A study of 6 months duration was carried out to investigate the effect of water regimes and organic amendments
on the soilmicrobial biomass and microbial population under Red soil collected fromHunan Providence, China. The soil microbial biomass and population were measured with traditional methods and results obtained by
conventional methods, corroborated with microcalorimetry. The incorporation of rice (Oryza sativa L.) straw
(RS) and green manure (GM), especially at high rates, enhanced the soilmicrobial activities.Weobserved that the
use ofGMexhibitedmore significant stimulating effects on microbial activities than RS. Similarly, water regimes,
25% (W1) and 200% (W2) of water holding capacity, also had significant effects on microbial activities.
Comparing the effects of water levels, we noticed that W2 had a significant negative influence on soil microbial
biomass and population. To compare the results of conventional methods and to check the sensitivity of
microcalorimetry, the thermodynamic parameters, microbial growth rate constant (k), total heat evolution
(Q), peak height (Pmax) and peak time (tmax) were calculated. Highest Pmax, k and Q were observed in GM
treatments at water regime W1, while highest tmax values were recorded in CK (control) and RS treatments at
W2. The microcalorimetric parameters, Pmax, k andQwere positively correlated, whereas tmax negatively linked
with microbial biomass and population at p < 0.01. Our results suggest that microcalorimetry successfully verified the results obtained from customary methods and microcalorimetric parameters Pmax, tmax, Q and k proved that they are highly sensitive to microbial properties and could be used as indices ofmicrobial community shifts and activities in soil ecosystems.