Both dehydrogenases and soil respiration (CO2) mostly used as indication or measure to metabolic activity of microorganisms in soil or compost. I am asking whether it is necessary to estimate the both parameters or it is sufficient to estimate either of them as an estimation of microbial activity in soil or organic matter?
Any enzyme measurement to monitor microbial activity is an 'indirect' method to monitor specific microbial activity (e.g. urease, denitrification enzyme activity (DEA) and dehydrogenase). Most extracellular enzymes (secreted outside the cells) are captured in soil colloids and can accumulate over time hence the amount of enzyme activity may not reflect the actual microbial activity or microbial counts. Dehydrogenase activity method is widely used since it measures intracellular enzyme activity. However, its coverage of the wide spectrum of all microbial species is not fully known.
On the above basis, measuring CO2 may provide more accurate indication of the overall heterotrophic microbial activity in unsaturated soils.
In the case of compost, depending on the composting stage, CH4 could also be emitted from the anaerobic process hence CO2 may not provide the full picture. If composting process has been fully completed, CO2 may be used as a sole indicator.
Considering the kinds of indicators ( physical, biological and chemical ) inassessing soil health would be safer than using only one kind of attribute. Measurement of soil biomass already give an indication of the potential microbial activity. However , the actual and expressed activity is important to assess as well. Especially some biolgical soil quality indicators like B - glucosidase, B- glucosamidase ans`dehydrogenase, these can be linked to particular soil functioning measures: corbon minerilisation and disease suppresiveness.
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