Mull-like Moder

Mull-like Moder is a transitional subtype between Mull humus forms and humus forms with an Oh horizon. Mull-like Moder develops predominantly on acidic topsoils and soils characterised by a low base saturation, explaining the slight bioturbation in these soils. This leads to features typical of the Ol horizon, and no biologically intermixed mineral components are observed. The litter of the Ol horizon is progressively more glued together with increasing depth, partly showing layer-like packing. Its thickness can reach 6 to 7 cm with features of a batch-like packing. The Of horizon consists mainly of needle fragments and leaf fragments. In the lower part of the Of horizon, the content of fine humus increases (Ohf horizon) and is interwoven with fine roots. Below the Of horizon, an Oh horizon occurs in patches; it is usually very thin (2–3 mm). This Oih horizon indicates an initial enrichment of fine humus covering the wavy mineral soil surface, but showing diffuse boundaries between both horizons. At forest sites, the Ah horizon is most often <10 cm thick and does not show signs of podzolisation. Thick Ah horizons can be found in soils with high base saturation, although dominated by beech litter. The boundary between the A horizon and the underlying mineral soil containing little or no organic matter is distinct or even abrupt. Distinct features of a Mull-like Moder are:
  • Ol and Olf horizon are present all year round;
  • Ohf horizon is present all year round, usually rooted;
  • Oih horizon is present; and
  • Ah horizon is present.