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 first-order 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(FC-WP) 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