Varying amounts (0–20 meq/100g) of nitric acid were added to samples from six depths of a Maury silt loam which varied in organic matter content from 5.11 to 0.80%. Aluminum extracted by 1N KCl was found to be lower as organic matter content increased at any given pH level. This finding helps to explain the successful growth of crops in killed sods where the surface soil is acid but rather high in organic matter; it also may account for some of the benefit of organic amendments on acid soils.