水分管理和施用石灰对水稻镉吸收与运移的影响

通过田间试验,研究了间歇灌溉和全生育期淹水2种水分管理结合水稻分蘖期施用石灰对不同水稻生育期的土壤和水稻各组织中Cd分布与运移的影响。研究结果表明,全生育淹水和施用石灰均能升高土壤p H值,降低土壤中有效态Cd含量;施用石灰能降低土壤中酸可提取态Cd所占比例而残渣态所占比例增加。在全生育期淹水条件下施用石灰有利于改善土壤性状并提高土壤中Fe质量百分含量。与不施用石灰相比,在间歇灌溉条件下,施用石灰处理的糙米中Cd质量分数从0.86 mg/kg降低到0.56 mg/kg,而在全生育期淹水条件下,施用石灰处理的糙米中Cd质量分数从0.77 mg/kg降低到0.34 mg/kg;无论间歇灌溉还是全淹水处理条件下,施用石灰均增加了水稻总生物量。施用石灰后,在灌浆期,水稻茎叶中Cd的富集系数显著降低(P0.05);在成熟期,根和稻米中Cd的富集系数显著降低(P0.05);在全生育期淹水条件下,成熟期水稻根到茎叶转运系数和茎叶到米中转运系数均显著降低(P0.05)。水稻糙米中Cd含量与土壤中有效态Cd含量、水稻地上部Cd累积量呈显著正相关,与土壤p H值呈显著负相关。上述研究结果表明,施用石灰能够显著降低稻田土壤中Cd的生物有效性;采用全生育期淹水结合在分蘖期施用石灰是降低稻米中Cd含量有效措施且不会导致水稻减产。

Effects 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. Agricultural paddy soil contaminated by Cd has become 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 humans in some parts of southern 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 effect of Cd on human body, animal and plant, a field experiment was conducted to evaluate the effect of liming application at rice tillering stage on the distribution and migration 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 4 treatments were designed as follows: 1) Intermittent irrigation treatment, and the plot was irrigated following 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 2 times (WCK); 2) intermittent irrigation + lime (WL); 3) flooding in whole cultivation, and 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 + lime (FL). Lime (1500 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 increased significantly the soil pH values and decreased the available Cd mass fraction 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 iron (Fe) mass fraction in the soil. After liming, the Cd mass fraction of brown rice 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 reduced significantly 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 maturity stage was also decreased significantly (P<0.05). In addition, at maturity stage the translocation factor from root to shoot and that from shoot to brown rice decreased significantly under the treatment of flooding in whole growth period combined with lime application (P<0.05). The rice yield averagely increased by 10% with lime application. Correlation analysis indicated that Cd mass fraction in brown rice was significantly positively correlated with the available Cd mass fraction in soil and the Cd accumulation in aboveground part of rice, and was significantly negatively correlated with soil pH value. In all, 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 uptake of Cd in rice in contaminated paddy soil without yield loss, especially the flooding treatment combined with lime application.