Soil cover of Baikal area is presumably presented by heavily textured calcareous soils. They are formed on various elements of relief under canopy of dark-coniferous and small-leaved forests and more rarely under meadow and steppe herbs. Soil-forming rocks are sandy loamy and loamy alluvium and eluvio-deluvium of rocks of different colours with prevailing calcareous shists.

Humus formation takes place under drastic ecological conditions: sharply continental climate, poor floristic composition as main source of humus. Soils are, howevcer, rich in humuc. Its content in virgin lands varies within the limits of 4-10%, in arable analogues within the limits of 2-6%. Under taiga vegetation humus content is considerably lower and ranges from 2 to 4%. The reason of elevated humus content lies in the fact that because of prolonged period of seasonal frost and orrurence of permafrost the removal of plant decomposition and humification products from soil profile is restricted.

Humus profile is characterized by accumulation of humus in upper part ( up to 80% is concentrated in the layer of 0-20 cm) and sharp depthwise decrease. Futhermore, calcareous nature of rocks and their weathering products favour to fixation of humus acids within the limits of soil profile.

The nature of humus acid is distinguished by specific features. Thus, up to 50% of soil humus is composed by fulvic acids, and up to 30% by humic acids. In these conditions one should expect higher retention of humus in soil profile, but this is not observed because of low rate of weathering of calcareous rocks, as the admixturess are present here of highly dispersed mineral of silicate group and dolomite which is less soluble as compared to calcite. That is why humus acids are not completely neutralised by weathering products, besides newly formed humic acids are hydrolysed up to fulvic acids under influence of high moisture and percolative water regime.These are the reasons of fulvic acids prevalence.

In the soils under research both humic and fulvic acids, their calcium salts especially, are closely allied by elementary composition, dispersion degree and light absorption in visible part of spectrum. The H:C ratio greately exceeds the value of 1 that is a formal evidence of prevalence of aliphatic structures in their molecules. The friable structure of humic acids and fulvic acids especially is confirmed by their difficult precitability on addition of electrolite, calcium chloride for example. It was shown that under prolonged soil use in agriculture the ratio of humic and fulvic acids is left practically unchanged.

Boris M. Klenov
Institute of Soil Science and Agrochemistry
Siberian Branch of the Russian Academy of Sciences
Sovietskaya St 18
630099, Novosibirsk, Russia
Telephone: (3832) 225840                                 .
Fax: (3832) 225 665
E-mail: soil@issa.nsk.su