| Soil heavy metal pollution is an important environmental problem in China.Excessive cadmium is the most serious problem.Cadmium is a highly toxic heavy metal.The cadmium in soil is mainly migrated and transformed in the form of Cd~2+and its compounds.Its activity is mainly affected by environmental p H,microorganisms and other heavy metal elements.Excessive accumulation of cadmium in plants can inhibit its growth.Cadmium accumulates mainly in organs in animals,causing malformations and canceration of organs such as kidneys,liver and lungs.After entering the human body,calcium can be replaced from the bone,causing the bones diseases.China’s farmland soil cadmium pollution is very serious.In this paper,six commercial soil conditioners(lime,Tian Shi Fu,Yue Tian,Feng Shou Yan,Jin Kui Zi and Jin Wu Zong)were selected from the market of cadmium-polluted farmland in Huizhou City,Guangdong Province.The effects of cadmium pollution on soil were compared by two rice planting.Sothat we can find out the best option for the local environmental characteristics and the current situation of farmers.The conclusions are as follows:(1)Soil conditioners containing basic ingredients can significantly increase the p H of cultivated land and surrounding soil.In addition,the effect of soil conditioner with multiple alkaline components on cadmium solidification is better than that with single alkaline component.The addition of Phosphorus and Silicon can effectively improve the curing performance of the conditioner.The basic component of Tian Shifu group is Ca-Mg-P combination,while that of Yue Tian group is Ca-Mg-Si combination.The curing effect of both groups is better than that of lime group with pure Ca O.It is suggested that alkaline soil conditioners should be used.(2)Soil conditioner with high silicon content hinders the adsorption of cadmium by rice more significantly.The silicon content in Yue Tian group,Fengshouyan group and Jinkuizi group was 12%,4%and 5%respectively.The results showed that the content of Cd in rice leaves with silicon was significantly lower than that without silicon,and that in Yue Tian group with high silicon content,the content of Cd in rice was significantly lower than that in Fengshouyan group and Jinkuizi group with low silicon content.The cadmium content in rice leaves and rice is determined by two aspects:the curing ability of the conditioner and the ability of blocking the adsorption.Silicon can form alkaline combination with Ca and Mg,and strengthen the solidification of Cd by changing the soil shape.Silicon itself has the ability to forcibly hinder the adsorption of Cd by rice.It is the core element of controlling Cd pollution.Therefore,it is suggested to use a conditioner with high silicon content.(3)The results showed that cadmium was abundantly concentrated in stems and leaves,and the cadmium content in rice leaves accounted for 37%～65%of the total cadmium content,and the proportion increased with the pollution degree.In view of the strong cadmium accumulation ability of rice leaves,it is not recommended that farmers use straw returning technology in paddy fields.Returning straw to the field is equivalent to filling most of the cadmium elements back into the soil,but the existing conditions can not confirm whether this part of cadmium elements cause secondary absorption,thus polluting the next planting.(4)Microbial fertilizer conditioner are powerful and environmentally friendly,and do not cause secondary pollution,but the effect fluctuates greatly.Its core component is effective living bacteria,and microorganisms are susceptible to environmental impact,bacterial activity is difficult to guarantee,temperature,p H,humidity and other changes may cause a devastating impact on microorganisms.This requires that agricultural managers have a higher level of knowledge to control.It is not recommended for general farmers to use biological agents.(5)After the application of six soil conditioners,the main nutrients(Nitrogen、Phosphorus and Potassium)of paddy fields were not significantly affected,nor did they have significant effects on rice yield.Two seasons of rice planting were carried out.According to the conventional planting methods of local farmers,seedlings were raised independently and fertilized three times after transplanting.The whole growth period was142 days.The average output of each plot was 1004.1 kg/hm~2in the last quarter and 1029.2kg/hm~2in the next quarter.It corresponds to the local productivity level.To sum up,the six soil conditioners involved in the experiment,Yue Tian soil conditioner,have the best application value.Its core component is silicon,which has a strong effect in solidifying cadmium in soil and preventing rice from adsorbing cadmium.The Jinwuzong conditioner is also quite effective.Farmers are recommended to use them with strong technical support.According to the results of the whole experiment,it is necessary not only to select suitable soil conditioner,but also to protect the relevant administrative regulations and agricultural management. |
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