Another issue that needed delving into, brought to our attention by one of our diligent readers:
“Loam is a classification given to soil that contains relatively balanced amounts of sand, silt and clay. Loam soils typically contain less than 52 percent sand, 28 to 50 percent silt, and between 7 and 20 percent clay. Classification as a loam soil has nothing to do with the organic material it contains or where it is found. A mixture that contains almost equal amounts of silt, sand and clay is referred to simply as loam. However, if the soil has slightly more of one of these elements in relation to the others, then the classification is modified to sandy loam, clay loam, silt loam, sandy clay loam, or silty clay loam.”
Leave it to the Oregon State Forestry people to set things straight:
Humus: Total of the organic compounds in soil exclusive of undecayed plant and animal tissues, their “partial decomposition” products, and the soil biomass. The term is often used synonymously with soil organic matter.
Mor: A type of forest humus characterized by an accumulation or organic matter on the soil surface in matted Oe(F) horizons, reflecting the dominant mycogenous decomposers. The boundary between the organic horizon and the underlying mineral soil is abrupt. Sometimes differentiated into the following groups: Hemimor, Humimor, Resimor, Lignomor, Hydromor, Fibrimor, and Mesimor.
Mull: A forest humus type characterized by intimate incorporation of organic matter into the upper mineral soil (i.e. a well developed A horizon) in contrast to accumulation on the surface. (Sometimes differentiated into the following Groups: Vermimull, Rhizomull, and Hydromull).
Duff Mull: A forest humus type, transitional between mull and mor, characterized by an accumulation or organic matter on the soil surface in friable Oe horizons, reflecting the dominant zoogenous decomposers. They are similar to mors in that they generally feature an accumulation of partially to well-humified organic materials resting on the mineral soil. They are
similar to mulls in that they are zoologically active. Duff mulls usually have four horizons: Oi(L), Oe(F), Oa(H), and A. Sometimes differentiated into the following Groups: Mormoder, Leptomoder, Mullmoder, Lignomoder, Hydromoder, and Saprimoder.