Study On Agronomic Regulation Technology Of Moderate Cd Pollution In Farmland

Heavy metal pollution in soil has seriously threatened national health and food security.China’s farmland soil exceeds the standard rate of nearly 20%.Most of them are mild heavy metal pollution,Without changing the planting patterns and species,there are two economically effective ways for current moderately mild heavy metal contaminated soil.The first one is screening low accumulation heavy metal crops,by monitoring the concentration of heavy metals in edible parts of crops to achieve the purpose of safe and economical use.The second one is using soil heavy metal passivation agent to reduce the content of available heavy metal to achieve the purpose of reducing the absorption of heavy metals by crops.Through the above two methods,the concentration of heavy metals in the edible parts of crops can be reduced effectively,and the relevant national food hygiene requirements can be met.The study consists of three parts.In the first part,heavy metal low accumulation rice variety test shave analyzed the production of different rice varieties,heavy metal content in different parts of rice comprehensively,then screening rice varieties with low accumulation of heavy metals.In the second part,soil heavy metal passionate tests,which have compared five different deactivators with the blank controls,have measured the pros and cons of the treatment effect by soil pH,available heavy metals,and rice heavy metal concentrations,etc.,so as to screen out suitable soil heavy metal deactivators.In the third part,The effects of black-net coverage,black-film coverage and control（CK）without coverage on weed control were studied in order to reduce the labor cost.The rate of weed control,crop yield,Cd/Zn contents in crops were measured.The experiments in field were conducted with Cd-contaminated soil.The main results and conclusions of this paper are as follows:（1）Early rice varieties screening tests results show that there are significant differences in grain yield among different varieties.Hybrid rice CLY,the highest average yield of 678.1kg/mu.There is no significant differences in yield between different varieties of late rice.（2）In the field of soil that is close to being exceeded.Variety screening test shows that there was no significant difference in the Cd concentration of early rice.The rice with higher mean Cd concentration is LSZ,The YLY and ZZX rice have lower Cd concentration.There is a significant difference in Cd concentration in late rice.The species of rice with the highest Cd is HXN with an average value of 0.0707 mg/kg.Comprehensive comparison of rice Cd concentration and rice yield,it is confirmed that YLY is a high-yield and Cd low accumulation variety.（3）Soil heavy metal passivation screening test shows that Mineral passivator-DHJ will significantly change soil pH,soil organic matter and available soil heavy metal concentration after input.Other deactivators have no significant effect.Different extractant tests show that the test plot soil is more suitable to use CaCl₂ than DTPA as extractant to measure the soil available heavy metal concentration.（4）There is no significant difference in the rice yield of the early-late rice test and the heavy metal Cd content in rice.The concentration of Cd in early rice is lower after GF-treated,but the lowest concentration of late rice is JGZHF treatment.（5）Planting Sedum alfredii Hance in field plots,the rates of weed control by black-net coverage were 93.08%,93.12%and 77.99%respectively for 3 periods,while that by black-film coverage were 100%,98.39%and 87.39%,meaning both methods control well the weeds.In the second experiment planting low-Cd corn,the obtained results were rather similar.（6）The nutrient（nitrogen,phosphorus and potassium）concentrations in runoff water following the additional chemical fertilization after the corn flowering in the treatment of black-net coverage were lower than that of black-film coverage,and similar to CK.Hence,black-net coverage could not only effectively control weeds,but also have advantages of permeating the pass of rain-water and no need to open the nets during chemical fertilization.This method is particularly suitable to be applied in phytoremediation of Cd-contaminated soils.