Effect Of Organic Materials On Fractions Of Organic Matter And Cadmium Uptake By Rice In Paddy Soil

The effect of organic matter on the chemical behavior of heavy metals in soil is both related to its content and fractions.Dissolved organic matter(DOM)refers to the organic carbon dissolved in the soil solution,including the organic matters of different structures and molecular weight,such as soluble sugars,hydrocarbons,amino acids,fatty acids,humus and so on.Particulate organic matter(POM)is the active intermediate of the transformation of animal and plant residues into soil humus,which refers to the light organic matter with the particle size above 0.053 mm.Due to its unique high activity,DOM acts as the migration carrier of pollutant especially heavy metal in the soil,thus affecting the environmental behavior of heavy metals.DOM.POM has a strong ability to enrich heavy metals.The two organic matters on the impact of heavy metal activity is very different.The effect of the two on on the migration and transformation of cadmium(Cd)and Cd uptake by rice in paddy soil remains to be studied.In this study,a soil culture experiment applied biochar(BC),peat(PT),humus(HS),cow manure residue(CM),pig manure residue(PM),farm manure(FM)and domestic waste compost(DRC)was utilized to study the effects on the soil organic matter components DOM and POM and its dynamic relationship with the change of cadmium availability in paddy soil under the conditions of flooding.A pot experiment was conducted to study the effects of different organic materials on soil organic matter composition and Cd uptake of rice,explored the relationship between the two,so as to provide a basis for clarifying the interaction mechanism between organic matter and cadmium in paddy soil,and for rational selection of organic materials to amend Cd-contaminated paddy soil.The main conclusions are as follows:(1)Organic materials promoted mineralization of soil organic carbon.The cumulative mineralization of each treated soil showed CM> PM> FM> DRC> BC> PT> HS,CM,PM and FM are easier to mineralize than BC,PT,HS.(2)The organic material increased the pH of the paddy soil solution,the BC treatment was the highest,the PT treatment was the lowest,and the differences among treatments were significant.(3)In addition to BC treatment of DOC reduction,the organic material increased the SOC and POM content,POM-C and DOC content of the paddy soil.PT and BC treatments were the highest in terms of SOC content,which is related to the organic carbon content of organic materials.FM and CM treatments were the highest of DOC concentration in soil solution,related to the difficulty of decomposition of organic materials.HS treatment was the highest in POM-C content,and BC and HS treatments were the largest in POM content and contribution to soil carbon,which is related to the composition of organic materials and organic carbon content.(4)The effect of organic materials on soil POM-Cd content and soil water-soluble Cd in soil-rice system varies with material type,and the soil water-soluble Cd concentration in culture experiment is also improved.The Cd contents of the exchanged and bounds of Fe and Mn in the paddy soil increased,and the contents of carbonate bound,organic and residual Cd were decreased,indicating that organic matters promoted the activation of Cd in paddy soil.(5)The effects of organic materials on the biomass of rice roots,stems and leaves and brown rice vary depending on the type of organic material.FM and DRC treatments reduced the biomass of roots and stems and leaves of rice,and the remaining treatments increased the biomass of rice roots,stems and brown rice to different degrees.PT treatment was the largest to the increase of root,BC the largest to the stems and brown,and the increase rates were 68.59%,43.39% and 60.24% respectively.(6)Organic materials promoted the absorption of Cd in roots and stems and leaves of rice.PT and HS had no significant effect on Cd concentration in brown rice,but inhibited the transfer of Cd from stem to brown rice.The rest of the organic materials significantly promoted the absorption and transfer of Cd by brown rice.The correlation analysis showed that there was no significant correlation between Cd content in rice and soil DOC,POM and Cd content,but Cd content in roots was positively correlated with exchangeable Cd content in paddy soil,and was significantly negatively correlated with carbonate-bound and residual correlation,indicating that the organic materials promoted the uptake of Cd by rice by changing the forms of Cd.