Humic substances can reduce mobility and bio-accessibility of Cd in soil and therefore inhibit its uptake by rice, which is a major source of human Cd intake. Yet, the effects of aging humic substances are not fully understood. A rice pot experiment was conducted to evaluate the effects of humic acid-based amendments on the mobility of Cd in soil solution and its uptake by rice when amendments were freshly added or aged for 130 d. The results showed that the aged and the unaged amendments generally decreased Cd concentration in soil solution, but the effect declined with time. Unaged HA-K (humic-potassium) reduced Cd concentration by 88% for the first sampling, but this dropped to 46% for the last sampling, compared to that of the control. All amendments, whether aged or not, reduced the content of Cd in rice seedlings, as well as in mature plants. Aged and unaged woody peat reduced the Cd content in seedlings by 79% and in grains by 70%, respectively. Aging of amendments caused lower pH and higher Cd concentration in the soil solution for all amendments and accordingly, the Cd content in rice seedlings or each part of mature plants in the aged group was higher than that of the unaged group. The applied amendments might reduce the solubility of Cd through the alteration in soil pH, and thus inhibit the uptake of Cd by rice, but the effects diminished with aging.

腐殖质会降低土壤中Cd的迁移率和生物可及性，因此会抑制水稻对Cd的吸收，而水稻是人类Cd摄入的主要来源。然而，腐殖质老化的影响还没有被完全理解。进行了一个水稻试验，评估了腐殖酸基改良剂对新鲜或老化130 d的镉在土壤溶液中的迁移率及其对水稻吸收的影响。结果表明，老化和未老化的改良剂通常会降低土壤溶液中的Cd浓度，但效果会随着时间而降低。与对照相比，未老化的HA-K（腐殖酸钾）在第一次采样时将Cd浓度降低了88％，但在最后一次采样时降低了46％。所有的修正案，无论是否老化，都会降低水稻幼苗以及成熟植物中的镉含量。老化和未老化的木质泥炭分别使幼苗中的Cd含量降低了79％，谷物中的Cd降低了70％。修饰剂的老化导致所有修饰剂的pH值降低和土壤溶液中Cd浓度升高，因此，老年组中水稻幼苗或成熟植物各部分中的Cd含量均高于未老化组。施用的改良剂可能会通过改变土壤pH值而降低Cd的溶解度，从而抑制水稻对Cd的吸收，但随着年龄的增长，其影响减弱。老年组水稻幼苗或成熟植物各部分的镉含量均高于未龄组。施用的改良剂可能会通过改变土壤pH值而降低Cd的溶解度，从而抑制水稻对Cd的吸收，但随着年龄的增长，其影响减弱。老年组水稻幼苗或成熟植物各部分的镉含量均高于未龄组。施用的改良剂可能会通过改变土壤pH值而降低Cd的溶解度，从而抑制水稻对Cd的吸收，但随着年龄的增长，其影响减弱。