mulljorden

Mulljorden is a term used in Nordic and broader European soil science to describe a mull-type humus form in mineral soils. It denotes soils where organic matter from the litter is rapidly decomposed and mixed into the mineral soil, creating a humus-rich but relatively well-integrated upper horizon. This contrasts with mor or moder humus forms, where the organic layer remains more distinct, less mixed, and more acidic.

Formation and characteristics. Mulljorden forms under favorable climate and vegetation conditions, typically in deciduous or mixed forests with prolific litter input and active soil fauna, especially earthworms. The result is a topsoil horizon in which organic matter is evenly mixed with mineral material, producing a relatively thick, fertile A horizon with high biological activity. The organic layer is less distinct than in mor soils, and the pH is often near neutral to slightly alkaline, with high base saturation and available nutrients such as calcium, magnesium, and potassium. Soil structure tends to be good, promoting root penetration and drainage.

Distribution and ecology. Mulljorden occurs across temperate regions of Europe and North America under deciduous and mixed forests. It is associated with sites that experience sufficient moisture and temperature for rapid litter decomposition and intense soil biota activity. The form supports vigorous tree growth and productive forest soils, but is sensitive to acidification and disturbances that reduce fauna activity or alter litter input.

Comparison and management. Compared with mor soils, mull jords are typically more fertile, have a thinner or less visible organic surface, and show stronger mixing of organic matter into the mineral soil. Management emphasizes maintaining nutrient supply and avoiding practices that disrupt soil fauna or overacidification to preserve the mull characteristics.