Extraction of Phenolic Compounds From Soils.

Understanding the composition and amount of phenolic inputs from plants is important for studies of soil organic matter formation and nutrient cycling. However, some phenolic compounds, including tannins, can sorb or complex with the soil making them difficult to extract. We extracted soils with a variety of solvents including water, aqueous acetone, and acidified methanol (AM), and measured recovery of total (TP) and protein precipitable phenolics. These studies suggested the amount of TP extracted varied with solvent.  Comparatively little TP was extracted by water while AM appeared to be the most efficient solvent.  The amount of TP extracted from soil was relatively low and varied with land-use, depth, and time of year. In contrast, large amounts of polyphenolics are obtained from plant tissues including leaves and bark by extraction with aqueous acetone.  The results of the soil studies must be interpreted in the context of possible interference in the TP assays by other oxidizable components of soils, including iron (II) and oxidizable organics that are not phenolic.  In some experiments,  tannin extracted from soil retained the ability to precipitate protein, providing a more selective measure of tannin recovery than total phenolics analysis.  We conclude that phenolics extracted from the soil matrix with acidified methanol can be useful to identify differences among treatments.  Further research is required to develop a means for distinguishing between phenolics from plant inputs and those that are the products of decomposition or an artifact of other oxidizable compounds in soil.