Effects And Mechanism Of Water Management And Organic Manure Coupling On Remediation Of Cadmium Contaminated Soil By Sepiolite

In China,heavy metal pollution especially cadmium contamination in agricultural soil is becoming more and more serious and has attracted wide attention.In-situ remediation technology has the advantages of rapid efficacy,good effect,simple in implement,low investment,and especially suitable for the remediation of large area of moderate and mild cadmium pollution in farmland.Sepiolite is an environmental friendly natural clay mineral.A large number of previous studies by the team showed that it has good remediation effect on heavy metal cadmium pollution in soil.However,the remediation efficiency in practical field application will be affected by agricultural management regimes,such as water management and fertilization.This study investigated the coupling effects of different water management and fertilizer on the remediation effectiveness and mechanism on cadmium pollution using sepiolite.The main results obtained are as follows:1.The experiment showed that,the application of organic fertilizer and the increase of soil water holding capacity promoted growth of rape.When the soil maintained at 60-65%of field water holding capacity,the application of chicken manure in sepiolite-amended soil increased Cd content in the edible part of rape.The main reason was that the decrease of soil pH and the increase of DOM with the application of chicken manure.However,when the soil maintained at 100%of field water holding capacity,the application of chicken manure in sepiolite-amended soil has little effect on Cd content.Because there were less drop of soil pH and less increase of soil DOM.When the soil maintained at60-65%of field water holding capacity,the application of sheep manure and wormcast in sepiolite-amended soil has little effect on Cd content in the edible part of rape.The main reason was that sheep manure and wormcast increased soil pH.When the soil mositure maintained at 100%of field water holding capacity,the application ofsheep manure and wormcast decrease Cd content in the edible part of rape.The reasons was less increase of DOM.2.The results showed that,under aerobic and intermittent flooding condition,Cd content in root was the lowest under single sepiolite treatment.The application of chicken manure in sepiolite-amended soil increased dissolved Cd in soil solution,and increased Cd content in root.The reason was that soil pH was lower than single sepiolite treatment in the reproductive growth stage of rice.Under flooded condition,Cd content in root in single sepiolite treatment was higher than control.Because,soil Eh was higher than the control in the reproductive growth stage of rice.The application of chicken manure in sepiolite-amended soil increased dissolved Cd in soil solution,and increased Cd content in root.The reason was that soil pH was lower than single sepiolite treatment in the reproductive growth stage of rice.3.In sepiolite-amended soil,Cd content of brown rice was lower than 0.2 mg·kg^-1,the maximum Cd level permitted in foods,under flooded water condition.Under flooded condition,the application of chicken manureincreased Cd content of brown rice.The reason was that the application of chicken manure increased available Cd in soil and decreased iron plaque of root.Under aerobic and intermittent irrigation condition,the application of chicken manure has little effect on Cd content of brown rice.Under flooded condition,the application of sheep manure increased Cdcontent of brown rice,and the effect decreased with the increase of content.The reason was that the application of sheep manure decreased available Cd in soil and promoting the conversion of Cd to higher active group.Under aerobic and intermittent irrigation condition,the application of sheep manure decreased Cd content of brown rice.Because sheep manure promote the conversion of Cd to lower active group.4.The two-year successive pot experiment showed that compared with single sepiolite treatment,coupling effect of the long-term flooding irrigation and the application of chicken manure and sheep manure,further reduced Cd content of brown rice while ensuring the grain yield of rice.Coupling effect of the long-term flooding irrigation and the application of chicken manure and sheep manure increased the stability of the remediation efficiency.In summary,in dry farming or paddy field,the coupling effect of water management and fertilizer on the remediation effect of sepiolite is significantly different.Selecting a scientific water management and fertilizer model can reduce the negative effect of coupling effect on the remediation effect using sepiolite.