Humus quality in Terrra rossa soils under olive groves with different soil management types

The paper aimed to determine humus quality in Terra rossa soils under olive groves with different soil management types. A total of 10 top-soil samples (0-20 cm) were collected in olive groves of Middle Dalmatia, Croatia, out of which 5 were from the traditional low-input olive groves (TOG) and 5 in the intensive olive groves (IOG). The soil samples were analyzed for basic soil properties, soil organic carbon (SOC), and fractional composition of humic substances. Spectroscopic characterization of humic substances was carried out by measuring absorbance in the VIS spectral range (400-700 nm). Optical index E4/E6 (ratio of optical absorbance at 465 to 665 nm for humic substances in solution) was calculated. The mean value of SOC in soils under TOG (3.06%) was lower than in soils under IOG (3.88%). Higher variations of carbon in humic (CHA) and fulvic acid (CFA) were observed in the soils under IOG. The mean CHA/CFA ratio in soils under TOG was higher than in soils of IOG (1.78 and 1.26, respectively). The soils under TOG had fulvic-humic to humic types, while the soils of IOG had humic-fulvic to humic types of humus. A lower mean E4/E6 index of soils under TOG than IOG (3.78 and 4.36, respectively) confirmed the results of the classical analytical method. Our findings reveal higher variation and lower humus quality in soils under intensive olive cultivation.