Raw Humus

Raw humus (also referred to as mor humus) consists of scarcely decomposable plant residues (litter) and represents the most unfavorable humus form. Poor decomposition of plant waste is attributed to a too cool or humid climate. The litter of conifers are more difficult to decompose than the litter of many deciduous trees. Since components such as waxes, resins, tannins and lignin are usually harder to disintegrate, dead plant residues with high proportions of these substances are preserved much longer and often only form inferior humus. The undecomposed litter material and the few organic fine substances are clearly separated from each other. The humic substances from the topsoil can be washed further into the sub-floor (B-horizon). Moreover, the poorly decomposed litter of a raw humus soil can form organic acids. As a result, the iron in the soil is increasingly able to migrate and can also be washed into the B-horizon. Raw humus thus promotes podsolation.