Study On The Correlation Between Available Cadmium In Soil And Cadmium Content In Rice Under Different PH Paddy Fields

Rice is the main food product in China,and ensuring rice safety is an important issue in current food security.With the rapid development of agriculture,the problem of heavy metal pollution in rice fields in China has become increasingly prominent,it is also manifested by the combined pollution of various heavy metal elements,mainly cadmium（Cd）pollution.Hunan province is the hometown of non-ferrous metals.In recent years,the“cadmium-millimeter”incident has caused serious losses to agricultural production in Hunan province and poses a threat to the health of the people.The total Cd content of soil only represents the"storage"of soil total Cd,and does not indicate the chemical activity,bioavailability and impact on human and ecological environment of Cd.Therefore,researchers believe that the effective Cd content of soil should be used as a criterion for evaluating the biological and environmental effects of Cd.Therefore,it is of great guiding significance to select the appropriate type of extractant to obtain the effective Cd content to characterize the bioavailability of soil Cd.The predecessors mainly screened the acid soil extracting agent in Hunan,however,less research is conducted on the soil with different pH and different Cd pollution levels.Therefore,this paper collects typical paddy soils with different pH in Hunan Province,and explores the effects of different concentrations of exogenous Cd(CK（T1）,0.45（T2）,0.60（T3）,0.90（T4）,1.20（T5）,1.50（T6）,2.00（T7）mg kg^-1)on the growth and development of double-cropping rice and Cd content of rice by pot experiment,compare the difference of extraction effects of 10 different extractants,and analyze the correlation between Cd content in mature rice and obtain the corresponding optimal extractant.The research results are as follows:（1）During the early rice growth season（Wufengyou 286）and the late rice growth season（Hyou518）,the yield of paddy rice grown in three paddy soils was neutral soil>acid soil>alkaline soil,and the difference was not significant（P>0.05）.The average rice yield of early and late rice in neutral soil increased by 5.8%and 10.9%compared with acid soil and alkaline soil,respectively.There is no significant difference in yield between the two seasons of Cd concentration treatment（P>0.05）.（2）During early rice growth season,the Cd enrichment coefficients of rice in acidic soil,neutral soil and alkaline soil ranged from 20.0%to 40.0%,7.3%to 15.4%and 9.6 to 18.7%respectively;In late rice growth season,the Cd enrichment coefficients of rice in acidic soil,neutral soil and alkaline soil ranged from 14.9%to28.8%,10.9%to 13.9%and 10.8%to 17.2%respectively.The Cd enrichment coefficient of rice treated with T1^T6 in early rice growth season increased with the increase of exogenous concentration.T7 treatment decreased slightly compared with T6 treatment;there was no significant difference in Cd enrichment coefficient between different soil treatments in late rice growth season（P>0.05）.The Cd enrichment coefficient of late rice in the late rice growth season increased significantly by 12.7.0%compared with the early rice growth season（P<0.01）.（3）The accumulation of Cd in acid soil and alkaline soil in early and late rice was increased by 48.0%and 16.0%compared with neutral soil.The Cd content in all parts of rice showed roots>stems and leaves>rice.during the early and late rice growth season,the Cd content of T1^T7 treated rice increased with the increase of exogenous Cd concentration.（4）Soil pH value was negatively correlated with Cd enrichment coefficient of early and late rice(-0.450^**,-0.285^*),and soil organic matter（SOM）was negatively correlated with Cd enrichment coefficient of late rice(-0.697^**,-0.521^*).The correlation between soil cation exchange capacity（CEC）and rice Cd enrichment coefficient was not significant（P>0.05）.（5）The selected ten extractants generally have a higher extraction rate of effective Cd in acid soil.The weak acid solution（0.1M HCl,0.43M HNO₃）has strong extraction ability for acidic and neutral soil,and weak extraction ability for alkaline soil;Chelating agents（M3,EDTA,DTPA）and neutral salts（1M MgCl₂）have moderate extraction ability for acidic,neutral and alkaline soils;Neutral salts（0.1M CaCl₂,0.05M CaCl₂,0.01M CaCl₂,1M NH₄OAc）have lower extraction capacity.（6）During early rice growth season,within the concentration range of<0.6 mg·kg^-1 Cd,the correlation between available Cd content in acid soil and neutral soil extracted by 0.1 M HCl and rice Cd content was higher(0.895^**and 0.903^**).The correlation between soil available Cd content in alkaline soil extracted by DTPA and rice Cd content was higher(0.879^**).Within the concentration range of 0.6².0 mg·kg^-1 Cd,the correlation between the available Cd content of DTPA and the Cd content of rice was higher.In late rice growth season,the available Cd content of soil in acidic,neutral and alkaline soils extracted by 0.1 M HCl,1 M NH₄OAc and M3 was highly correlated with the Cd content of rice(0.934^**,0.765^**,0.854^**).（7）In the two seasons,0.1 M HCl is recommended as an extractant for effective Cd in acid soil and neutral soil in the range of<0.6 mg·kg^-1 Cd.M3 is recommended as an extractant for effective Cd in alkaline soil;Within the range of 0.6².0 mg·kg^-1Cd concentration,EDTA is recommended as an extractant for effective Cd in acid soil.DTPA is recommended as an extractant for effective Cd in neutral and alkaline soil.