Effects Of Soil Conditioner On Cadmium Accumulation And Its Synergistic Effect With Foliar Inhibitors In Double-cropping Rice

In order to find out the suitable soil conditioner and its synergistic effect with foliar inhibitor in double cropping paddy fields with mild cadmium pollution in southern Hunan,field experiments were carried out in Hengyang county from 2020 to 2021 to comparatively study the effects of three kinds of soil conditioner(biochar,quicklime and Xiangrunbang conditioner)applied in early rice season on the yield and cadmium accumulation and distribution of double cropping rice,and the synergistic effects of soil conditioner and foliar inhibitorwith early rice varieties Zhuliangyou 819 and Lulianyou 996,late rice varieties Xiangwanxian No.13 and Yuzhenxiang as materials and no soil conditioner as control.The main results are as follows:(1)Different soil conditioners had different effects on yield of double cropping rice.Biochar had a significant yield increasing effect,which could increase rice yield by6.67%-13.5%,and the main reason for yield increasing was to increase number of grains per panicle of rice,while quicklime and Xiangrunbang conditioner had no significant effect on the yield.(2)Soil conditioner could reduce the content of available cadmium in soil,and quicklime treatment had the largest decline,Xiangrunbang conditioner was the second,and biochar was the smallest.Biochar could only reduce the content of soil available cadmium in a short time after being applied to the soil in early rice season,but it had no obvious effect on late rice season,while the application of quicklime and Xiangrunbang conditioner could significantly reduce the content of soil available cadmium in early season and late season,but the decrease was greater in the early rice season.(3)The three soil conditioners had significant effects on the cadmium content in all stages and organs of double cropping rice.Quicklime and Xiangrunbang conditioner could significantly reduce the cadmium content in roots,stems,leaves and panicles,and the cadmium reduction rate was greater than that of biochar,while the cadmium reduction effect of biochar was mainly reflected in the stems,leaves and panicles,and the performance of each trend was basically the same in the two years.(4)The range of cadmium reduction of biochar on each variety was not large,but the cadmium reduction effects of quicklime and Xiangrunbang conditioner were obvious among varieties.The range of cadmium reduction of both on Lulianyou 996 and Yuzhenxiang was larger,while the range of cadmium reduction on Zhuliangyou 819 and Xiangwanxian No.13 was smaller.Taking the content of cadmium in brown rice as an example,quicklime and Xiangrunbang conditioner reduced the content of cadmium in brown rice of Lulianyou 996 by 23.11%-32.44%,Yuzhenxiang by 23.08%-26.45%,Zhuliangyou 819 by 14.56%-21.43%,and Xiangwanxian No.13 by 14.29%-17.20%.(5)The effect of foliar inhibitor on reducing cadmium in rice was related to variety characteristics.It had little effect on cadmium content in various organs of low cadmium accumulation varieties Zhuliangyou 819 and Xiangwanxian No.13,while it could significantly increase root-stem,root-leaf cadmium transfer coefficient and significantly reduce root-panicle cadmium transfer coefficient,so as to reduce cadmium content in brown rice of high cadmium accumulation varieties Luliangyou 996 and Yuzhenxiang by9.0%-15.2%.(6)The synergistic effect of foliar inhibitor and quicklime and Xiangrunbang conditioner on cadmium reduction of four varieties was not significant,and it had synergistic cadmium reduction effect with biochar on Luliangyou 996 and Yuzhenxiang,which could further reduce the cadmium content of brown rice by 9.2%-15.4%,but had no significant effect on the other two varieties.The synergistic cadmium reduction effect of biochar and foliar inhibitors was achieved by significantly reducing the migration of cadmium from stems and leaves to panicles.In conclusion,biochar is the best for yield-increasing of double cropping rice,while quicklime and Xiangrunbang conditioner are the best for cadmium reduction,and their cadmium reduction rangeis large for high cadmium accumulation varieties.Foliar inhibitors and their combined application with biochar have a better cadmium reducing effect on varieties with high cadmium accumulation.According to the comprehensive yield and cadmium content of brown rice,it is more appropriate to use biochar as conditioner in cadmium slightly polluted paddy fields in southern Hunan.If it is a variety with high cadmium accumulation,it is appropriate to adopt biochar + foliar inhibitor.