Barratt: Mull and Mor Development in Temperate Grasslands Factors of Mull and Mor Development in Temperate Grasslands

Grassland humus forms have been investigated morphologically in the field and with the microscope (Barratt 1960, 1964). They are divisible into two main groups: mulls and mors. In mulls, organic residues are finely conllninuted and intimately mixed with the colloidal-sized fraction of the mineral soil. In mors, organic residues accumulate predominantly above the mineral soil surface, but show progressive decomposition with increasing proximity to the mineral soil, and typically three layers are produced.