Knowledge of CO2 emission from the soil is important because it helps us to evaluate its contribution to the greenhouse or global warming effect. In this study we compare experimentally determined CO2 fluxes exiting the soil surface with the results of an existing deterministic model (Hydrus 1-D) and a simplified model. The latter is based on reduction functions related to soil temperature, soil water content, and time of year as the independent variables. With increasing values of an independent variable, each reduction function consists of 3 parts, viz., the first part with increasing values, the second part consisting of a plateau with a constant value, and the third part with decreasing values. CO2 fluxes were measured throughout the year 2004 at 26 locations on a field grown with corn, half of which had been subjected to standard tillage (15 measurement locations) and the other half to minimum tillage (11 measurement locations). Furrow irrigation was applied on a regular basis. It was shown that the reduction functions could reasonably well predict the CO2 fluxes across the soil surface. Due to the relative large amount of noise in the measured CO2 flux values, they were averaged by tillage treatment. Average measured values and average predicted values resulted in a regression coefficient of 0.76 for both tillage treatments. The deterministic model is a dynamic model and includes simultaneous heat, water and gas flow.