Effects Of Manganese Application On Cadmium Transformation In Brown Soil And Uptake By Maize

Cadmium?Cd?pollution in farmland soils is becoming more and more serious in China with the increase of industrial“three wastes”emissions.Applying amendments to repair Cd-contaminated soils plays an impotant role in ensure the safe production of grain under the premise of maintaining the soil properties.Brown soil was used as the tested soil that polluted by different degrees of Cd?5.0 mg/kg and 10.0 mg/kg?.A pot experiment was conducted to assess the effects of low,medium and high contents of MnSO₄?20 mg/kg,200 mg/kg,2000mg/kg?on soil Cd fractions,maize growth and Cd uptake.Aimming to provide theoretical basis for repairing Cd contaminated soil and protecting maize production security.The main results are as follows:?1?Compared with no Mn treatment,adding low and medium Mn had not significantly affected the pH of Cd contaminated soil?5.0 mg/kg and 10.0 mg/kg?.The pH of soil treated with high Mn was decreased significantly.Soil cation exchange under the different treatments were significant increase.In Cd-contaminated soil?5.0 mg/kg?,exchangeable Cd content under the low,medium and high Mn treatments were decreased by 9.4%,6.29%and 4.75%,respectively.Soil residual Cd content under the low Mn treatment was increased by 12.14%.The effects of medium and high Mn treatments on residual Cd were not significant.Fe-Mn oxide bound Cd contents under the low,medium and high Mn treatments were increased by1.78%,5.21%and 7.97%.In Cd-contaminated soil?10.0 mg/kg?,exchangeable Cd content under the low,medium and low,medium and high Mn treatments were decreased by 30.81%,28.78%and 13.78%,respectively.Residual Cd contents under these treatments were increased by 25.07%,18.90%and 4.90%.Meanwhile,their organically bound Cd concerntrations were decreased by 0.51%,0.86%and 0.95%.?2?Maize root length,root surface area,root volume and root mean diameter under the low Mn treatment were significantly improved as compared to the no Mn treatment.Root length and surface area were improved under the medium Mn treatment in Cd-contaminated soil?5.0 mg/kg?,but the treatment had no significant effect on root volumeand mean diameter.Otherwise,it had no significant effect on the root morphological parameters in 10.0 mg/kg Cd contaminated soil.Maize root length,root surface area,root volume and root mean diameter planted in Cd-contaminated soil?5.0 mg/kg and 10.0 mg/kg?under the high Mn treatment were reduced,significantly.The cumulative maize biomass under the low and medium Mn were higher than the check.Among the different treatments,maize biomass and yield under the low Mn treatment were the highest.?3?Cd enrichment factor of maize root,stem,leaves and grain under the low and medium Mn were significant reduced.Adding high content of Mn could increased Cd enrichment factor of maize root and stem,while decreasing the factor of leaves and grain.In Cd contaminated soil?5.0 mg/kg?,Cd content of grain under the low,medium and high Mn were decreased by 53.85%,48.72%and 46.15%In Cd-contaminated soil?10.0 mg/kg?,Cd content of grain under the low,medium and high Mn were decreased by 50.00%,52.33%and38.37%,respectively.?4?In Cd contaminated soil?5.0 mg/kg?,adding low concerntration of Mn could improve the proportion of Cd in cell wall of various maize tissues and reduced the propotion of Cd in organelles.In Cd contaminated soil?10.0 mg/kg?,the proportion of Cd in cell wall of maize root,leaves and grain under the medium Cn treatment were increased.Adding low Mn significantly improved the proportion of Cd in cell wall of maize stem,and reduced the proportion of Cd in organelles.?5?In Cd contaminated soil?5.0 mg/kg and 10.0 mg/kg?,photosysthesis under the low and medium Mn treatments were improved,while the high Mn contents might inhibit the photosysthesis.Considering the economic cost and Cd uptake by maize,20 mg/kg Mn content is recommended as a better amendment.