Effects Of Different Passivator Materials On Cadmium Availability In Soil And Cadmium Uptake In Rice

Soil reaction in China showed a zonal pattern of "acid in the south and alkali in the north".Heavy metal pollution aggravates soil acidification,enlarges soil acidification area,and affects plant growth and development.And the heavy metal enrichment in the plant not only poses a threat to the plant,but also threatens human health through the food chain.As the heavy metal cadmium pollution is particularly prominent in Hunan province,it is particularly important to take necessary measures to reduce the bioavailability of soil cadmium.In many restoration methods,in situ passivation restoration has been widely used because of its wide popularization and low economic cost.This study investigates the changing rule of the effectiveness of soil cadmium and the cadmium absorption of rice,using different cadmium accumulation ability of early rice and late rice as experiment materials,set up blank control and four passivation agent,（S）,calcium sulphoaluminate calcium chloride calcium aluminate（L）,aluminum hydrotalcite,magnalium hydrotalcite（A）（B）,each hectare seems set two gradient 1500 kg and 3000 kg,Nine treatments（CK,S1,S2,L1,L2,A1,A2,B1 and B2）were formed and field tests were carried out in Huayuan Village,Yanxi Town,Liuyang City,Hunan Province from 2020 to 2021.The main results are as follows:1.The application of different passivation materials can increase the yield of rice to a certain extent,and the key reason is to increase the effective panicles per unit area and grains per panicle.Application of A1,B1,B2,L2,S1 and S2 increased the yield of Zhuliangyou819 by 10.92% to 65.31% compared with CK,and application of A2,B2,L2,S1 and S2 increased the yield of Luliangyou 996 by 4.22% to 12.66%.Application of L1,L2 and S2 could increase the yield of late rice varieties.Compared with CK,applying B1,B2 and S1 could increase effective panicle number of rice by 12.94%,17.65% and 21.18%,respectively.According to two years’ data,B1 and S2 treatments had the best yield increase effect for different varieties.2.The application of 4 different passivation materials can improve the p H value of soil to a certain extent.One day after the application of passivating agent,the p H values of A2,B2,L2 and S2 treatments increased by 0.82,0.49,0.47 and 0.97 units,respectively,compared with that of CK treatment without passivating agent.Application of A2,B2,L2 and S2 increased the p H value by 0.41,0.09,0.1 and 0.15 units,respectively,compared with application of A1,B1,L1 and S1.Comprehensive two-year data showed that application of S2 passivated material had an opposite change rule on soil p H value.3.The activation rates of soil CaCl₂-Cd and soil Cd by different passivators also showed a decreasing trend over time.Compared with the results of passivator application after 28 days of reaction,the activation rates of soil Cd among different treatments decreased significantly.Application of passivators B2,L2,S1 and S2 decreased by 36.09%,21.35%,13.27% and 9.73%,respectively.In conclusion,the application of B1 and B2 passivated materials has the best effect in reducing the bioavailability and soil activation rate of cadmium in soil.4.Different passivating materials applied to double cropping rice had a downward trend on cadmium content in each part of rice plant compared with that without using passivating material CK.In the heading stage of early rice,for Zhuliangyou 819,application of A2 could significantly reduce the cadmium content in roots and ears by 77.42% and 51.28%,respectively,compared with CK.For Luliangyou 996,application of various passive materials could significantly reduce the cadmium content in roots and leaves compared with CK.Significantly decreased by 21.95%-78.57% and 17.14%-86.36%,respectively（P<0.05）.The results showed that the effects of A1,L2 and S2 treatments on Cd content in different parts of rice plants were longer than those of other treatments.To sum up,the fixation effect of passivating materials for soil cadmium will be different due to the different types,dosage of passivating agents and soil properties.Therefore,in order to achieve sustainable cadmium reduction effect,S2（3000kg/hm2 calcium sulphoaluminate）treatment can be used to increase yield,B1 and B2（1500kg/hm2 magnesium aluminum hydrotalc,3000kg/hm2）treatment can be used to reduce the bioavailability of cadmium in soil and the activation rate of soil Cd.