Effects Of Swine Manure Application On Heavy Metals In Soils And Crops Under Rice Wheat Rotation System

Under the rice wheat rotation,throughfield experiments and mathematical statisticsto explore the changes of heavy metals in soil and the content of heavy metals in the crop,the risk situation of safe agricultural production inretuming of swine manure has been proved.Nine treatments were designed includingcontrolno fertilizer(CK)5 chemical fertilizeronly(CF),straw with chemical fertilizer for the total amount of CF(SCF),20%N from swine manure540%N from swine manure,60%N from swine manure,80%N from swine manure,100%N from swine manure andl20%N from swine manure with the balance of equal nitrogen from adding chemical fertilizerfor field tests in 2 years.The crop and soil in the mature stage of wheat and rice in second years were studied to explore the contents of Cu,Cd,Pb and Zn in soil and the distribution of heavy metals in different organs of crops.The main research results were as follow:(1)The amount of Cu,Cd,Pb and Zn in the soil of wheat and rice increase with the increase of swine manure application.According to the Farmland Environmental Quality Evaluation Standards for Edible Agricultural Products(HJ/T332—2006),the content of heavy meatls in soil reach the Standards.The form of the Cu,Cd,Pb and Zn were mainly in the residual state,regardless of the wheat season or the rice season,and the residual state accounted for about 40% ?60% of the total.The weak acid extractable Cd was the second to the residue state in wheat season and rice season,which accounted about 16%-23% of the total amount.The results showed that the content of available Cd in soil was higher,and the potential pollution risk of Cd was higher.In the process of agricultural production,we should pay attention to the prevention and control of Cd pollution.Compared with control groups,the total Cu,Cd and Zn in the M6(17844kg hnr2)treatment of high amounts of swine manure were significantly higher than those of the control group.In addition to individual morphology,most form of the heavy metals in the M6 treatment was significantly higher than the control groups.The results showed that excessive application of swine manure could not only increase the total amount of heavy metals in the soil,but also lead to an increase in most of the morphological content.(2)The contents of Cu,Cd,Pb,Zn(root,stem,leaf,grain)in each organ of wheat,all showed Zn > Cu > Pb > Cd.The content of each kind heavy metals in different organs was different,the content of heavy metals Cu,Cd in different organs showed root > leaf > stem >grain;the Pb of contents in different organs showed root > stem > leaf > grain;the Zn of contents in different organs showed root > grain > leaf > stem.In each swine manure treatment,the low amount of swine manure Ml,M2(2794?5948 kg hnr2)compared with chemical fertilizer treatment CF can significantly reduce the content of heavy metals in different organs of wheat.The contents of heavy metals Cu,Cd,Pb and Zn in the roots,stems,leaves and grains of rice all showed Zn > Cu > Pb > Cd.The content of each kind heavy metals in different organs was different,The contents of Cu in different organs showed root > stem > seed >leaves;The contents of Cd in different organs showed leaf > root > stem > grain;The contents of Pb,Zn in different organs showed root > stem > leaf > grain.Under every swine manure treatment,the low amount of swine manure Ml could reduce the content of heavy metals in rice organs compared with the chemical fertilizer treatment CF.(3)In wheat and rice seasons,the linear regression analysis between the amount of swine manure and the heavy metals of Cu,Cd,Zn in soil showed that the linear regression relationship has significant positive correlation.The amount of swine manure and crop linear regression analysis showed that the linear regression between the content of Cu,Cd,Pb, Zn in wheat and rice grain and the amount of swine manure has significant positive correlation.(4)In wheatseason and riceseason,the analysis of Nemero index of heavy metals in soil showed that the single factor pollution index of Cu,Cd,Pb and Zn were less than 0.7 in the state of pollution-free.The single factor pollution index and the comprehensive pollution index of Cu,Cd,Pb in the treatment M6 is high and has been very close to the light pollution critical value of 0.7.The potential ecological risk index and the comprehensive potential ecological risk index of heavy metals in soil showed that the potential ecological risk index of Cu,Cd,Pb, Zn in soil were less than 30 in every treatment of wheat and rice seasons,which was in a state of pollution-free.The potential ecological risk index of Cd was between 16.06 and 20.78,while the risk index of Pb,Cu,Zn was from 0.51 to 3.47,which indicated that the potential ecological pollution risk of Cd in soil was greater under different fertilization treatments.The comprehensive potential ecological risk indexin every Swine manure treatments was significantly higher than that of blank treatment CK and the pure chemical fertilizer treatment CF(P< 0.05),showed that the application of swine manure to soil can making potential pollution risk.The potential ecological risk index of roots,stems and leaves of wheat and rice under different fertilization treatments were all at a slight risk level.Through the potential ecological risk index of four kinds of heavy metals,the potential ecological risk of heavy metals were dominated by Cd.Under different fertilization treatments,the single health risk coefficient of Cu,Cd,Pb,Zn in rice and wheat grains were less than 15 which showed no significant threat to human health.