjust acid and reduce cadmium in acid paddy soil.（2）Pot experiment on acid and cadmium reduction in paddy soils based on Quaternary laterite and granite weathering investigated the influence of targeted acid regulation and its application materials on soil cadmium activity.The results showed that:quantitative application of calcium oxide,sepiolite,calcium carbonate,and biochar combined with calcium oxide on rice will make the pH value of the two different soil-forming parent materials approached the target pH（7.0±0.29）on the30th day of growth.The increase of soil pH can effectively reduce the content of CaCl₂-Cd and DTPA-Cd in the two soils,and the content of CaCl₂-Cd and DTPA-Cd in the soil at different growth stages of rice decreases with the increase of soil pH.The effect of applying calcium carbonate and sepiolite in reducing cadmium is more significant.The content of CaCl₂-Cd in calcium carbonate treatment is reduced by64.92%～82.55%,the content of DTPA-Cd is reduced by 14.98%～30.50%;the content of CaCl₂-Cd in sepiolite treatment is reduced by63.32%～88.01%,the content of DTPA-Cd has decreased by17.62%～30.51%,There was a negative correlation between soil pH and the content of CaCl₂-Cd and DTPA-Cd.（3）Based on two experiments of targeted cadmium regulating acid reduction in rice soil,this study investigated the influence of targeted acid regulation and its application materials on soil cadmium morphology transformation.The results showed that the application of calcium oxide,calcium carbonate,seaweed stone and biocarbon could reduce the content of convertible cadmium and increase the content of cadmium carbonate,With good calcium carbonate treatment effect,The content of convertible cadmium in the soil decreased significantly by16.91%～32.52%,and that of cadmium in the carbonate binding state increased significantly by 29.02%～65.24%.The morphological distribution characteristics of the two soils in early and late rice were mainly residual slag state.The residual slag state>Fe-Mn oxide bound state>exchangeable state>organic matter bound state>carbonate bound state.（4）Based on two pot experiments of paddy soil targeted acid-regulating and cadmium-reducing,the effects of targeted acid-regulating and its application materials on cadmium absorption,transport and accumulation in rice were studied.The results showed that calcium oxide,calcium carbonate,sepiolite,biochar combined with calcium oxide and a small amount of biochar could effectively inhibit the absorption of cadmium in the roots,stems,leaves and rice of rice plants in early and late rice.the general rule of Cd transport coefficient in early and late rice plants is:TF _leaf/stem>TF _rice/leaf>TF _stem/root.All treatments reduced the concentration of Cd in the roots of rice plants and inhibited the transfer of Cd from roots to stems and leaves to rice,rice cadmium content eventually significantly decreased by 48.51%～92.02%,below international limited standards.The results showed that the targeted acid adjustment effectively inhibited soil acidification,alleviated the toxicity of soil heavy metal cadmium to rice,and was beneficial to the safe use of cultivated land resources and the safe production of agricultural products.