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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.

Handout (.pdf format, 211.0 kb)