Effects Of Soil Fumigation On Speciation And Availability Of Trace Elements In Greenhouse Soil

With the rapid development of agricultural modernization facilities,expanding of crop cultivation area and increasing of grain yield in China,agricultural soil borne diseases and insect pests,nematodes and weeds have become more and more serious,which restricted the yield and quality of the harvest of agricultural production.Soil fumigation is the most comprehensive,effective and stable technology to prevent and control soil borne diseases and insect pests.It has been widely applied worldwide,and the range of application in China is also expanding.Chloropicrin(CP),1,3-dichloropropene(1,3-D),dazomet(DZ)and dimethyl disulfide(DMDS)are fumigants that have the best effects and the most extensive market applications.However,soil sterilization and fumigation could kill and inhibit a variety of microbial populations,thus changing the form of nitrogen and some trace elements in the soil.In order to further discover and analyze the effects of these fumigants on the availability,mobility and toxicity of soil nitrogen and trace elements,we used improved BCR three-step sequential extraction,DTPA extraction and other soil elements analysis methods.The purpose is to better evaluate the effect of several common fumigants on the soil environment and soil ecosystem,so as to provide the guidance of the actual agricultural production better.1.Effects of several fumigants on the sepciation of soil nitrogen and trace elementsThe results showed that chloropicrin(Pic),dimethyl disulphide(DMDS),1,3-Dichloropropene(1,3-D)and dazomet(DZ)fumigation could increase the content of ammonium nitrogen in soil by inhibiting the nitrification of the soil,and increased the total amount of inorganic nitrogen,which significantly activated the soil nitrogen in three different types of soil.After the soil fumigation with four fumigants,the increased amounts of ammonium nitrogen content can be arranged as follows: Pic>DZ>DMDS>1,3-D.Improved BCR three step sequential extraction was used to measure the changes of soil trace elements.The fumigation treatments with Pic,DZ and DMDS significantly increased the contents of exchangeable and carbonate bound of manganese(Mn)and cobalt(Co)in soils and significantly decreased the contents of Fe-Mn oxide bound of manganese,but the contents of soil trace elements in organic matter and sulfide bound were not changed.The contents of nickel(Ni)and copper(Cu)were changed differently with different treatments.And the speciation of other trace elements like iron(Fe),cadmium(Cd)and zinc(Zn)only has changed with some certain treatmen.Therefore,soil fumigation significantly increased the availability and mobility of manganese(Mn)and cobalt(Co)in soil.But there was no significant impact on other soil trace elements.Soil fumigation significantly increased the contents of available N,Mn and Co.And after the fumigation treatments with Pic,DZ and DMDS,The enhancement effect of available Mn and Co elements from strong to weak is DZ > Pic > DMDS.Several elements including N,Mn and Co in soil were activated,which may be an important factor for the strong growth and high yield of crops grown in soil after fumigation.2.Effects of chloropicrin fumigation on the dynamic changes of soil available trace elementsThe effects of chlorpicrin fumigation on soil microbial respiration and soil available trace elements were measured after three different concentrations of low dosage,standard dosage and high dosage of chlorpicrin fumigation in cultivated soil,which was to discover intensity and time about the effect of chloropicrin fumigation on available trace elements in soil.The results showed that the microorganisms were significantly killed and the respiration of microorganisms was inhibited in the soil after chlorpicrin fumigation.Due to the decrease of microorganism in soil and the active substances secreted by dead microorganism,the content of available Mn、Co、N and Cu elements in soil increased significantly after chlorpicrin fumigation.After fumigation,the soil microbes were recovered slowly after the fumigant was released,which also made the contents of several available microelements slowly recover.The content of available Mn,Co and Cu was not recovered to the same level as that of the control group until 4~5 weeks after fumigation,but available the content of available nickel has not recovered completely for 6 weeks.Therefore,in the case of the lack of these trace elements in the agricultural soil,microfertilizers containing Mn,Co and Cu elements should be properly added into soil at third,fourth and fifth weeks after chlorpicrin fumigation,so that the crops planted in the soil could grow healthily to achieve higher crop yields.At the same time,the experimental results showed that soil fumigation does not affect and change the soil microelement environment for a long time,and further proved ecological environment safety of chloropicrin fumigant.