Effect Of Combined Application Of Cow Manure And Corn Straw On Cadmium Transformation In Brown Soil And Uptake By Corn

The problem of heavy metal cadmium pollution in agricultural soils in China is becoming more and more serious.Cadmium pollution in most farmlands is moderate or mild.It is impossible to withdraw these lands from farming or change the properties of land crops for the purpose of ensuring food production.Therefore,it is of practical significance to reclaim the Cd contaminated farmland.In this paper,pot experiment was used to study the effect of combined application of cow manure and corn straw on cadmium transformation in brown soil and uptake by maize.The soil pH,organic matter content and cation exchange capacity were measured to reveal the mechanisms of cadmium transformation.Cadmium content in maize roots,stems,leaves,and grains were also measured to calculate the accumulation factor and translocation factor of cadmium in maize plants.The results are as follows:(1)Compared with no cow manure and straw addition,soil pH increased 0.36,0.17,and 0.16 units,respectively,for nitrogen ratio of cow manure to straw being 1:1,3:1,and 5:1,soil organic matter increased 1.11,1.07,and 1.00 g/kg and cation exchange capacity increased 1.11,0.65,and 0.50 cmol/kg.The treatment with a nitrogen ratio of cow manure to straw being 1:1 resulted in a significant increase in soil pH,organic matter and cation exchange capacity.(2)Compared with no cow manure and straw addition,the contents of the exchangeable fraction of cadmium decreased 0.65,0.53,and 0.38 mg/kg for the nitrogen ratio of cow manure to straw being 1:1,3:1,and 5:1,respectively.The organic bound form cadmium and residual cadmium extensively increased with the combined application of cow manure and straw.There was a significant negative correlation between the exchangeable Cd content and pH in soil,and there was a highly significant positive correlation between residual Cd content and pH.(3)Compared with no cow manure and straw addition,maize yield increased 72.41%,48.93% and 43.51% for the nitrogen ratio of cow manure to straw being 1:1,3:1,and 5:1,respectively,and the aboveground biomass increased 27.46%,18.11% and 15.05%,respectively.(4)Compared with no cow manure and straw addition,the uptake of cadmium by different parts of maize plant decreased for the combined application of cow manure and straw.Cadmium accumulated mainly in root,stem and leaf of maize plant,and cadmium content in grain reduced 80%?70% and 55% for the nitrogen ratio of cow manure to straw being 1:1,3:1,and 5:1,respectively.Thus,the combined application of nitrogen ratio of cow manure to straw being 1:1 should be considered a suitable soil amendment for cadmium.