Effects Of Different Managements Of Irrigation Water On Migration And Accumulation Of Cd In Rice Plants

In this work,the effects of different managements of irrigation water on migration and accumulation of Cd in rice plants were investigated in two pollution soils with 5 mg-kg-1(No.A)and 10 mg-kg-1(No.B)of Cd.A pot experiment was conducted to study the effects of four modes of different managements of irrigation water on soil Eh values,bioavailability of soil Cd,Cd contents in all rice tissues,translocation factors and bioconcentration factors of Cd in rice at different stages(tillering stage,filling stage and mature stage).These four modes of different managements of irrigation water were moistening throughout the entire period of rice growth(M),moistening before filling stage and flooding after filling stage(M-F),flooding before filling stage and moistening after filling stage(F-M),flooding throughout the entire period of rice growth(F).Further systematic studies were carried out to investigate the relations between the soil Eh values and the contents of Cd in all rice tissues.Meanwhile,the influence of soil water content on the Cd absorbed by rice plants was investigated.The main results are as follows:(1)M treatment increased soil Eh values,and the soil was in oxidation state.F treatment decreased soil Eh values,and the soil was in reduction state.M-F treatment decreased soil Eh values rapidly,while F-M treatment increased soil Eh values rapidly.The exchangeable contents of Cd and TCLP-Cd contents in soil decreased gradually with extending periods of rice growth.(2)Compared with M,the other three modes(F-M,M-F,F)significantly reduced Cd contents in all rice tissues,including roots,stems,husks and brown rice.For the pollution degree of A,Cd contents in brown rice due to the treatments of M-F and F were 0.19 mg-kg-1 and 0.10 mg-kg-1,respectively.For the pollution degree of B,Cd contents in brown rice reached 0.07 mg·kg-1 for F treatment.On this basis,Cd contents were lower than the limits of 0.2 mg·kg-1 of the national food safety standards.(3)The most significant influence of different managements of irrigation water on translocation factors(TF)of Cd was from roots to stems,which was in the order:TFM>TFF-M>TFM-F>TFF.At the same mode,the translocation factor of Cd from stems to husks reached the maximum,the translocation factor of Cd from husks to brown rice was the next,and the translocation factor of Cd from roots to stems was the last.(4)For the four modes,the bioconcentration factors of Cd in all rice tissues,including roots,husks and brown rice,were in the order:BCFM>BCFF-M>BCFM-F>BCFF.(5)For the two pollution levels,there was significantly correlation between soil Eh values and Cd contents in all rice tissues.The soil Eh values of 50?75 mV might be the threshold range,which causes great accumulation of Cd in rice rapidly.Simultaneously,maintaining soil Eh values less than 50 mV could decrease greatly absorption and accumulation of Cd in rice plants.(6)Soil Eh values and available Cd contents decreased gradually with increase in soil water content.When soil water content was higher than 80%,Cd contents in brown rice decreased significantly in medium-level Cd soil(1.5 mg·kg-1).