The research objective was to determine basic soil properties and the stability of humic acids (HAs) in individual layers of the A horizon of meadow soils. Soil samples were collected from the unique Czersk Meadow Complex in north Poland, 25 years after the end of “slope-and-flooding” irrigation that had lasted for 150 years. It is a continuation of research being carried out on the Czersk Meadows. In the previous studies (Banach-Szott et al. 2021a), continuously irrigated soils were analysed. The total organic carbon content (TOC), total nitrogen content (Nt) and grain size composition were determined in soil samples. Humic acids were extracted by Schnitzer method and analysed for: elemental composition, spectrometric parameters in the UV-VIS range and hydrophilic and hydrophobic properties. The tested soils consisted largely of sand fraction, with only small amounts of clay. The TOC, Nt and TOC/Nt ratio values all depended on soil sampling depth and distance from irrigation ditch. The TOC, Nt and TOC/Nt ratio were all highest for soils collected from a depth of 0–10 cm and for those taken 25 m from the irrigation ditch. The research revealed that the HA molecules of soils collected from a depth of 0–10 cm had higher H/C ratios and spectrometric parameters and lower values of the ω parameter and HIL/HOB ratio than those from deeper layers. This indicates that the degree of maturity of HAs increases with depth. On the basis of the obtained atomic ratios (H/C, O/C, O/H), ω parameter and spectrometric properties (A2/6, A4/6 and ΔlogK), the degree of maturity for HAs molecules was highest in the soil samples taken furthest from the irrigation ditch. The results indicate that relatively high-stability HAs were formed by the processes of transformation of the organic matter of the mineral meadow soils.