Effect of lime and water management on uptake and translocation of cadmium in rice
【Abstract】Cadmium (Cd) is a highly toxic element, and can be readily accumulated in crops and thus harm human health by food chain. The agricultural paddy soil contaminated by Cd has become a very obvious environmental problem in South China. Rice (Oryza sativa L.) is a kind of important crop and main daily diet and has been considered to be a major source of Cd intake by human in some parts of South China. The accumulation of Cd in rice in Cd-contaminated paddy field easily exceeds 0.2 mg/kg, which is the limit according to the National Standard of Pollutant in Food of China (GB 2762-2012). In order to reduce the effects of Cd on human body, animal and plant, a field experiment was conducted to evaluate the effects of lime application at rice tillering stage on the distribution and translocation characteristics of Cd in organs of rice at the different growth stages under the treatment of intermittent irrigation and flooding in whole growth period. The four treatments were designed as follows. 1) Intermittent irrigation treatment. The plot was irrigated with the local conventional irrigation method to maintain being flooded with 3–5 cm water above the soil surface until the late tillering stage and then was drained, followed by intermittent irrigation two times (WCK). 2) Intermittent irrigation + lime (WL). 3) Flooding in whole cultivation period. The plot was flooded during the whole period of crop growth, in which water was kept at a height of 3–5 cm above the soil surface (FCK). 4) Flooding in whole cultivation period + lime (FL). Lime (1 500 kg/hm2) was applied to the paddy soil after the samples were collected at tillering stage. The samples were collected at stages of tillering, filling and maturity, respectively. The results showed that the intermittent and continuous flooding treatment combined with lime application at rice tillering stage significantly increased the soil pH value and decreased the mass fraction of available Cd in the soil. Application of lime caused the transforming of acid-soluble Cd into oxidizable, reducible and residual states. Moreover, application of lime in the treatment of flooding in whole growth period could increase the iron (Fe) mass fraction in the soil. After liming, the Cd mass fraction of brown rice was significantly reduced from 0.86 to 0.56 mg/kg under intermittent irrigation treatment and from 0.77 to 0.34 mg/kg under the treatment of flooding in whole growth period. Meanwhile, lime application significantly reduced the bioconcentration factor of Cd in shoot at filling stage (P < 0.05), while the bioconcentration factor of Cd in root and brown rice at mature stage was also decreased significantly (P < 0.05). In addition, at mature stage, the translocation factor from root to shoot and that from shoot to brown rice was decreased significantly under the treatment of flooding in whole growth period combined with lime application (P < 0.05). The rice yield was increased by 10% with lime application on average. The correlation analysis indicated that the Cd mass fraction in brown rice was significantly positively correlated with the mass fraction of available Cd in soil and the Cd accumulation in aboveground part of rice, and was significantly negatively correlated with the soil pH value. In summery, the results indicated that the intermittent irrigation and flooding in whole growth period combined with lime application at tillering stage were effective ways to reduce the uptake of Cd in rice in contaminated paddy soil without yield loss, especially the flooding treatment combined with lime application.
【Keywords】 water management; lime; heavy metal; rice; cadmium; bioconcentration factor; translocation factor;
(Translated by CHEN T)
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