Microcalorimetric evaluation of soil microbiological properties under plant residues and dogmatic water gradients in Red soil

Abstract

A study of 6 months duration was carried out to investigate the effect of water regimes and organic amendments on the soil microbial biomass and microbial population under Red soil collected from Hunan 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 soil microbial activities. We observed that the use of GM exhibited more 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 and Q were 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 of microbial community shifts and activities in soil ecosystems.