A method for quantifying rates of O-2 consumption and CO2 production in soil

Considering the soil as a heterogeneous bioreactor, a method is developed t hat permits a quantitative evaluation of O-2 and CO2 levels in the soil atm osphere. Mathematical modeling allowed us to quantitate the rate at which s oil consumes O-2 or produces CO2 under close-to-field conditions. Values of qCO(2) and qO(2) ranging between 0.2 and 8 kmol CO2-C ha(-1) day(-1), and 0.4 to 35 kmol O-2 ha(-1) day(-1), respectively, were measured in a soil re cently subjected to agriculture in the El Salado river basin (Buenos Aires, Argentina). The mathematical model discriminates between purely physical ( diffusion, advection) and biological (e.g,, microbial activity) processes. The gas measurements were sensitive to the crop stage in a soil recently su bjected to agriculture. We conclude that qO(2) reflects more accurately tha n qCO(2) the contribution of microbial activity to the rate of gas exchange s in soil. Results are discussed in terms of soil biogeochemical processes.