Study On Cadmium And Lead In Farmland Soil By Passivation Of Shell Powder With Different Particle Size

At present,the pollution of heavy metals Cd and Pb in farmland is becoming more and more serious in China,which has directly threatened human health.At the same time,a large number of discarded shells will be produced every year,resulting in increasingly prominent environmental problems.Because shell powder has strong adsorption for heavy metals such as Cd and Pb,it is of great practical significance to explore how to use shell powder to repair farmland polluted by heavy metals such as Cd and Pb.In this study,rice soil was selected as the research object,and shell powder with 10-mesh,60-mesh and 200-mesh sieve was used as the research material.Study on the passivation effect of different size shell powder on Cd and Pb by indoor culture.The effect of shell powder with different particle size and its combination with foliar barrier?spraying selenium fertilizer and silicon fertilizer?on Cd accumulation in rice was studied by field plot experiment.It provides scientific basis for effective utilization of shell powder and safe production of rice.The main research results are as follows:?1?The results of indoor culture showed that adding 1%?mass percentage?of shell powder with different particle sizes increased the p H value and organic matter content of soil to different degrees,and reduced the bioavailability of Cd and Pb in soil.Among them,the p H value of the soil treated with 10 mesh?BK10?,60 mesh?BK60?and 200 mesh?BK200?sieve powder increased by 0.4,0.6 and0.8 units,and the soil organic matter content increased by 2.50%,3.19%and12.28%,respectively.The passivation effect of shell powder on Cd and Pb increased with the decrease of particle size,and the available Cd and Pb contents in the soil treated with BK200 with the best effect decreased by 19.05%and45.25%,respectively.?2?The results of field plot experiments showed that shell powder of 3000kg·hm^-2 with different particle sizes could increase rice yield to some extent,but the difference was not significant,and the content of Cd and Pb in rice grains was also reduced.Among them,the BKF200 treatment with the smallest particle size had the best effect on reducing the contents of Cd and Pb in rice grains,which were reduced by 50.71%and 34.55%,respectively.The second treatment was BKF60,and the content of Cd and Pb in rice grains decreased by 34.43%and30.71%,respectively.The decrease of Cd and Pb contents in rice grains by different size of shell powder was mainly due to the increase of soil p H value and organic matter content,and the decrease of available Cd and Pb contents in soil.The smaller the particle size,the better the effect.Among them,the p H value of soil treated with BKF200with the smallest particle size increased by 1.44 units,the organic matter content increased by 7.77%,and the effective Cd and Pb contents decreased by 17.50%and 25.95%respectively.It can be seen that the smaller the particle size of the shell powder is,the more effectively it can improve the soil p H value and organic matter content,reduce the contents of Cd and Pb in the soil,and thus weaken the accumulation of Cd and Pb in rice.?3?The results of field plot experiment also showed that selenium fertilizer?Se?and silicon fertilizer?Si?spraying on leaf surface alone reduced the content of Cd in various tissues of rice,among which the content of Cd in straw,husk and grain treated with Si spraying on leaf surface alone decreased by 27.18%,38.95%and 18.28%respectively,and the effect of reducing Cd was better than that of Se fertilizer spraying on leaf surface alone.Base application of 3000 kg·hm^-2 over 10target shell powder?Se BKF10,Si BKF10?combined with foliage spraying of Se and Si rice showed more obvious Cd reduction effect.Among them,Si BKF10treatment had significantly lower Cd content in rice straw,rice husk and grains than Se BKF10 treatment,with a decrease of 48.39%,52.34%and 63.69%,respectively.In summary,the shell powder with small particle size can more effectively improve the soil p H value and organic matter content,and reduce the contents of Cd and Pb in available soil state and Cd and Pb in various tissues of rice.In addition,the Cd content of the above-ground tissues of rice could be further reduced by the combination of shell powder passivation and leaf barrier.It can be seen that reducing the size of shell powder and using it in combination with the barrier measures are more conducive to the rational utilization of shell powder and the safe production of rice.