Department of Soil Quality, Wageningen University, P.O. Box 47, 6700 AA, Wageningen, The Netherlands.
Environ Sci Technol. 2011 Jan 1;45(1):262-7. doi: 10.1021/es1016119. Epub 2010 Dec 8.
A 0.01 M CaCl(2) extraction is often used to asses the bioavailability of plant nutrients in soils. However, almost no correlation was found between selenium (Se) in the soil extraction and Se content in grass. The recently developed anion Donnan membrane technique was used to analyze chemical speciation of Se in the 0.01 M CaCl(2) extractions of grassland soils and fractionation of DOC (dissolved organic carbon). The results show that most of Se (67-86%) in the extractions (15 samples) are colloidal-sized Se. Only 13-34% of extractable Se are selenate, selenite and small organic Se (<1 nm). Colloidal Se is, most likely, Se bound to or incorporated in colloidal-sized organic matter. The dominant form of small Se compounds (selenate, selenite/small organic compounds) depends on soil. A total of 47-85% of DOC is colloidal-sized and 15-53% are small organic molecules (<1 nm). In combination with soluble S (sulfur) and/or P (phosphor), concentration of small DOC can explain most of the variability of Se content in grass. The results indicate that mineralization of organic Se is the most important factor that controls Se availability in soils. Competition with sulfate and phosphate needs to be taken into account. Further research is needed to verify if concentration of small DOC is a good indicator of mineralization of soil organic matter.
0.01M CaCl2 提取法常用于评估土壤中植物养分的生物有效性。然而，土壤提取液中的硒（Se）与草中的硒含量之间几乎没有相关性。最近开发的阴离子 Donnan 膜技术被用于分析草地土壤 0.01M CaCl2 提取液中硒的化学形态和 DOC（溶解有机碳）的分馏。结果表明，提取液中（15 个样本）的大部分硒（67-86%）以胶体大小的硒存在。可提取硒中只有 13-34%是硒酸盐、亚硒酸盐和小分子有机硒（<1nm）。胶体硒很可能是与胶体大小的有机物结合或掺入其中的硒。小分子硒化合物（硒酸盐、亚硒酸盐/小分子化合物）的主要形式取决于土壤。总共有 47-85%的 DOC 为胶体大小，15-53%为小分子有机物（<1nm）。结合可溶性硫（S）和/或磷（P），小分子 DOC 的浓度可以解释草中硒含量的大部分变异性。结果表明，有机硒的矿化是控制土壤中硒有效性的最重要因素。需要考虑与硫酸盐和磷酸盐的竞争。需要进一步研究以验证小分子 DOC 的浓度是否是土壤有机质矿化的良好指标。
