| In recent years,Cd pollution in farmland has been widely concerned by environmental researchers at home and abroad.The excessive Cd of rice has seriously threatened human health.Therefore,the treatment of brown rice Cd is urgent.Zn and Cd are akin elements and have similar chemical properties.They are the main competitors in the soil Cd adsorption site and the Cd absorption and transport process in plants.Studies at home and abroad have found that Zn-Cd interactions vary greatly depend on rice varieties,soil Cd content,Zn content and application methods.Whether the relationship between Zn-Cd is synergistic,antagonistic,additive or irrelevant is still inconclusive.In this study,pot experiments and field trials were carried out by the soil application,foliar application,mixed application(soil application+spraying)of Zn fertilizer and compound conditioning agent,soils with different Cd pollution levels,different rice varieties,different application methods and under different cultivation models,the contents of exchangeable Cd and Zn in soil,the rice growth stages,Cd and Zn contents in various parts of rice were analyzed,and the migration and transport of Cd in soil-rice system and the relationship between Zn-Cd were investigated.The main results from this research are given as follows:(1)The results of Zn application in potted soil of rice showed that Zn fertilizer in soil significantly increased the number of iron plaque on the root surface of two kinds of rice in two Cd-polluted soils with Cd contents of 0.50 mg·kg-1 and 1.50 mg·kg-1.These increases were 14.7%～85.9%and 5.8%～61.2%for Xiangwanxian 12 and weiyou 46,respectively,which improved the resistance and control ability of rice to Cd.Soil application of Zn fertilizer significantly reduced the Cd content in brown rice of Xiangwanxian 12 and Weiyou 46 by 13.4%to 78.4%and 14.7%to 79.8%,respectively.In soil,soil application of Zn fertilizer could reduce Cd contents of brown rice in Xiangwanxian 12,but the application of Zn content higher than 40 mg·kg-1 would increase Cd contents of Weiyou 46 brown rice.All Cd contents in brown rice were lower than 0.02 mg·kg-1 and met to the National Standard for Brown Rice.(2)The spraying of Zn fertilizer could reduce the Cd contents of brown rice under the two cultivation modes,and the reduction rate increased with the increase of Zn fertilizer concentration.Compared with the control,3.4%～49.1%and 52.8%～67.3%of the Cd contents of brown rice were obtained in the pot and field experiements respectively.In the pot experiment,the content of Cd in brown rice was lower than 0.2 mg·kg-1 in each treatment,and the application of Zn fertilizer with a concentration of 0.4 g·L-1 could reduce the content of Cd in brown rice to the safety standard.When Zn fertilizer was mixed with LS(an amendment for soil),the application of Zn fertilizer could effectively reduce the content of Cd in brown rice under the conditions of pot experiment.On the basis of soil application of 40 mg·kg-1 of Zn fertilizer,spraying 0.1,0.2,0.4 g·L-1 of Zn fertilizer decreased by 35.8%,35.2%and 11.6%,respectively.High concentration of Zn might promote the absorption of Cd in rice,and there was a synergistic effect between Cd and Zn.Under the condition of field experiment,each treatment could reduce the content of Cd in brown rice,but only when Zn fertilizer and LS were mixed,the content of Cd in brown rice was lower than the national standard of pollutant limit.(3)Soil application,foliar application and mixed application of Zn fertilizer all increased rice biomass,but when the concentration of exogenous Zn was higher,rice growth was inhibited and biomass decreased.Under the three Zn application modes,the Zn content in all parts of rice(brown rice,chaff,stem,leaf and root)showed a trend of increasing with the increase of exogenous Zn concentration.Rice Zn content was mainly concentrated in the chaff and stems and leaves for foliar application.The application of exogenous Zn had no significant effect on the exchangeable Cd content in rice soil.The application of LS significantly reduced the exchangeable Cd content in rice soil.Under the three Zn application modes,the Cd/Zn ratio of all parts of rice was significantly lower than that of the control,which reduced the healthy risk of excessive Cd in brown rice.(4)Under the soil application of Zn fertilizer,there were significant negative correlations between Cd and Zn contents in brown rice in two kinds of Cd pollution soils(p<0.01).Zn inhibited the absorption and accumulation of Cd in brown rice,and Zn-Cd showed an antagonistic relationship.Foliar application of Zn fertilizer under pot experiment conditions,there was a significant correlation between Cd and Zn contents in various parts of rice,but there was a significant negative linear correlation in field experiments.Cd was mainly enriched in the stem,leaf and rice husk of rice,and inhibited the transport of Cd to brown rice.(5)In the field experiment,the content of Cd in various parts of rice was much higher than that in the pot experiment.The study suggested that in the high Cd contaminated soil,we could reduce the Cd content of brown rice by spraying high concentration Zn fertilizer,mixed application of Zn fertilizer,and compound LS to achieve safe rice production. |
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