Organic carbon as a factor of iodine differentiation of the soil cover in the Bryansk and Oryol regions by iodine availability

Abstract

The distribution of stable iodine and humus in the upper horizon (0–20 cm) of various types of soils of the Bryansk and Oryol regions used as pastures has been studied. Soil sampling was carried out with a hand stick drill in layers in the depth interval: 0–5 cm, 5-10 cm and 10–20 cm. Iodine content was determined by kinetic rhodanide-nitrite method. Corg content was determined by the bichromate method of Tyurin. The work includes data from both long-term studies of the iodine content in the soil cover of the Bryansk region (2008–2020) and new data from expeditionary studies in the Oryol region (2022). It is shown that the soils of the Bryansk pastures are depleted of iodine and organic carbon (OC) in comparison with the Oryol region, which corresponds to the change of soil cover composition from west to east. The humus content in soils was determined and statistically significant correlation between iodine and C org. content in pasture soils were obtained (from r = 0.28 in Chernozems to r = 0.49 in Haplic Albeluvisols; in addition, for the whole sample (n = 48) the correlation coefficient ranged from 0.31 in the 0–5 cm layer to 0.43 in the 10–20 cm layer). The dependence of iodine accumulation on the OC content in different types of soils (Chernozems, Grey-Luvic Phaeozems, Umbric Albeluvisols, Haplic Albeluvisols) and their hydromorphism has been established. The identified differences in soil iodine fixation should be considered as they may influence iodine intake levels in pasture animal milk and local rations.