The aim of our paper was to determine the properties of humic acids produced as a result of decomposition (under controlled conditions) of post-harvest residue of maize, rapeseed, and sunflower in different soil types (haplic luvisol, chernozems, haplic arenosols, and haplic gleysols). The extraction of humic acids was performed from the samples obtained directly once the post harvest residue was mixed with soil material, and after 360 days of incubation. The properties of humic acids were determined based on elemental analysis HPLC and HPSEC. The qualitative parameters of humic acids demonstrated that introducing sunflower postharvest residue into the soil causes the formation of humic acids typical for soils without any additives. On the other hand, properties of humic acids after introducing maize post-harvest residue into soil are most modified.