Soil microbial biomass and its activity in seasonally frozen soils in the Middle Ob region
M.V. Jakutin

The influence of flood condition on C and N microbial biomass (fumigation-incubation method); on the size and the part of active biomass (Werf and Verstraete method, 1987) and on respiration were appreciated in alluvial meadow and meadow-swampy soils annually flooded by waters and in non-flooded alluvial soddy and zonal sod-weakly-podzolic soils in the Middle Ob region near Tomsk (Western Siberia). In October 1991 before the freezing of soils and in June 1992 after the thawing and ending of the flood the samples of the upper layer of soils were analysed.

In the series of soils: sod-weakly-podzolic - soddy - meadow - meadow-swampy soils the increasing of hydromorphy takes place; and in this series (October) the increasing of C biomass (from 24, 55 and 92 to 150 mg/100 g soil accordingly), N biomass (from 5, 11 and 20 to 32 mg/100 g soil accordingly) and active biomass (from 1.0, 4.1 and 4.4 to 5.7 mg/100 g soil accordingly) is marked. The part of active biomass in this series of soils is 4.1, 7.6, 4.7 and 3.8% accordingly, and respiration is 15, 10, 20 and 53 mkg C-CO2/g soil during the day accordingly. By June the increase of all investigated parameters occurs: the size C biomass is increased by 60, 32, 51 and 44%, accordingly; N biomass - by 55, 23, 37 and 29%, accordingly; the size of active biomass - by 81, 65, 63 and 47%, accordingly, and respiration - by 43, 25, 60 and 58%, accordingly. The part of active biomass is considerably increased in nonflooded zonal sod-weakly-podzolic soil up to 8,6% and in alluvial soddy soil up to 14,8%, and slightly increased in flooded alluvial meadow soil up to 6,4% and in meadow-swampy soil up to 4,0%.

Thus, alluvial soils constantly flooded by waters are characterised by constantly higher microbobiomass and respiration, than those which are non-flooded, but the part of active biomass in them is on the whole lower. 

Mikhail V. Jakutin
The Institute of Soil Sciences and Agrochemistry SB RAS
Sovetskaja st.,18
Novosibirsk, 630099, Russia
(383-2)-22-54-15
fax:(383-2)-22-56-65
E-mail: soil@issa.nsk.su