a forest humus type, transitional between mull and mor, characterized by an accumulation of organic matter on the soil surface in friable Oe horizons, reflecting the dominant zoogenous decomposers —note 1. duff mulls are similar to mors in that they generally feature an accumulation of partially- to well-humified organic materials resting on mineral soil, and similar to mulls in that they are zoologically active —note 2. a duff mull usually has four horizons: Oi (L), Oe(F), Oa(H), and A —note 3. duff mulls are sometimes differentiated into the following groups: mormoder, leptomoder, mullmoder, lignomoder, hydromoder, and saprimoderThis definition last updated 07/30/2008