Description of terms used in humus form systematics

Term Description
Soil-forming Conditions
aeromorphic Morphology indicating soil development under well-aerated topsoil conditions
aero-hydromorphic Morphology indicating soil development under moderately aerated or poorly drained topsoil conditions
hydromorphic Morphology indicating soil development under predominantly water saturated topsoil conditions
peat formation Peat formation is the result of incomplete decomposition of the remains of peat-forming plants induced and controlled by conditions such as waterlogging, low oxygen supply, low nutrient availability, or low litter decomposability.
peat-forming plants,
peat-forming vegetation
Plants which are peat-forming under hydromorphic conditions, for example: sphagnum moss, different carex species, different species of the sedge family
cultitropic Anthropogenic—substantial changes of the nutrients and the base saturation, soil structure due to regular fertilisation and sometimes tillage
Humus form
humus form Order of distinct units defined by organic surface horizons and the first mineral horizon with similar morphology, depths and type of boundary of horizons indicating specific conditions for bioturbation, decomposition, humification, and mineralisation.
master horizon Horizon with an important and dominant soil genetic process such as peat forming or podzolisation, for example: O, H, A, S, G, D, R
mineral master horizon Master horizon with a content of organic carbon < 15% mass (A, B, C, G, S)
mineral topsoil Soil layer at the soil surface, with an organic carbon < 15% mass
modified horizon Horizon with a dominant and a subdominant soil genetic process, such as Ohf, an Of horizon with 30–70% volume of organic fine material
organic master horizon Master horizon with a content of organic carbon ≥ 15% mass (O, H, U)
organic surface layer Sum of all macroscopically visible distinct organic material characterised by texture and packing of the organic material overlying the mineral soil. Layers may vary in percentages of macroscopically visible plant residues and organic fine material
organic surface horizon Organic horizon at the surface of soils (O, H or U horizon)
soil horizon Soil area which summarises common features as a result of soil forming processes
topsoil All soil layers (organic surface layer and top mineral soil) comprising the humus form. At forest sites, the term forest floor is often synonymously used
transition horizon Soil horizon with two or three important soil genetic processes, for example Ah-Go (humus accumulation and groundwater influence, typical of transition soil types)
Processes and properties of
organic matter
degree of decomposition and humification Deduced by the percentage of macroscopically recognisable plant residues and organic fine material in the peat. Ranging from H1 (plant structures completely visible) to H10 (100% organic fine material)
humus All organic matter on the soil surface and within the soil, comprising dead plant, microbial, or faunal residues and their transformation products
humification Processes of decomposition and humification of plant material via hydrolysis or oxidation and reduction mediated by soil organisms, resulting in a continuum of organic material (plant, microbial, and faunal metabolites) of various molecular sizes and composition.
organic fine material Dark-coloured, amorphous organic matter, without macroscopically recognisable tissue structures occurring in the organic surface layer, peat or mineral soil
packaging and structure of O material Describes how units of the O layers are interconnected
peat Accumulation of plant material under anaerobic conditions. Plant material varies in the degree of decomposition and humification