Agriculture Reference
In-Depth Information
twice as high as the May minimum. In cultivated soils at Kjettslinge (Sweden), season-
al variation of total biomass was much smaller with a difference of 25 % between the
minimum value in June
and the August maximum
(Schnürer
et al.,
1985).
Kilbertus
et al.
(1982) observed quite large variation in the bacterial population
density of the top few centimetres of the A horizon of a conifer forest: the maximum
density, in June, was nearly 100 times greater than the minimum in December. The pro-
portion of bacteria protected in microaggregates (released by sonication of the soil
samples) varied greatly over the year, with minimum values in the middle of the year
and maximum in winter (Figure III.11). A similar pattern was observed in an adjacent
deciduous forest with a lesser proportion of protected micro-organisms (40 % on aver-
age compared with 58 % in the coniferous site).
Several studies of fungal populations in temperate forests have revealed some
significant seasonal variation in the relative abundances of species in microfungal com-
munities (
e.g
., Bissett and Parkinson, 1979; Widden, 1986). In volcanic soils on slopes of
