| In the context of the new era,China’s traditional industrialization process has entered a new path of transformation and upgrading,and the reduction and efficiency of chemical fertilizers and pesticides are also continuously promoting the green development of agriculture,but the problem of cadmium contamination of agricultural soil caused by the industrialization development and improper use of agricultural inputs in the past decades is still very prominent,which seriously threatens China’s food security production,and the existence of large areas of cadmium-contaminated farmland also urgently requires measures.The oilseed rape and rice rotation pattern is a green and efficient production model of grain and oil that effectively utilizes winter idle fields and promotes year-round yield and income,but existing studies have concluded that the rape-rice rotation model increases the risk of cadmium contamination in rice and is not suitable for application in cadmium-contaminated farmland.Based on this,the present study was conducted by selecting the high Cd accumulation oilseed rape variety"HI98",the low Cd accumulation oilseed rape variety"YG2009"and the low Cd accumulation rice variety"XZX45",the main rice variety"YLYSM"in the experimental area for crop rotation and the cultivation of"XZX45"and"YLYSM"after the abandonment of farmland.On the basis of these two models,we conducted a study on the safe utilization of cadmium-contaminated farmland,and carried out the verification of the effect of joint regulation technology for safe utilization,and investigated the effect and mechanism of cadmium migration and transformation under the oilseed rape and rice rotation pattern:(1)In a comprehensive view,the cadmium content of bolt and oilseed rape in HJ98 was significantly higher than that in YG2009 during the oilseed rape season.cadmium content of rice in the oilseed rape and rice rotation pattern was significantly lower(p<0.05),with the lowest cadmium content of 0.227 mg/kg in rice in the rotation between HJ98 and XZX45,but it still failed to fully achieve the standard production of rice in cadmium-contaminated farmland.In the oilseed rape season,the cadmium content of rapeseed and bolt in HJ98was significantly higher by 64.91%～109.74%and 111.78%～136.36%compared to YG2009.Compared with the overgrown and rice model,the oilseed rape and rice rotation pattern increased rice yield by 2.36%to 28.69%and stalk biomass by10.39%to 22.46%.The cadmium content of rice was significantly reduced by7.69%～20.16%,but all were higher than the national standard for food safety(0.20mg/kg).The total cadmium accumulation in the crop of oilseed rape and rice rotation pattern was higher than that of overgrown and rice model by 12.54%～54.75%and was able to reach 40.3 g/hm~2.(2)Random forest and structural equation modeling revealed that the cadmium content of rapeseed and rice was dominated by the cadmium uptake and accumulation characteristics of the crop,with differences in the effects of HJ98 and YG2009 and XZX45 and YLYSM on the soil effective state cadmium and effective phosphorus content.In the oilseed rape and rice rotation pattern,the planting of oilseed rape was able to increase soil organic matter,effective cadmium and effective phosphorus content,and influenced soil available cadmium and available phosphate content in rice,thus reducing rice cadmium content.During the oilseed rape season,the organic matter and available cadmium content of inter-root soil of HJ98 were increased compared with YG2009,and the available phosphorus content of inter-root soil of both HJ98 and YG2009 were increased compared with throwing wasteland.At maturity,the available cadmium content of inter-root soil of HJ98 was significantly increased by 14.42%～18.94%and the effective phosphorus content of inter-root soil was significantly increased by43.63～50.6 mg/kg compared with YG2009.The increase of soil organic matter,available cadmium and available phosphorus content of oilseed rape could promote the accumulation of cadmium by oilseed rape.In the rice season,the available cadmium content of inter-root soil was reduced in XZX45 compared to YLYSM.The planting of HJ98 significantly reduced the Cd content in the inter-rhizosphere soil of XZX45 at the filling stage compared with YG2009.Planting HJ98 was able to increase the available phosphorus content of rice topsoil and inter-root soil compared to YG2009.In the overgrown and rice model,the available phosphorus content of the inter-root soil of XZX45 at the filling stage was significantly higher by 16.36 mg/kg compared with YLYSM.Thus,it can be seen that the effect of rice on the available cadmium and available phosphorus content of the soil differed between varieties,and planting HJ98 was effective in reducing the available cadmium and increasing the available phosphorus content of the soil of rice,thus reducing the cadmium content of rice.(3)In the oilseed rape and rice rotation pattern,the combined control technology was mainly used to reduce rice Cd content by increasing soil p H and reducing soil Cd in the effective state.In terms of rice Cd reduction,the best results were achieved by selecting HJ98 in rotation with XZX45 and combining foliar silica fertilizer and lime for control,with a significant reduction of 60.35%in rice Cd content of 0.09 mg/kg.In oilseed rape season,application of foliar selenium and silica fertilizers could increase oilseed rape yield and stalk biomass.Foliar silica fertilizer was able to increase cadmium content in oilseed rape and foliar selenium fertilizer was able to reduce cadmium content in oilseed rape.In the rice season,only the combination of silica fertilizer and weidikang in the combined control technology was able to significantly increase rice yield by 23.41%.The cadmium content of rice significantly decreased by 32.76%～60.35%after applying the combined regulation technology,and all of them could meet the limit standard(≤0.20 mg/kg).This was mainly because the combined control technology was able to significantly reduce the effective state Cd content of soil by 24.60%～85.04%and significantly increase the soil p H by 0.41～0.99,thus inhibiting the accumulation of Cd in rice. |
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