Abstract
By using a multiplex microcalorimeter, growth thermograms were obtained by continuous monitoring of heat evolution associated with microbial degradation of glucose for Gray Lowland soil, Low-humic Andosol and Cumulic High-humic Andosol, all of which were collected from experimental plots with and without straw compost long-term application. 1) The growth rate constant (μ) the doubling time of cell division time (t_D), the peak time of thermograms (t_P) and the glucose efficiency (G. E.) were determined by kinetic analysis of the growth thermograms for all of the soils. 2) The growth rate constant (μ) was larger for the Gray Lowland soil than for the Humic Andosols and a reverse relation was observed for the doubling time of cell division (t_D), which was the smallest for the Gray Lowland soil and the largest for the Cumulic High-humic Andosol. Under straw compost long-term application, the growth rate constant of Humic Andosol changed slightly, but hardly changed in Gray Lowland soil. 3) The peak time of thermograms (t_P) was longer for the Humic Andosol than for the Gray Lowland soil and became shorter with the long-term application of compost in all of the soils. 4) The glucose efficiency (G. E.) was almost constant for all the soils and was between 60 and 70%. 5) The calculation using the formula proposed by Konno showed a high linear correlation between the ratio of microbial population (n_0/n_0^0) and the amount of glucose added in pre-incubation (S). 6) The microbial population index (n_0^0/k) estimated from Konno's formula varied with soils and increased with the long-term application of compost in all of the soils. This index could be considered to be a suitable value for evaluating the amount of soil microbial biomass.
