水分管理模式与土壤Eh值对水稻Cd迁移与累积的影响

通过水稻盆栽试验,研究了4种水分管理模式水稻全生育期湿润灌溉(M)、灌浆期湿润和灌浆期后淹水灌溉(M-F)、灌浆期淹水和灌浆后湿润灌溉(F-M)、全生育期淹水灌溉(F)]对土壤Eh值、Cd生物有效性及对水稻Cd迁移与累积的影响.结果表明土壤Eh值从负值变为正值时,土壤交换态Cd含量先升高后降低.与M处理相比,F-M、M-F、F处理显著降低水稻根、茎叶、谷壳、糙米Cd含量,其中M-F和F处理水稻糙米Cd含量分别为0.19 mg·kg~(-1)和0.10 mg·kg~(-1),均低于国家食品污染物限量0.2 mg·kg~(-1)的标准(GB 2762-2012).与M处理相比,F-M、M-F、F处理显著降低水稻地上部Cd累积量和水稻中Cd的转运系数.水稻地上部分Cd累积量、水稻中Cd的转运系数、水稻糙米Cd含量与土壤Eh值均存在正指数关系.4种水分管理模式中,M-F处理的水稻产量最高.虽然威优46被认为是Cd高累积水稻品种,但是在5 mg·kg~(-1)的Cd污染土壤中进行适当的水分管理,威优46糙米Cd含量也能够达到国家标准.因此,为了保证水稻的食品安全和水稻产量,建议采用M-F处理作为水分管理模式,且灌浆期后的土壤Eh值保持在-160~-130 m V范围.

Effects of Different Water Managements and Soil Eh on Migration and Accumulation of Cd in Rice

A pot experiment was conducted to study the effects of four modes of water managements on soil Eh values,bioavailability of soil Cd,migration and accumulation of Cd in rice.These four modes of water managements 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),and flooding throughout the entire period of rice growth (F).The results indicated that the exchangeable contents of Cd increased firstly and then declined with the soil Eh values changing from negative to positive.Compared with M,the other three modes (M-F,F-M,and F) significantly reduced the contents of Cd in all rice tissues,including roots,stems,husks and brown rice.Meanwhile,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.These Cd contents were lower than the limits of 0.2 mg·kg^-1 in national food safety standard (GB 2762-2012).Compared with M,the other three modes significantly decreased Cd accumulation amounts in the aboveground parts of rice and also decreased Cd translocation factors in rice.There were significant positive exponential relations between soil Eh values and Cd accumulation amounts in the aboveground parts of rice,Cd translocation factors in rice,or Cd contents in brown rice.The rice biomass due to M-F treatment reached the maximum among the four modes.It was worthy to be mentioned that although Weiyou 46 was considered a variety rice with high Cd accumulation,Cd content in rice brown of Weiyou 46 could be lower than 0.2 mg·kg^-1 in the 5 mg·kg^-1 of Cd contaminated soil through proper water managements.In summary,M-F treatment ensured high rice yield with low Cd contents in brown rice and could be recommended as the irrigation mode in rice production.Simultaneously,maintaining soil Eh value between -160--130 mV was also important after the filling stage.