Humus forms in the proposed Soil Classification System of Slovakia

Abstract

In forest ecosystems, the surface organic layer plays a significant diagnostic role. Nutrient availability, soil biological activity, water retention, and carbon sequestration are closely related to its qualitative and quantitative properties. Therefore, properties of the surface organic layer belong to the key indicators for assessing ecosystem functioning and resilience. In Slovakia, the classification of humus forms is an integral part of the Morphogenetic Soil Classification System (MSCS) of Slovakia. The recent update to the MSCS therefore also includes revisions to the classification of surface organic layers and humus forms, with an emphasis on clearer terminology and improved compatibility with international classification systems. The aim of this paper is to highlight the updated status of surface organic layer classification and the changes compared to the previous version. Unlike the previous version of the MSCS from 2014 y, which used a three-level hierarchy (horizon, subhorizon, variety) for classification, the updated version distinguishes only between horizon and variety. In total, there are 7 horizons – 5 horizons of the aerobic conditions (litter, fragmented, humificated, rhizic, and anthropogenic) and 2 horizons of the anaerobic conditions (peat and humolite). Compared to the previous classification, new varieties were added: bryoic, lignic, and mycogenic. Four terrestrial humus forms were identified for conditions in Slovakia: mull, moder, mor and tangel. In addition to the typical humus forms, transitions to other forms and subforms exhibiting signs of periodic waterlogging were identified. In the updated classification, the humus forms were supplemented with the subforms: rhizic, lignic, and bryoic.

Keywords: surface organic layer, litter horizon, fragmented horizon, humic horizon