Virginia Polytechnic Institute and State University, Department of Crop and Soil Environmental Sciences, Blacksburg, VA 24061, USA.
J Environ Qual. 2010 Feb 19;39(2):519-30. doi: 10.2134/jeq2007.0671. Print 2010 Mar-Apr.
Agronomic use of biosolids has raised concern that plant availability of biosolids-Cd will increase with time after cessation of biosolids application. It has been demonstrated that chemical extractability of Cd is persistently decreased in biosolids-amended soils. This study was conducted to determine if Cd phytoavailability in long-term biosolids-amended soils was also persistently decreased. Paired control and biosolids-amended soils were collected from three experimental sites where large cumulative rates of biosolids were applied about 20 yr ago. The pH of all soils [in 0.01 mol L(-1) Ca(NO(3))(2)] was adjusted to 6.5 +/- 0.2. Increasing rates of Cd-nitrate (from 0 to 10.0 mg Cd kg(-1) soil) enriched in (111)Cd stable isotope were added to all soils, and Romaine lettuce (Lactuca sativa L. var. longifolia Lam.) was grown in pots to bioassay phytoavailable Cd. After harvest, Cd concentrations in shoots and labile pool of Cd (Cd(L)) in soils were determined. The relationship between added salt-Cd and Cd concentrations in lettuce shoots was linear for all soils tested. Ratios of (shoot Cd):(soil Cd) slopes were highest in the control soils. Biosolids amendment decreased (shoot Cd):(soil Cd) slopes to varied extent depending on biosolids source, properties, and application rate. The decrease in slope in comparison to the control was an indication of the lower phytoavailability of Cd in biosolids-amended soils. A significant negative correlation existed between Cd uptake slopes and soil organic matter, free and amorphous Fe and Al oxides, Bray-P, and soil and plant Zn. Biosolids-Cd was highly labile (%L 80-95) except for Fulton County soil (%L = 61).
生物固体的农业利用引起了人们的关注，即生物固体施用停止后，生物固体 - Cd 的植物可利用性随着时间的推移而增加。已经证明，在添加生物固体的土壤中，Cd 的化学可提取性持续降低。本研究旨在确定长期添加生物固体的土壤中 Cd 的植物可利用性是否也持续降低。从三个实验点采集了对照和添加生物固体的土壤，这些实验点在大约 20 年前施用了大量累积的生物固体。所有土壤的 pH 值[在 0.01 mol L(-1) Ca(NO(3))(2)]均调至 6.5 +/- 0.2。向所有土壤中添加了用 (111)Cd 稳定同位素富化的 Cd-硝酸盐（从 0 到 10.0 mg Cd kg(-1)土壤），并在花盆中种植罗马生菜（Lactuca sativa L. var. longifolia Lam.）以生物测定植物可利用的 Cd。收获后，测定了地上部分的 Cd 浓度和土壤中可利用 Cd （Cd(L)）的易变池。所有测试土壤中，添加盐-Cd 与生菜地上部分 Cd 浓度之间的关系呈线性。对照土壤中的（地上部 Cd）：（土壤 Cd）斜率最高。生物固体的添加以不同程度降低了（地上部 Cd）：（土壤 Cd）斜率，具体取决于生物固体的来源、性质和施用量。与对照相比斜率的降低表明生物固体添加土壤中 Cd 的植物可利用性较低。Cd 吸收斜率与土壤有机质、自由和无定形 Fe 和 Al 氧化物、Bray-P 以及土壤和植物 Zn 之间存在显著的负相关关系。生物固体 - Cd 高度易变（%L 80-95），除了富尔顿县土壤（%L = 61）。
