A potential level of agricultural productivity of formerly arable soils was assessed in a case study within the Poshekhonsky District of the Yaroslavl Oblast, Russia, with the use of an actualized soil-ecological index (SEI). This index showed low and medium fertility levels in most of the studied arable soils during the period of 1988-1990, which was followed by agricultural abandonment of many arable lands. The re-assessment of post-arable varieties of the same soils in 2019 allowed us to identify multidirectional trends of evolutionary changes in soil properties over the three decades. Post-arable soils on loamy parent materials were characterized by the development of stable hydromorphic features, dehumification, a sharp decline in the supply of available nutrients and occasionally an acidification of humus horizons, which was reflected in the reduction of SEI values by 1.1-1.9 times over the study period. Post-arable sandy soils, on the contrary, were characterized by a predominance of progradation processes associated with increasing humus contents and decreasing acidity levels. The post-agrogenic evolution of soils including the development of new soil properties should be taken into account in agroecological assessments and prognoses of the agricultural production potential of soils under conditions of changing climate.