Increasing SOC is a good thing: promoting soil aggregation, nutrient availability and C sequestration. Often promote water holding capacity. so when i am asked When is the CO2 evolution rate in compost be considered on the basis of total solid and organic matter? i will say it is based on the amount of soil moisture or amount of water in the soil. on that CO2 evaluation rate can be based on total solid and organic matter but all is based on the porosity (the air space)

i hope it helpful?

Thanks Godwin Sabah for your explanation. But, what I am referring is that, I am determining CO2 evolution rate in compost as a parameter for compost stability. There are two units of CO2 which :

1- mg CO2- C per g OC per day

2- mg CO2- C per g TS per day

but do not know exactly what is the difference between two units.

Solvita has a compost maturity assessment. The compost is considered mature and stable when ammonia and carbon dioxide levels are low.

CO2 evolution test. Using a simple respirometric instrument (Fig. 2) 41, the 10 fast compost samples, 10 test-kosi samples, 10 farmer-kosi samples, and 10 household wastes samples were incubated at 30 °C for 21 h in the glass fask (Fig. 2), and CO2 produced was determined. A 0.5 g air-dried sample was mixed with an air-dried 10 g arada soil collected from the mid-altitude dry sub-area and water (60% soil water saturation). A small container that contained a 2 g sodium hydroxide (carbon dioxide absorbent) was placed in the fask. Te volume of water sucked by the measuring pipette was measured. From the volume of water measured, the volume of water measured at the control treatment (only the culture soil) was subtracted to obtain the volume of CO2 produced. CO2 evolved is soluble in aqueous solutions, and the solubility is pH-dependent9 . Tus, the original pH of each sample was determined. Calcisols42 (Endopetric Hypercalcic Calcisol; clay loam) were typical soils in the arada felds in the mid-altitude dry sub-area26.

Kindly use this paper

https://www.nature.com/articles/s41598-021-83611-4.pdf?origin=ppub

I think that the first formula expresses the quantity of CO2 compared to the organic matter (OC) and the second compared to the dry matter of the compost (TS: total solid). But, but, logically the values ​​must be reversed (2 mg CO2- C per g OC per day ;

1 mg CO2- C per g TS per day)

I agree with the answer of Harraq Ahmed.

Thanks for your help.