| Cadmium(Cd)is a primary concern and soil heavy metal pollution on the international field of the prevention and control of pollutants,under the influence of the nonferrous metal mining enterprises activities,especially in parts industrial and mining enterprises surrounding farmland soil Cd pollution problem increasingly prominent,and soil acidification,further enhanced the activity of soil Cd and migration,promote Cd accumulation in the body in crops.Soil acidification in paddy fields in southern China is one of the main factors leading to "cadmium rice".The decrease of soil pH value will enhance the availability of Cd in soil and increase the environmental risk of Cd in soil.In recent years,paddy soil acidification has been accelerated in some areas of south China due to acid deposition and extensive application of acid fertilizer.In this paper,five acid paddy fields(kunming,Chuxiong,Xinyu,Nanping and Sanming,Fujian)in Yunnan,Jiangxi and Fujian provinces were selected for field experiments.Based on three kinds of basic material(lime,lime stone powder,oyster shell powder),respectively,to adjust to two different target sites soil pH value,the comprehensive analysis of effectiveness of soil Cd,Cd content and soil physical and chemical properties,rice yield indicators,such as repair and build the soil Cd pollution evaluation system,further clarify the testbed soil Cd pollution control in the process,This study can provide technical support for the safe utilization,treatment and restoration of cadmium-contaminated cultivated land in the above experimental areas.The main results are as follows:(1)Four soil target pH values were set based on the original soil pH values in five test areas.One was kunming test site in Yunnan province,Chuxiong test site in Yunnan Province and Xinyu test site in Jiangxi Province,and the two target pH values were set as 6.5 and 7.0 respectively.The other was nanping test site and Sanming test site in Fujian province.Two soil target pH values were set as 5.5 and 6.0.Under different target pH values,the effects of application of three kinds of alkaline materials on soil Cd available content in rice harvest period were studied.The results showed that compared with the control group,application of three kinds of alkaline materials under different target pH values could reduce soil Cd available content in five test sites.Among them,soil available Cd content in Kunming,Yunnan,Chuxiong,Yunnan and Xinyu,Jiangxi test sites decreased significantly compared with the control group(P<0.05).When the soil target pH value was 6.5,soil available Cd content was reduced by 13.49% to 45.68% after the application of the three alkaline materials.When the soil target pH value was 7.0,soil available Cd content was reduced by 13.49% to 45.68% after the application of the three alkaline materials.The available Cd content of soil decreased by 20.12% ～ 50.45% after application of the three alkaline materials.For nanping test site and Sanming test site in Fujian province,when the soil target pH value was 5.5,the soil Cd available content decreased by 9.66% to 34.69% after the application of three kinds of alkaline materials;when the soil target pH value was 6.0,the soil Cd available content decreased by 27.52% to 43.86% after the application of three kinds of alkaline materials.Compared with the control group,Cd available content in soil decreased significantly(P<0.05).(2)According to different soil target pH values,three different alkaline materials(quicklime,limestone powder and oyster shell powder)were applied to adjust the soil pH value,and the soil pH value was monitored at the mature stage of rice,and compared with the set soil target pH value.The field test results showed that: In all the five test sites,the measured values of soil pH at rice maturity were closer to the set soil target pH by applying limestone powder and oyster shell powder,with a difference(decrease)of 1.54%-12.17%.The difference(decrease)between the measured soil pH value and the set soil pH value was 4.71%-14.17%,indicating that limestone powder and oyster shell powder had a more stable effect on soil acidity regulation.Studying the effect of three kinds of basic material on soil properties,the results show that compared with the control,applied three kinds of alkaline material after the test of soil organic matter,alkali-hydro nitrogen,available phosphorus and available potassium content overall showed a trend of increase,suggests three kinds of basic material in improving soil structure,improve the effect of the soil environmental quality.(3)According to different soil target pH values,the effects of three different alkaline materials(quicklime,limestone powder and oyster shell powder)on Cd content and yield of rice were investigated.The field test results showed that: In the five test sites,the application of three alkaline materials at different soil target pH values significantly reduced the content of Cd in rice(P<0.05).Compared with the control in each test area,the reduction of Cd content in rice after the application of alkaline materials was as follows: The range was 41.62%-61.04% in Kunming,Yunnan,47.14%-71.02% in Chuxiong,Yunnan,35.22%-71.83% in Xinyu,Jiangxi,31.08%-46.74% in Nanping,Fujian,and 11.11%-77.78% in Sanming,Fujian.Compared with the control,the yield of rice in the five test areas of this study was reduced in different degrees after the application of the three alkaline materials.The yield of rice in the other test sites was reduced by less than 10% except the two test sites in Yunnan.(4)A comprehensive evaluation system was established to evaluate the repair effect of three different alkaline materials.The results showed that: according to the evaluation score of repair effect,the best comprehensive repair effect was obtained by applying limestone powder at the target pH value of 7.0 in kunming,Yunnan.In the experiment site of Chuxiong,Yunnan province,it was suggested to apply oyster shell powder with the target pH value of 6.5 to achieve the best comprehensive restoration effect.In xinyu test site,Jiangxi province,it was suggested that the target pH value of 7.0 was applied with quicklime to achieve the best comprehensive restoration effect.In nanping,Fujian province,it was suggested that applying oyster shell powder with target pH value of 5.5 had the best comprehensive restoration effect.In sanming,Fujian province,it is suggested to apply limestone powder at pH 6.0 to achieve the best comprehensive restoration effect. |
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