Redoximorphic features as indicators of soil water regime

Soil water regime, as one of the key components of soil fertility, refers to the quantity, retention, and movement of soil water. Rather than through expensive and/or time-consuming measurements, it can be assessed from the fieldobservable morphological properties in the soil profile. Excessively wetted soils have a specific morphology, and are therefore often referred to as hydromorphic. Their morphology is caused by various soil redoximorphic features (RMFs), resulting from the reduction, translocation, and oxidation of iron and manganese oxides. Hydromorphic soils largely comprise Gleysols and Stagnosols (along with Gleyic Fluvisols) that are excessively wetted by groundwater, precipitation and/or flooded water. Their morphology is often described/analyzed with different terms/criteria in line with their global distribution. This complicates the comparison and classification of such soils and thus their use or reclamation. This review paper describes and compares common RMFs and explains their formation. It then proposes the revised Croatian terms for these features, which are in line with the terms used in the international soil classification systems of WRB and/or Soil Taxonomy. Furthermore, the criteria/rules used for diagnosing RMFs when classifying hydromorphic soils are critically reviewed. Finally, it is shown that a methodologically sound RMFs description can provide a quick insight into the crucial soil water regime parameters, such as location and duration of soil saturation, the origin of the excess soil water, recentness of excessive soil wetting, etc. However, depending on the research objectives and/or actual soil conditions, field soil description cannot always fully replace continuous field monitoring of the soil water regime and/or laboratory and micromorphological soil analyses.