CONCENTRATION-DEPENDENCE OF CO2 EVOLUTION FROM SOIL IN CHAMBER WITH LOW CO2 CONCENTRATION (LESS-THAN 2,000 PPM), AND CO2 DIFFUSION SORPTION MODEL IN SOIL

Concentration dependence of CO2 evolution from soil was studied under field and laboratory conditions. Under field conditions, when the CO2 concentration was measured with an infrared gas analyzer (IRGA) in a small and column-shaped chamber placed on the ground, the relationship among the CO2 concentration c (m3 m-3), time t (h), height of the chamber h, a constant rate of CO2 evolution from the soil upsilon (m3 m-2 h-1), and an appropriate constant k, was expressed by the following equation, dc/dt = upsilon/h-k(c-a) (c = a at t = 0). Although most of the data of measured CO2 evolution fitted to this equation, the applicability of the equation was limited to the data to which a linear equation could not be fitted, because the estimated value of v had a larger error than that estimated by linear regression analysis, as observed by computer simulation. The concentration dependence shown above and some other variations were analyzed based on a sorption/diffusion model, i.e. they were associated with CO2-sorption by the soil and modified by the conditions of CO2 diffusion in the soil.