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Dynamic Oxygen and Carbon Dioxide Exchange between Soil and Atmosphere: II. Model Simulations

Soil and Water Science Dep., Univ. of Florida, Gainesville, FL 32611

L. Boersma^*

Dep. of Crop and Soil Science, Oregon State Univ., Corvallis, OR 97331

*Corresponding author.

ABSTRACT

An important general objective for modeling gaseous transport through unsaturated soils is to provide better understanding of gas exchange between the terrestrial ecosystem and the atmosphere. A more specific objective is the evaluation of problems of soil aeration. We present sensitivity analyses of a mathematical model developed for the dynamic exchange of O₂ and CO₂ between soil and atmosphere. We also present simulations to evaluate changes in concentrations during cycles of infiltration, evaporation, and redistribution during which simultaneous transport of water, heat, O₂, and CO₂ was involved. Simulation was also used to evaluate possible effects of O₂ and CO₂ concentrations on the rate of root growth; effects of a compacted layer on the simultaneous transport of water, O₂, and CO₂; effect of the presence of a crop canopy on concentrations of O₂ and CO₂ in the soil; and an evaluation of possible nonideal behavior of CO₂ molecules in the gas phase of the soil. Results emphasize the important effects of rainfall, evaporation, and root respiration on O₂ and CO₂ concentrations in the soil. Simulations show that root growth below a compacted soil layer may be restricted by low O₂ concentrations resulting from limited diffusion through the compacted layer. The presence of a crop canopy has a decisive effect on concentrations of O₂ and CO₂ at the soil surface, thereby affecting the concentrations of those gases in the root zone.

Contribution from the Oregon Agric. Exp. Stn.

Received for publication April 12, 1991.