This article analyses relationships between soil erosion severity and soil organic matter (humus) content. The paper describes approaches to assess cumulative soil loss due to the combined action of natural (geological) and accelerated (human induced) soil erosion on Eutric Albeluvisols in Lithuania. Evaluation of soil erosion severity helps us understand which segments of the landscape are susceptible to erosion and therefore require soil conservation. The study also evaluates changes in soil organic matter content in relation to erosion severity. Factors considered in evaluating soil erosion severity included the existing genetic soil horizons remaining after soil erosion processes, the estimated thickness of lost soil and slope inclination. The estimated depth of soil loss due to the combined action of natural and accelerated soil erosion varied from 0.1–0.8 m on the undulating topography of the Žemaičiai Uplands. Erosion rates increased with slope steepness. Therefore, natural soil fertility (as indicated by spring barley yields) decreased by 21.7, 39.7 and 62.4% on slopes of 2–5°, 5–10° and 10–15°, respectively, compared with flat land. Crop yield was strongly negatively correlated (r2 = 0.790, P < 0.001, n = 138) with erosion severity and strongly positively correlated (r = 0.922; P < 0.001, n = 80) with soil organic matter content
