The Effects Of Heavy Metal Content Between Paddy Soiland Rice In Rice-crayfish Coculture

In recent years,due to the excessive use of mining,chemical fertilizers and pesticides and sewage irrigation,the content of heavy metals in the environment has increased.In areas where the soil is polluted by heavy metals,the content of heavy metals in rice seriously exceeds the standard.The content and form of heavy metals in soil can be changed by changing rice planting mode;Rice-Crayfish Coculture System has changed the ecological process of paddy field,crayfish activities and breeding,field engineering and water,fertilizer and feed management,and has an impact on the soil environment,thus affecting the form and activity of heavy metals in paddy soil.In order to explore the difference characteristics of heavy metal contents in paddy soil and rice under Rice-Crayfish Coculture System,the content differences of heavy metals(Cr,As,Cd,Pb,Hg)in paddy soil and rice samples under Rice-Crayfish Coculture System and Rice Monoculture System were analyzed through the field experiment of Rice-Crayfish Coculture Systeml in different regions of Hubei Province in 2019(Qianjiang,Jianli,Jingmen,Xishui and Yangxin)and the fixed-point experiment in 2020(Jingmen,Jianli and Xishui),The results are as follows:(1)The Rice-Crayfish Coculture System had significant effects on the key physical and chemical factors of soil.Under the multi-year Rice-Crayfish Coculture System in different regions of Hubei Province,the soil organic matter content and cation exchange capacity of 0-20 cm and 20-40 cm were significantly higher than those of Rice Monoculture System in different periods,and the change of soil pH was inconsistent under different soil backgrounds.When the soil was weak alkaline soil,the pH of 0-20 cm soil in Rice-Crayfish Coculture System increased in different periods;When the soil was weak acid soil,the pH of 0-20 cm soil under Rice-Crayfish Coculture System decreased significantly in different periods.(2)The Rice-Crayfish Coculture System has an obvious influence on the heavy metal content in different soil layers.Before rice cultivation,the contents of Cr,Pb and Hg in the 0-20 cm soil of Rice-Crayfish Coculture System were significantly different with the Rice Monoculture System.When the soil is weakly alkaline,Cr,Pb and Hg in the soil decrease significantly,Cr,Pb and Hg increase significantly.After rice harvest,the content of Cd and Pb in 20-40 cm soil of Rice-Crayfish Coculture System was significantly lower than that of Rice Monoculture System.(3)Rice-Crayfish Coculture System had a significant effect on the content of heavy metals in rice plants.Compared with the Rice Monoculture System,the heavy metal content in rice roots,stems,leaves and ears in different regions of Hubei Province had no consistent change law,but the content of Cd and Pb in different varieties of rice brown rice decreased significantly.Among them,the content of Cd in Huanghuazhan and Yuzhixiang decreased by 56.0% and 52.5% on average,and the content of Pb in Xiangwanxian 12 decreased by 63.4% on average.When the soil background of Rice-Crayfish Coculture System was weak alkaline soil,the content of Cd in brown rice decreased and the content of as increased.Among them,Xiangwanxian 12 significantly increased by 89.4% and Huanghuazhan significantly increased by 47.6%.When the Rice-Crayfish Coculture System soil was weak acid soil,the contents of Cd,Pb and as in brown rice decreased at the same time.Among them,the contents of as in Xiangwanxian 12,Huanghuazhan and Yuzhixiang decreased significantly by 35.8%,34.6% and 33.3% respectively.(4)In the Rice-Crayfish Coculture System,the soil physical and chemical properties affecting the transfer of Cd ions from soil to brown rice are soil pH,cation exchange capacity and soil organic matter.Multiple regression analysis shows that cation exchange capacity is the most important factor,with a contribution rate of48.6%,and the secondary factor is soil organic matter,with a contribution rate of27.6%;The key factors affecting the transfer of Pb ions from soil to brown rice are the content of Pb in soil and soil organic matter,and the correlation coefficients are-0.568 and-0.407 respectively;The physical and chemical properties of soil affecting the transfer of as ions from soil to brown rice are soil pH,cation exchange capacity and soil organic matter.Multiple regression analysis shows that the content of soil organic matter is the most important factor,with a contribution rate of 66.9%,and the secondary factor is cation exchange capacity,with a contribution rate of 22.1%.In conclusion,the multi-year Rice-Crayfish Coculture System can significantly increase the content of soil organic matter and soil cation exchange capacity of0-20 cm and 20-40 cm,and the impact on soil pH is related to the pH value of soil background itself.The multi-year Rice-Crayfish Coculture System can significantly reduce the contents of Cd and Pb in brown rice of different rice varieties.Soil physicochemical factors affecting the transfer of Cd and As to brown rice are cation exchange capacity and soil organic matter.