Geography of Soils Deptt., Moscow State University, Moscow, U. S. S. R.
*Present address: Central Arid Zone Research Institute, Jodhpur, Rajasthan
Four profiles representing soils developed under natural vegetation in different altitudinal belts were analysed for group and fractional composition of humus according to Tyurin's scheme as modified by Ponomor'ova. The results show that the humus in high altitude soil profile is overwhelmingly fulvic with fractions associated with free sesquioxides predominating. Further the humic acid molecule has a low degree of condensation and thus is close to fulvic acid. The humus in middle altitude soil profile is less fulvic and it shows an increase in fractions associated with divalent cations. Fulvic acid fraction associated with highly mobile sesquioxides decreases considerably and humic acid molecule becomes more condensed. This trend is not maintained in lower middle altitude profile whereas in low altitude profile humus becomes exceptionally humic with fractions associated with divalent cations dominating. The peculiarity of the last two soil profiles seems to be conditioned largely by the associated vegetation which is Pinus roxburghii in one case and deciduous bush in the other.
Humus fractionation, soils of Himalayan belt, relief factor
