Pyrogenic transformation of the phosphate state of permafrost forest soils of Central and Southern Yakutia

Abstract

For the first time, the phosphate state of permafrost forest post-pyrogenic polycyclic soils of Central and Southern Yakutia, formed respectively in arid and humid climates, was studied and evaluated. These soils with a polycyclic profile, formed in the transaccumulative facies of this regions of the permafrost zone, contain, in addition to the modern one, 2–3 buried humus horizons with abundant inclusion of black charcoal. These pyrogenic humus horizons are characterized by an increased content of humus, total nitrogen and phosphorus soluble in iron oxalates, exchange bases, as well as fractions of physical clay and silt compared to neighboring mineral horizons of the soil profile. At the same time, the brown soil of Southern Yakutia, formed under less severe and humid climatic conditions, compared with those of the pale soil developed under cryoarid conditions of Central Yakutia, was more biogenic, and the total content of phosphorus here was 98.0–427.2, whereas in the second soil – only 11.0–257.1 mg P2O5/100 g of soil. Organophosphates predominated in the composition of the total phosphorus of burozem, amounting to 51.8–81.3%, and in pale soil – mineral forms of phosphorus, which accounted for 52.2–78.8%. The fractional composition of mineral phosphates of both types of permafrost soils was mainly dominated by phosphates of one and a half oxides (Al-P and Fe-P), totaling 43.3–94.3%, and among the latter – Fe-P, which accounted for 34.8–87.4% of the total amount of all fractions of mineral phosphates. It is assumed that the high content of iron phosphates, and in some cases occluded aluminum-iron phosphates in the studied permafrost soils, is due to the manifestation of both cryogenic and biogenic pyrogenic ferruginization in their genesis.