THE FLORIDA STATE UNIVERSITY ARTS AND SCIENCES ...

Da is the denitrification rate (mg N kg −1 soil d −1 ) and Dp is the potential denitrification
(mg N kg −1 soil d −1 ). The denitrification potential can be either a long term denitrification
potential or a Denitrifying Enzyme Activity (DEA). fN is a nitrate dimensionless
function, where N is the actual nitrate soil content (mg N kg −1 soil) and K is the nitrate
soil content (mg N kg −1 soil) when fN =0.5. fS is a dimensionless function of water
saturation, where S is the WFPS, St the WFPS threshold below which denitrification does
not occur and Sm the maximal WFPS (in our case Sm = 1). fT is a dimensionless
function of the soil temperature T (ºC), Tr is the reference temperature when the potential
denitrification Dp was determined, and Q10 is the increase factor for a temperature
increase of 10ºC. This function has a specific from in NEMIS, where two different Q10
are used for two ranges of temperature:
ref
T −Tr
10
10
fT = fT * Q
----
20
Equation 1.9
The disadvantage of this model is that it requires a potential denitrification rate. As the
database was constructed using actual denitrification rates it was not possible to use this
method. In addition it would have defeated the purpose of using existing data to create a
denitrification model. The model has been tested by several authors and can perfrom
quite well when calibrated for a specific site (Heinen, 2006b) but the model does not
perfrom as well when applied over a range of different soil types with the same parameter
set (Oehler 2010).
1.5.3. Colbourn (1992)
Colbourn (1992) developed a simplified model based on the moisture content,
temperature and nitrate available. The model was derived empirically based on published
data. The drawback of the model is that it does not take account of the effect of carbon on
the denitrification rate.
R dn
= exp ( 0.
71+
0.
5N
) * exp (0.1 S + 0.1T
- 8.3)
---- Equation 1.10