A method for quantifying rates of O2 consumption and CO2 production in soil

Considering the soil as a heterogeneous bioreactor, a method is developed that permits a quantitative evaluation of O-2 and CO2 levels in the soil atmosphere. Mathematical modeling allowed us to quantitate the rate at which soil 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 recently 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 subjected to agriculture. We conclude that qO(2) reflects more accurately than qCO(2) the contribution of microbial activity to the rate of gas exchanges in soil. Results are discussed in terms of soil biogeochemical processes.