Re: O horizon and soil function

Unless you want to restrict the highest rating to include only soils with the greatest inherent ability to perform this function, I see no compelling reason to restrict the rating of 1.0 to Histosols. You state that your observations suggests that as little as 4 cm is typically present on soils that are functioning at a ""high level"", so maybe that is good enough for your purpose. However, I wonder whether it is a bit of an oversimplification to consider only organic thickness for this function. It seems to me that you need to also integrate texture and maybe bulk density or porosity into this rating. Wouldn't a loamy or sandy soil with a 4 cm organic surface function as well or better than a clayey soil with a 6 cm organic layer - at least in terms of the transmission of water into the soil profile? Organic thickness alone may be more indicative of the level of function for detoxifying chemicals or cycling nutrients.