Is selective identification of poorly crystalline aluminum hydroxides in soils of temperate latitude possible?

Abstract Aluminum (Al) is one of the most abundant elements in soils. As poorly crystalline Al hydroxides are reactive toward soil organic matter (SOM), they are thought to be involved in SOM stabilization. This is also inferred from correlations between soil organic carbon contents and those of Al extracted by acid oxalate in darkness (AOD), although it is known that several species release Al by this extraction. We tested the completeness of dissolution by AOD of synthesized poorly crystalline Al hydroxides and models of Al in organic association, which included dissolved organic matter flocculated by Al ions and Al adsorbed on peat. While Al was almost completely extracted from the organic models, all hydroxides were completely dissolved by AOD extraction. A review of the literature revealed frequent misinterpretation of data on the extraction of Al from hydroxides. An approximation of the detection limit of a combination of extractions, X‐ray diffractometry, and X‐ray fluorescence spectroscopy revealed that unambiguous quantification of oxidic Al in soils of temperate latitudes is not possible because of the low contents. Therefore, we consider statements about the importance of Al hydroxides for stabilizing SOM in these soils to be questionable as long as adequate analytical technology is unavailable to identify and selectively quantify Al in poorly crystalline phases.