College of Resources & Environment, Hunan Agricultural University, Changsha, 410128, China.
College of Resources & Environment, Hunan Agricultural University, Changsha, 410128, China.
Ecotoxicol Environ Saf. 2020 Jan 30;188:109903. doi: 10.1016/j.ecoenv.2019.109903. Epub 2019 Nov 7.
Liming has been widely used to remediate Cd-contaminated acidic soils, but the effects of consecutive liming are still unclear. Four-year liming experiments were conducted to assess the remediation of Cd-contaminated acidic paddy fields in a double rice cropping system. With four-year consecutive liming (quicklime, 2.25 t ha per season), the soil pH was increased by an average of 0.57 units (0.10-1.16 units), while the soil DTPA-Cd and available Fe and Mn were reduced by 9%, 19% and 31% (p < 0.05), respectively. The exchangeable plus water-soluble Cd fraction in soil was reduced by 17%, while the soil carbonate-, Fe/Mn oxide- and organic-bound Cd fractions were increased by 23%, 41% and 10% (p < 0.05), respectively. The Cd in rice grain was reduced by 55% for early rice and 63% for late rice (p < 0.05) and in some cases was reduced to below the Chinese allowable limit (0.2 mg kg). High annual fluctuations in rice grain Cd could be caused by variations in the field water regime and in rainfall. With consecutive liming, the soil pH, DTPA-Cd and rice grain Cd varied greatly in the first three seasons and then remained relatively less variable. Meanwhile, soil available nutrients (N, P and K) and rice grain yield were little affected by liming. Soil DTPA-Cd linearly decreased with increasing soil pH, while the reduction of Cd in rice grain logarithmically decreased with increasing soil pH and the reduction in soil DTPA-Cd in the heading stage, indicating potential implications for forecasting rice grain Cd content. Therefore, consecutive liming with quicklime can be recommended for the remediation of Cd-contaminated acidic paddy fields, though supplementary measures are still necessary.
石灰被广泛用于修复 Cd 污染的酸性土壤，但连续施用石灰的效果仍不清楚。本研究进行了为期 4 年的石灰修复 Cd 污染酸性稻田的双季稻种植试验。连续 4 年施用石灰（熟石灰，每季 2.25 t·ha），土壤 pH 值平均增加 0.57 个单位（0.10-1.16 个单位），而土壤 DTPA-Cd、有效铁和锰分别降低 9%、19%和 31%（p < 0.05）。土壤中可交换态和水溶性 Cd 含量降低了 17%，而土壤碳酸盐结合态、铁锰氧化物结合态和有机结合态 Cd 含量分别增加了 23%、41%和 10%（p < 0.05）。早稻和晚稻糙米 Cd 含量分别降低了 55%和 63%（p < 0.05），部分情况下降至中国允许限量（0.2 mg·kg）以下。早稻和晚稻糙米 Cd 含量的年际波动较大，可能是由于田间水分状况和降雨量的变化所致。连续施用石灰后，土壤 pH 值、DTPA-Cd 和糙米 Cd 在前三个季节变化较大，然后相对变化较小。同时，石灰对土壤有效养分（N、P 和 K）和水稻产量的影响较小。土壤 DTPA-Cd 与土壤 pH 值呈线性关系，而糙米 Cd 与土壤 pH 值和抽穗期土壤 DTPA-Cd 的对数关系呈线性关系，表明预测糙米 Cd 含量具有潜在意义。因此，推荐使用生石灰连续修复 Cd 污染酸性稻田，但仍需采取补充措施。
