Annual Cycles of Carbon Dioxide Level in Soil Air

Abstract The CO 2 concentration of the gaseous phase of a silt loam soil (Udollic Ochraqualf) was studied under cultivation of wheat ( Triticum aestivum ), corn ( Zea mays L.), and soybeans ( Glycine max L. Merr.) over a 2‐year period. Disposable chromatographic tubes for direct field measurements of CO 2 in soil air were used. Dynamics of CO 2 in the soil air were observed to be conditioned by both biological and abiotic factors. Under wheat, periods of highest CO 2 concentration (6–8%) corresponded to times of intensive decomposition of plant residue within the soil profile. Under corn and soybeans, highest CO 2 concentrations were related to the periods of intensive plant growth. Soil moisture and soil temperature combined, were found to be responsible for just > 50% of CO 2 fluctuations. The influence of water tension on CO 2 in the soil atmosphere was more significant ( r 2 = 0.83) if data were restricted to that where temperature was 20 ± 2°C, and in transformations of the two parameters were used. The ln‐to‐ln dependence was linear within the limits from field capacity to wilting point. Under conditions of optimum soil water content, ln of CO 2 concentration increased linearly with ln of soil temperature within the limits of 10 to 20°C.