Study On Effect Of Seasonal Substitutive Planting Of Maize To Rice In Paddy Field With Moderate Cadmiun Pollution

Today’s heavy metals"five drugs"(lead,chromium,arsenic,mercury,cadmium)are important pollutant in agricultural environments.In recent years,cadmium pollution in rice,especially in Hunan Province get much attention.This study was conducted paddy field with moderate cadmiun pollution in Yisuhe Town,Xiangtan County,Hunan Province.Through comparing the soil total cadmium and available cadmium dynamics,cadmium accumulation and distribution characteristics,crop yield and economic benefit in three planting systems(double cropping rice,spring maize-late rice,early rice-autumn maize)were discussed the feasibility,safety and economy of seasonal alternative planting of maize to early rice and late rice in paddy fiecd contaminated with moderate cadmiun pollution.In order to clear a suitable two-cropping alternative cropping pattern for double-cropping rice in paddy fiecd with moderate cadmium contaminated.The main results are as follows:1.In three planting systems,double cropping rice,spring maize-late rice and early rice-autumn maize,all crops could normally mature,so the three planting patterns were feasible in Hunan Province,Xiangtan area.2.Spring maize-late rice and early rice-autumn maize model could replace the double cropping rice model from the income of production,net income and income of single labor.3.The content of cadmium in various organs of rice increased with the growth process.The content of cadmium in brown rice reached 0.231-0.344mg/kg at maturity in 2015and the content of cadmium in brown rice reached 0.426-0.823mg/kg at maturity in 2016.The highest cadmium content in maize was the advancement of the grouth stage(five leaf stage),and the cadmium content in each organ showed a decreasing trend,and the content of cadmium in maize grain was in range of 0.036-0.081 mg/kg in 2016.Replancement of rice with maize could ensure the product cadmium content in agricultural to meet national quality standards.4.The effect of pre-season maize on reducing cadmium content in early rice in next year was not significant,but pre-season maize had a certain effect to reduce the cadmium content In late rice brown.The content of cadmium in brown rice in spring maize-late maize was 0.621mg/kg,which was 0.202mg/kg lower than that in double cropping rice,and the decreasing range was 24.54%.5.The total cadmium accumulation in mature period of late rice was higher than that in early rice,but the accumulation of cadmium in empty shell,empty grain and brown rice was lower than that of early rice.The accumulation of cadmium in various organs of rice increased gradually with the growth process,and the accumulation of cadmium of late rice in double cropping rice system was 46.541 g/hm~2,while accumulation of cadmium of late rice in spring maize-late rice system was 28.300g/hm~2 which indicated that pre-season maize had the effect of decreasing cadmium accumulation in late rice.In spring maize-late rice model,the cadmium content in maize was lower,the accumulation of cadmium in the shoots was higher than that of the early rice-autumn maize model,so replacement of the spring maize-late rice model to the double cropping rice pattern was more favorable for the remediation of cadmium contaminated paddy ficed and safety of agricultural products.6.The accumulation of cadmium trend in different crops was different.As for rice the accumulation of cadmium was little in the early stage of rice growth,and the accumulation of cadmium in the middle filling stage-maturity stage was the highest.As for spring maize and autumn maize cadmium accumulation were mainly occurred at sowing tobig flare stage.Effect of the pre-season maize on the accumulation of cadmium of early rice was not significant,but cadmium accumutation at the middle filling-maturity stage of late rice could be reduced,and the performance in 2016 was more obvious.7.The pre-season maize could decreased the available cadmium content at maturity stage of rice,while the available cadmium content at the maturity stage of maize was higher than that at the maturity stage of rice.8.The total cadmium content of soil did not change much in two years,but there was a significant difference in total cadmium content after planting maize.As for proportion of effective cadmium content to total cadmium contant at the maturity stage in the soil,the difference among treatments in the early season of 2015 was not significant,while the proportion of available cadmium in maize maturity period was significantly larger than that in the same period of rice,which indicated that cadmium in soil had been activated by paddy-upland rotation.In addition,in the moderate cadmium contaminated rice field,replacement double-cropping rice by spring maize-late rice and early rice-autumn maize model can not only maintain higher economic benefit but also ensure the cadmium content in agricultural products to meet the country quality standard,and the spring maize-late rice had more cadmium removal and had greater effect on soil remediation.