Chamber Method for Measuring CO2 Flux from Soil Surface

• Published in: Journal of Agricultural Meteorology Vol. 42; no. 3; pp. 225 - 230
• Main Author: INOUE, Kimio
• Format: Journal Article
• Language: English
• Published: Tokyo The Society of Agricultural Meteorology of Japan 1986; Japan Science and Technology Agency
• ISSN: 0021-8588; 1881-0136
• DOI: 10.2480/agrmet.42.225

To establish a method for measuring CO2 flux from soil surface, the relation between CO2 flux and the ventilation rate of a chamber was studied for the four different soils such as Andosol, Brown Lowland soil, Gray Lowland soil and Sand. The CO2 concentration in the air at the inlet and the outlet of the chamber was determined with an infrared gas analyzer (see Fig. 1). CO2 flux from soil surface was calculated from the CO2 difference between the inlet and outlet of the chamber and the air flow rate. 1. It was found that the CO2 flux for the soils increases gradually with increasing the ventilation rate, approximating to respective constant levels at the higher ventilation rate. The critical ventilation rates at which the respective CO2 flux are assumed to approach to constant levels were about 13 times/hr for the Andosol and about 9-13 times/hr for the other tested soils. 2. One dimensional CO2 balance equations for soil layer and a chamber were solved to derive the relationship between CO2 flux and the ventilation rate, and to obtain CO2 profile in the soil layer. The derived relationship indicates that CO2 flux is affected with effective CO2 gas diffusivity in a soil layer and ventilation rate (see Fig. 4). The theoretical results agreed well with the experimental results presented in Figs. 2 and 3. 3. The experimental results obtained using the CO2 chamber system and Eqs. (5) and (6) were used to calculate the average effective CO2 gas diffusivity over the soil layer with 15cm depth and the CO2 concentration at the bottom of soil layer and results obtained are shown in Table 1. Under flooded conditions, the effective CO2 gas diffusivity for the tested soils was over a range from 0.035 to 0.042cm2s-1. These values were lower than molecular diffusivity of CO2 in the air. 4. The chamber method was applied to measurements of the CO2 flux at the soil surface of three rice plant fields. CO2 flux measurement was made together with measurements of microclimatic elements during the period of rice cultivation in 1984 and 1985. The results are shown in Fig. 5. The daily CO2 flux was higher for a rice field with the application of organic manure than without that. It was found that CO2 flux at the rice field decreases gradually with lowering of soil temperature.