石灰与磷肥对籽粒苋吸收镉的影响

Effects of lime and phosphate fertilizer application on the cadmium uptake by grain amaranth

籽粒苋(Amaranthus hypochondriacus L.)是我国广泛栽种的牧草,但具有富集重金属Cd的特性,探讨减少其吸收镉的方法技术,可以降低人畜受害风险。研究利用温室盆栽方法,比较了施用磷肥和石灰对降低籽粒苋Cd吸收量的影响。于含镉5mg·kg-1的污染菜园土中,以粉末形式加入3g·kg-1Ca(OH)2,或以液态形式加入磷肥(0.326g·kg-1Ca(H2PO4)2)至P浓度80mg·kg-1,该施用量为农业应用常规水平。播种籽粒苋,于60d后收获,测定相关参数。结果表明,施用石灰使土壤pH上升1.7单位,土壤有效Cd下降至极低水平,从而大幅降低籽粒苋Cd吸收量,较对照下降约56%,但施石灰也使土壤供磷量下降,使籽粒苋的生物量也减少了约一半。施用石灰后,土壤的Ca与K供应量以及籽粒苋体内Ca与K含量均明显增加,Ca、K与Cd形成的竞争吸收也是施用石灰后籽粒苋Cd含量下降的一个原因。本地菜园土含有较高的有效磷,以常规农业磷肥施用量施用磷肥对籽粒苋吸收Cd没有明显影响,对生物量也没有明显影响,但适当提高施用量预期会有一定的效果。因而,对广州地区菜园土,使用合理的石灰施用量,可有效降低籽粒苋Cd吸收量。

Grain amaranth （Amaranth hypochondriacus L.） has been widely cultivated as fodder in China. Unfortunately, it often accumulates high level of Cd from contaminated soil, and increases the risk of human health. A greenhouse experiment was conducted to evaluate the effects of lime and phosphate application on the Cd uptake by grain amaranth. Soil was sampled from typical vegetable land in Guangzhou, China, and artificially contaminated to 5 mg·kg-1. Four replicates were set for all three treatments： （1） control, （2） phosphate： applied with Ca（H2PO4）2 solution to 80 mg of P kg-1 and （3） lime： applied with lime powder to 3 g of Ca（OH）2 kg-1. The application rates employed are of ordinary agricultural practice in this region. Grain amaranth was sowed to pots, harvested at day 60 and determined for different parameters. Lime decreased Cd content in amaranth by 56%, which might result from an increase of soil pH by 1.7 units, and then a decrease of Cd availability in soil to trace level. However, lime application reduced biomass of grain amaranth by 50% in comparison to the control. Decreased P supply in soil might account for biomass reduction in lime treatment. Lime increased Ca and K supply in soil and Ca and K content in grain amaranth, which might partly be responsible for reduction of Cd uptake as a result of cation competition. Phosphate application had no obvious effects on both the biomass and the Cd content of grain amaranth. The results suggested that a proper application rate of lime might be feasible in reducing Cd uptake of grain amaranth.