| In order to compare the effects of different crop multiple cropping systems on the heavy metal content in paddy soil and rice absorption in southern China,and to explore the best way to reduce cadmium multiple cropping system,in 2016-2018,in Yueyang(experimental base of Municipal Institute of Agricultural Sciences)and Hengyang(experimental base of Municipal Institute of Agricultural Sciences)in Northern Hunan,Xiangyou 1035 seedlings were selected as the two cropping systems In the experiment,zhongzao39(the same as early rice and late rice)was used as the experimental material to carry out the three-year orientation experiment of crop multi cropping cultivation.The differences of heavy metal absorption,heavy metal content and p H value of rice soil were compared among five multi cropping systems,i.e.rice oil,rice oil,rice fertilizer,rice slack and rice oil no tillage.The main results are as follows:1.Compared with rice slack,the difference of rice fertilizer and rice oil is significant Rice oil was the best in increasing early rice yield,while rice fertilizer was the best in increasing late rice yield.In the same region,there are differences in the actual yield and biomass of the same season rice under the three treatments of rice fertilizer,rice slack and rice oil.The difference of the actual yield of Hengyang early rice and late rice under the three treatments is 12.75% ～ 19.24%,while that of Yueyang early rice and late rice under the three treatments is 2.36% ～ 15.53%.2.In different cropping systems of double cropping rice(rice slack,rice oil and rice fertilizer),the cadmium content of rice in all treatments increased first and then decreased.In the early rice of the two places,planting rape decreased the most,followed by green manure,and winter fallow was the least.And with the increase of planting years,the decreasing range has an increasing trend.The regularity of late rice was consistent with that of early rice.In2018,the cadmium content in rice straw,grain and grain of Hengyang early rice decreased significantly compared with that of the previous year,and the cadmium content in rice slack,rice oil and rice fertilizer rice straw decreased by 64.03%,68.97% and 73.11% respectively;the cadmium content in rice slack,rice oil and rice fertilizer grain decreased by 41.51%,55.56% and 55.17% respectively;the cadmium content in rice slack,rice oil and rice fertilizer grain decreased by 41.51%,55.56% and 55.17% respectively The decrease rate was60.38%,76.47% and 60.53% respectively.Compared with the previous year,the content of cadmium in rice straw,grain and pitfall grain of Yueyang early rice also began to decrease,with the decrease range of 36.76%,46.67% and 49.09% for each treatment,37.50%,46.15%and 40% for each treatment,and 39.29%,23.08% and 29.41% for each treatment.Compared with planting green manure or rape in winter,winter fallow can reduce arsenic content in rice plants,and with the increase of planting years,the decrease range has an increasing trend.Rice fertilizer can increase the accumulation of lead in rice grain.3.The effects of different crop multiple cropping systems on heavy metals uptake by rice plants under no tillage conditions were studied.However,the arsenic content was opposite to the cadmium content.The arsenic content in the rice plants under the rice oil treatment was higher than that under the no tillage treatment.During 2016-2018,the cadmium content of Hengyang rice grain treated by oil free treatment was 74.07%,47.87%and 27.78% higher than that of rice oil treatment,respectively.The cadmium content of Yueyang rice grain treated by oil free treatment was 25%,42.86% and 20% higher than that of rice oil treatment,and the same was true for rice straw and chaff grain.From 2016 to 2018,the arsenic content of Hengyang rice grains treated with oil free treatment was 21.21%,8%and 15.22% higher than that of rice grains treated with oil free treatment.The arsenic content of Yueyang rice grains treated with oil free treatment was 6.25%,7.35% and 21.9% higher than that of rice grains treated with oil free treatment,respectively.The same is true of rice straw and pitiful grain.However,no tillage with rice oil and rice oil had no obvious regularity to lead accumulation in rice.4.With the extension of planting years,rice fertilizer,rice slack and rice oil treatment in Hengyang and Yueyang will significantly increase soil p H.Compared with the first year of planting,the increase range of soil p H after three years was between 4.50% and 10.33%.In Hengyang area,the content of available cadmium in soil increased first and then decreased,but did not reach the significant difference level;the content of available lead in soil changed little in the early stage,but increased significantly by 12.66-38.61% in the third year of planting.This may be caused by exogenous pollution in the third year of planting in Hengyang area.In Yueyang area,the available cadmium content of each treatment increased first and then decreased.Compared with the second year of planting,the available CD content of each treatment decreased by 12.60-38.12% after three years,among which the available CD content of rice fertilizer and rice oil was lower than that of rice free treatment.The content of available lead in the soil of rice and rice fertilizer increased year by year,and the increasing range was 5.39% and 7.52% respectively.The soil available lead content of rice oil and rice oil increased first and then decreased,and rice oil treatment decreased 6.7%in the third year compared with the previous year. |
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