Development of organic matter in soils of natural phytocoenoses and agrocoenoses

Abstract

The brown mountain carbonate soils covering the “yadiere” (hills) in the Gissarska valley of Tadzhikistan have relatively high humus portions. The humus content in the upper layers of sedentary soils was found to range from 2.70 to 3.18 per cent. However, in eroded soils the humus content declines from 1.35-0.83 per cent to levels as low as 0.57-0.75 per cent. The decrease of humus substances in erodible soils is mainly dependent on their slope exposure. Soils on sites sloping to north revealed the highest humus content whilst soils on east and west slopes and, in particular, on south slopes were found to have the lowest humus content.
Sprinkler irrigation applied to soils on sloping sites, following grass seeding, was found to result in swift growth and in the evolution of a natural flora what, in turn, induced intensive humus build-up. The humus content of the covering layer increased by 0.98 per cent, that in eroded soils markedly less. The increased humus content primarily leads to humic acid enrichment, this effect causing a wider SGK:SFK ratio.
Following grass seeding on these soils a marked increase in the content of dissolved and R₂O₃-bound humic acids can be observed.