调理剂配合紫云英还田降低水稻土镉的生物有效性

  【目的】  研究紫云英(Astragalus sinicus L.)还田及配施石灰或生物炭等不同土壤调理剂，对镉(Cd)污染水稻土中Cd有效性及水稻吸收转运Cd的影响，以期为我国南方Cd污染稻田的修复和水稻的安全生产提供理论依据和技术支撑。  【方法】  盆栽试验在湖南省土壤肥料研究所科研实验基地进行，供试土壤为重度污染的水稻土 (总镉 1.27 mg/kg、有效镉0.15 mg/kg)。以水稻收获后冬闲为对照(CT)，设冬季种植并翻压等量紫云英3个处理:紫云英单独还田(GM)、紫云英还田+石灰(GL)、紫云英还田+生物炭(GB)。在水稻分蘖期和成熟期，测定土壤主要理化性质和有效Cd含量，测定水稻各器官吸收和富集Cd量，并于成熟期测定水稻产量。  【结果】  1) GM处理提高了水稻分蘖期土壤有效Cd含量和水稻根部Cd富集系数，但GM处理降低了分蘖期水稻茎叶Cd含量，对稻米中Cd含量没有显著影响；GM处理对水稻成熟期土壤pH无显著影响，但提高土壤微生物量碳(MBC)的效果最好(P<0.05)。2) GL处理和GB处理均显著提高了土壤pH，降低了土壤Cd活化率和有效Cd含量，两处理分别平均降低了分蘖期水稻根部Cd累积量55.4%和57.8%。与紫云英单独还田(GM)相比，紫云英配施石灰还田(GL)减少了稻米中Cd的累积量，而紫云英配施生物炭还田(GB)提高了成熟期水稻根部Cd富集系数和茎叶–籽粒的Cd转运系数，导致水稻籽粒中Cd含量(0.08 mg/kg)显著高于对照(低于国家稻米Cd含量标准)。3)冗余分析(RDA)和随机森林模型预测结果显示，土壤pH、可溶性有机碳(DOC)和土壤有效磷(AP)是决定土壤Cd生物有效性的最重要的环境因子。  【结论】  紫云英还田提高了水稻产量，配施石灰或生物炭还田可通过提高土壤pH而有效降低土壤有效Cd含量。紫云英配施石灰可减少稻米中的Cd含量，而紫云英配施高量生物炭则会增加稻米Cd污染的风险。

Soil conditioners with Chinese milk vetch reduce Cd bioavailability in paddy soil

  【Objectives】  This study evaluated the effects of combining application of milk vetch (Astragalus sinicus L.) and different soil conditioners (lime or biochar) on the bioavailability of cadmium (Cd) in paddy soil and its accumulation and translocation in rice, in order to provide a theoretical and technical support for the restoration of Cd contaminated paddy fields and the cleaner production of rice in China.  【Methods】  A pot experiment was carried out in Hunan Province, using moderate Cd contaminated paddy soil (Total Cd 1.27 mg/kg, available Cd 0.15 mg/kg). The four treatments included the control with single cropping rice (CT), and three treatments of milk vetch incorporation as milk vetch alone (GM), milk vetch + lime (GL), and milk vetch + biochar (GB) in a milk vetch-rice rotation. At the tillering and matured stages of rice, soil properties and available Cd content were measured, and the absorption and accumulation of Cd in various parts of rice as well as rice yield were analyzed.   【Results】  1) GM increased the available Cd content in soil and Cd enrichment coefficient in rice roots at tillering stage, but GM decreased the Cd content in stems and leaves at tillering stage, and had no significant effect on Cd content in grain. 2) Both GL and GB significantly increased soil pH, decreased soil Cd activation rate and available Cd content, and the two treatments reduced the average Cd accumulation in rice roots by 55.4% and 57.8% at tillering stage, respectively. Compared with GM, GL reduced the accumulation of Cd in grain, while GB increased the Cd enrichment coefficient in the roots of rice at maturity and Cd transport coefficient from stem and leaf to grain, resulting in a significantly higher Cd content in grains (0.08 mg/kg), but lower than the national standard permitted for rice Cd content. 3) Redundancy analysis (RDA) and random forest model predictions showed that soil pH, soil soluble organic carbon (DOC), and available phosphorus (AP) were the most important factors in determining the bioavailability of Cd at 0–15 cm paddy soil depth.   【Conclusions】  The application of milk vetch combined with lime or biochar effectively reduces soil available cadmium by increasing soil pH thus improving rice yield. Milk vetch combined with lime reduces the content of Cd in rice, while the addition of milk vetch and a large amount of biochar increases the risk of Cd contamination in rice.