| The study area of this thesis was Mosuowan irrigation area in Xinjiang,exploring influence of farming process in cotton field for heavy metals accumulation in soil by comparing with cotton soil and desert soil which were selected 5a,10 a,20a and 30 a by area survey analysis and the field orientation,and drawing the spatial distribution map of soil heavy metals by Geographic and Statistical Analysis in whole Mosuowan irrigation area,therefore,which supply foundation for cotton soil quality in Mosuowan irrigation area.Finally,selected Cr of this area heavier pollution was modified object,and studying influence of several kinds of chemical modifier for species distribution and transformation of Cr in soil by laboratory culture experiment,we conclude that:(1)The content of heavy metals(Cr,Ni,Cu,As,Pb)in cotton soil(0~100 cm)were 90.65,32.22,52.64,10.90 and 13.86 mg/kg,and desert soil were 78.21,32.34,44.16,9.48 and 13.91 mg/kg,the content of Cr,Ni,Cu and As in cotton soil were significantly greater than the desert soil,and all were higher than the soil background value in Xinjiang,the content of Pd was no significantly difference and was under the soil background value in Xinjiang.Variable coefficient of five kinds of heavy metals in cotton soil was all higher than the desert soil,which was medium variation.(2)For different profile distribution characteristics of cotton soil 5a,10 a,20a and 30 a,we find that because growth of succession cropping time,the content of heavy metals Cr,Ni,Cu,As and Pb were gradually elevated,and as the depth increased of soil,the content of heavy metals were gradually decreased.In the correlation analysis,it was found that the accumulation of Cr,Cu and As heavy metals in cotton soil was mainly caused by the application of phosphate fertilizer,and the correlation between heavy metal elements and N,P,K and pH in wasteland was not Significantly,it is further explained that heavy metals are accumulated in the process of continuous cropping of cotton fields.(3)Verified practicability of X-Ray Fluorescence Spectrometer by modeling inquiry and model validation,the R2 of model were 0.9124,0.8979,0.7723 and 0.8729 mg/kg,slope and intercept were optimized,were nearly ideal model,the testing result after calibrating were significantly positive correlated with ICP-AES test results with traditional laboratory.Proving practical applicability of PXRF and high accuracy of calibration curve by 36~50 soil sample formed verification model of second sampling.(4)The variation function of cotton surface layer soil of Mosuowan irrigation area were calculated and model-fitted by applying Geographic and Statistical Analysis,we discover: the exponential model of Cr and As were best,the Gaussian model of Ni and Pb were best,the spherical model of Cu was best,the nugget effect of Cr,Cu and Pb were 0.86,0.92,0.96,and spatial correlation is weak,it was greatly affected by artificial random factors,the nugget effect of Ni and As were 0.57,0.41,and spatial correlation of medium,it was affected between artificial random factors and spatial structure factor.Compared with background value of soil,the content of heavy metals show a rising trend in Mosuowan irrigation area,and the content totally show a decreasing tend from southeast to northwestern,this related with local tillage model and geographical feature of south is higher than that in north,which proving long term continuous cropping of local regional cotton could lead to accumulate of soil heavy metals.The current evaluation result in research area are Cr and As approaching the slight pollution levels,Ni can lead to slightly pollute for soil environment,so we should control Ni of heavy metals,and from now on,avoid influence of non-area factor,timely warning.(5)Studying remediation effectiveness of different mineral for soil heavy metal Cr by pot experiment,we find that ameliorant could control The amount of exchangeable state of Cr,but increase pH to some degree,with pollution concentration increased,its influence decreased,and higher than CK.Among four ameliorants,amendment effect of calcium magnesium phosphate fertilizer is best,the content of exchangeable state decreased firstly and increased subsequently,the content of residual increased at first and decreased subsequently,finally,the content of exchangeable state decreased.The amended effect of lime is lower than calcium magnesium phosphate fertilizer,it mainly transformed exchangeable to Iron manganese oxide combination patterns of Cr.The amendment effect of those ameliorants are significantly higher than the straw and the activated carbon,but the influence effect of Cr exchangeable state are short,the content of exchangeable state increase after 42 days.The activated carbon mainly transforms exchangeable state to organic combination state,and the content show a increase tend after 56 days,but the amendment effect is lower than calcium magnesium phosphate fertilizer and lime.The influence of the straw is non-significant for the content of exchangeable state,it related with the content of ameliorants and incubation time.In conclusion,the planting measures of long term continuous cropping of local regional cotton could lead to seriously accumulate of soil heavy metals,and mainly accumulate in surface soil.The cotton soil environment of total Mosuowan irrigation area belong to non-pollution area,but it is nearly light pollution levels,the future planting process should be pied attention to the prevention and control work of heavy metals pollution.Adding amendments to pollution soil of Cr,which could lead to increase of pH,with exchangeable state ranging,the final content would increase,thus,the bioavailability of Cr decreased in soil,and reached objective of amending Cr polluted soil. |
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