Carbon input and balance in soils is regarded as the main criterion of agricultural sustainability. Generally, carbon dynamic depends not only on the carbon input and its decomposition rate, but it is also influenced by various agronomic practices. Therefore, changes in organic carbon stock and humic substances quality were evaluated in two different agricultural management systems (permanent grassland and intensive crop sequences). Haplic Cambisol (Czech-Moravian Highland, locality Vatín, Czech Republic) was sampled twice a year (spring and autumn) in the depth 0-20 cm during the period 2010-2016. Soil was sandy-loam textured, with middle organic carbon content and very low humic substances quality. Results showed that crop management practices directly influenced soil cumulative potential, quality of humic substances, soil reaction and amount of nutrients. Statistically significant differences were found.