Aims Many soil scientists think that soil phosphate exists as discrete compounds of iron, aluminium and calcium and, accordingly, use chemical fractionation schemes to identify these compounds. Methods We reacted a sample of goethite and a sample of aluminium oxide with a phosphate solution under conditions chosen to facilitate penetration of phosphate. Thus the sample of goethite had neither calcium nor aluminium present and similarly the sample of aluminium oxide had neither iron nor calcium. We included a sample of hydroxyapatite which had neither iron nor aluminium present. We subjected the samples to two fractionation procedures; the original Chang and Jackson ( 1957 ) method and a variant of it. Results For the phosphated goethite and aluminium oxide, energy dispersive X-ray spectra did not detect any discrete aluminium or iron phosphates; dissolution studies were consistent with penetration of phosphate. Both fractionation procedures detected discrete compounds even though none were present. They also detected iron, aluminium and calcium phosphates for samples for which they were not present. We also critically discuss other evidence for the existence of discrete iron, aluminium and calcium phosphates in soils. Conclusions Fractionation procedures designed to measure chemically specified phosphate fractions in soil are fallacious and should be abandoned.

中文翻译：

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土壤磷酸盐分馏谬误

目标 许多土壤科学家认为土壤磷酸盐以铁、铝和钙的离散化合物形式存在，因此，使用化学分馏方案来识别这些化合物。方法 我们将针铁矿样品和氧化铝样品与磷酸盐溶液在选择的促进磷酸盐渗透的条件下反应。因此针铁矿样品既没有钙也没有铝存在，同样氧化铝样品既没有铁也没有钙。我们包括了一个不含铁和铝的羟基磷灰石样品。我们对样品进行了两个分馏程序；最初的 Chang 和 Jackson (1957) 方法及其变体。结果 对于磷化针铁矿和氧化铝，能量色散 X 射线光谱未检测到任何离散的铝或铁磷酸盐；溶解研究与磷酸盐的渗透一致。两种分馏程序都检测到离散化合物，即使不存在。他们还检测到铁、铝和钙的磷酸钙，而这些样品中不存在磷酸铁、铝和钙。我们还批判性地讨论了土壤中存在离散磷酸铁、磷酸铝和磷酸钙的其他证据。结论 旨在测量土壤中特定化学磷酸盐分数的分馏程序是错误的，应该放弃。土壤中的磷酸铝和磷酸钙。结论 旨在测量土壤中特定化学磷酸盐分数的分馏程序是错误的，应该放弃。土壤中的磷酸铝和磷酸钙。结论 旨在测量土壤中特定化学磷酸盐分数的分馏程序是错误的，应该放弃。