| According to the"national soil pollution survey bulletin"jointly issued by the Ministry of environmental protection and the Ministry of land and resources in 2014,the over standard rate of heavy metal pollution in soil reached 19.4%.According to the latest analysis of soil pollution report in China's major grain producing areas,the over standard rate of heavy metal pollution has reached 21.49%,and more than 20 million tons of inedible grain are limited by heavy metal pollution every year.Therefore,in order to realize the establishment of soil quality and safety system in accordance with local conditions and promote the classification management of farmland and the division of safe production areas of crops in the"ten soil items",this study evaluated and analyzed the current situation and Countermeasures of soil pollution in the study area based on the point-to-point collection of soil,wheat and corn samples from some typical wheat and corn production areas in northern China According to the results of function model derivation,the soil cadmium(Cd)threshold of wheat and corn in northern China was explored,and different production areas were divided according to the actual situation.The methods and results of the study can provide scientific basis for the safe production of wheat and corn in the northern farmland of China,and provide ideas and reference for the formulation of soil ecological threshold standards.The main results are as follows:(1)The average values of Cd content in soil and wheat grain were 0.87 mg·kg-1and 0.14 mg·kg-1 respectively,and the exceeding standard rates were 95.1%and 47.6%according to GB 15618-2018.Except CEC and DTPA-Cd,p H,SOM and clay content of soil were significantly correlated with BCF(bioconcentration factor),and the correlation coefficients were-0.18(P<0.05),0.14(P<0.05)and-0.53(P<0.01),respectively.The regression model Lg[BCF]=-0.097p H+0.11Lg[SOM]+1.2Lg[clay content]+0.81(r=0.732,n=147)could explain 54%of the BCF variation.SSD logistic model analysis showed that Pubing 151 was the least sensitive and Xinong 979 was the most sensitive.Based on the characteristics of soil properties in northern wheat growing areas,three typical scenarios were set,when the soil was 6.5?p H<7.5(SOM=15 g·kg-1,Clay=20%),7.5?p H<8.5(SOM=30 g·kg-1,Clay=20%)and p H?8.5(SOM=20 g·kg-1,Clay=20%),the thresholds of suitable yield were 0.33,0.41 and 0.64 mg·kg-1,respectively,The thresholds of forbidden yield were1.93,2.51 and 2.61 mg·kg-1 respectively.The area with soil Cd content in a range of the suitable yield thresholds and the forbidden yield thresholds was considered as restricted for wheat-producing area's yield.(2)The results showed that the content of Cd in soil and corn kernel exceeded the standard by 99.62%and 49.61%respectively,with the average value of 3.43 and 0.36mg·kg-1,which belonged to the heavy pollution level.BCF was significantly correlated with soil p H,SOM,CEC and available Cd content(DTPA extraction)(P<0.01),and the correlation coefficients were-0.59,-0.35,0.43 and 0.78,respectively the prediction formula established by multiple linear regression method was Lg[BCF]=-0.669p H?2.881Lg[SOM]+1.79Lg[CEC]-0.603(r=0.719,n=129),and the predictability of the equation was as high as 71.9%.SSD logistic model analysis showed that Shengyu 367 was the least sensitive and Huanong 887 was the most sensitive.Based on the soil characteristics in this study and the research results of other scholars,three different soil scenarios were divided:scenario 1:6.5<p H?7.5,SOM=15 g·kg-1,CEC=15 cmol·kg-1 scenario 2:7.5<p H<8.5,SOM=20 g·kg-1,CEC=20 cmol·kg-1 scenario 3:p H?8.5,SOM=17g·kg-1,CEC=17 cmol·kg-1.According to the logistic function model of SSD method,the thresholds of suitable production area were 3.00,3.80 and 3.11 mg·kg-1 respectively the thresholds of forbidden production yield were 8.95,9.10 and 7.21 mg·kg-1respectively.The area with soil Cd content in a range of the suitable yield thresholds and the forbidden yield thresholds was considered as restricted for maize-producing area's yield. |
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