Humus composition and quality in anthropogenic soils of Istria

The aim of this study was to determine the composition of humus in anthropogenic soils within different agroecological conditions of Istria. The research was conducted in 2020 at three soil types: Terraced soil, Gleysol and Arable soil from Terra Rossa. Soil samples were taken from each location from the arable (0-30 cm) and subarable soil layer (30-50 cm), in 5 replications. The optical density of the alkaline extract of humic substances (E4/E6) was determined spectrophotometrically (VIS). The average content of humic acids (HA) in the arable soil layer decreased as follows: Gleysoil (0.58%) > Arable soil from Terra Rosa (0.53%) > Terraced soil (0.26%). In the subarable soil layer, the highest HA was determined in Gleysoil (0.48%), followed by Arable soil from Terra Rossa (0.40%) and the lowest found in Terraced soil (0.11%). The HA/FA in both soil layers decreased as follows: Arable soil from Terra Rossa (2.28 and 1.49) > Gleysoil (1.11 and 1.09) > Terraced soil (0.39 and 0.34). In the arable soil layer E4/E6 increased from: Arable soil from Terra Rossa (1.28) < Gleysoil (1.31) < Terraced soil (4.69), and in the subarable soil layer: Gleysoil (1.43) < Arable soil from Terra Rossa (1.64) < Terraced soil (4.83). Fulvic acids of aliphatic structure and low molecular mass, which indicate a lower quality of humus, prevailed in Terraced soil with HA/FA < 1 and E4/E6 > 4. In Gleysoil and Arable soil from Terra Rossa, HA/FA > 1 and E4/E6< 4 indicated the prevalence of aromatic, highly polymerized molecular structures, i.e. the quality of humus was better.