Restriction factors of Cd activity in rice root soil developed from different parent materials along the Yangtze River in Nanjing
In order to clarify the distribution rules and constraints of effective Cd and its activity(RCd)in root soil of paddy fields un-der different parent material conditions,300 root soil samples were collected from the paddy fields in the study area,and the correlation between soil RCd and the total amount,available state,pH,SOM,CEC,etc.of root soil Cd was systematically analyzed.The prediction models of RCd and its influencing factors in different blocks were constructed by multiple regression analysis.The results showed that,firstly,the average contents of total Cd,available Cd and RCd were(0.40±0.07)mg/kg,(0.13±0.05)mg/kg and(32.87±11.71)％in plain area,and(0.17±0.07)mg/kg,(0.09±0.03)mg/kg and(53.60±14.26)％in hilly area,respectively.Secondly,there was a significant positive correlation between available Cd and total Cd(p＜0.0 1),and the correlation coefficient was 0.55,but it decreased with the increase of soil pH.Thirdly,the available Cd from the same parent material was negatively correlated with pH value and SOM(p＜0.01),and the correlation coefficients were-0.29 and-0.39 in hilly area and-0.58 and-0.29 in plain area,respectively.Fourthly,RCd was extremely significant negative with the total amount of Cd in hilly areas,but weak in plain areas;it was extremely significant positive with available Cd,especially in plain areas,where the correlation coefficient was 0.80;it showed a very significant negative correlation with both SOM and CEC.Fifthly,there was almost no correlation with grain size.Sixthly,increasing soil pH,SOM and CEC can restrict the activity of soil Cd,especially when the soil pH was above or equal to 7.5,the content of SOM was above 20 g/kg and the content of CEC was above 20 cmol/kg,it can significantly inhibit the activity of heavy metal Cd.Seventhly,logarith-mic model and multiple regression analysis were used to establish quantitative relationship models of Cd activity and its influencing factors in the whole region,hilly region and plain region,respectively,which could better predict the heavy metal Cd activity in local farmland root soil.
cadmiumactivitypaddy fieldroot soilalong the Yangtze River in Nanjing
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