Garden with Insight v1.0 Help: Nitrogen  Nitrification
Nitrification, the conversion of ammonia N to nitrate N, is estimated using a combination of the methods
of Reddy et al. (1979) and Godwin et al. (1984). The approach is based on the firstorder kinetic rate
equation of Reddy et al. (1979)
RNV = WNH3 (1.0  exp(AKN  AKV)) (Equation 185)
where RNV is the combined nitrification and volatilization in kg/ha, WNH3 is the weight of NH3 in
kg/ha, AKN is the nitrification regulator, and AKV is the volatilization regulator for soil layer l.
The nitrification regulator is a function of temperature, soil water content, and soil pH as expressed in the
equation [Equation 186] where TF is the temperature factor.
Equation 186
AKN = TF * SWF * PHF
Code:
same
Variables:
AKN = NitrifRegulatorForLayer
TF = nitrifAndVolatilTempFactor
SWF = nitrifSoilWaterFactor
PHF = nitrifPHFactor
The temperature factor is estimated with the equation [Equation 187] where T(l) is the temperature of soil
layer l in degrees C.
Equation 187
TF = 0.41 * (T  5.0) / 10.0
Code:
same
Variables:
TF = NitrifAndVolatilTempFactorForLayer
T = temperature_degC
The soil water factor, SWF, is computed with the equations [Equation 188], [Equation 189] and [Equation
190] where SW is the soil water content, WP is the wilting point soil water content, FC is the field
capacity soil water content, and SW25 is the water content at WP+0.25(FCWP) all in mm for soil layer l.
Equation 188, 189, 190
SW25 = WP + 0.25 * (FC  WP)
if SW < SW25, SWF = (SW  WP) / (SW25  WP)
if SW25 < SW < FC, SWF = 1.0
if SW > FC, SWF = max(0.0, 1.0  (SW  FC) / (PO  FC))
Code:
same, except code adds another case: if SW < WP, SWF = 0
Variables:
SWF = NitrifSoilWaterFactorForLayer
SW = waterContent_mm
WP = wiltingPoint_mm
FC = fieldCapacity_mm
SW25 = threshold_mm
PO = porosity_mm
The soil pH factor PHF is computed with the equations [Equation 191], [Equation 192] and [Equation
193] where PH is the soil pH for soil layer l.
Equation 191, 192, 193
if PH < 7, PHF = 0.307 * PH  1.269
if 7 < PH < 7.4, PHF = 1.0
if PH > 7.4, PHF = 5.367  0.599 * PH
Code:
same
Variables:
PHF = NitrifPHFactorForLayer
PH = soilpH
