Garden with Insight v1.0 Help: Nitrogen  Volatilization
Volatilization, the loss of ammonia to the atmosphere, is estimated simulataneously with nitrification.
Volatilization of surfaceapplied ammonia is estimated as a function of temperature and wind speed using
the equation [Equation 194] where AKV is the volatilization regulator from equation 185 and WNF is the
wind speed factor for surface application (soil layer 1). (What this means is that a different set of
equations is used for the first soil layer than for the other soil layers.)
Equation 194
AKV = TF * WNF
Code:
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Variables:
AKV = VolatilRegulatorForSurfaceLayer
TF = nitrifAndVolatilTempFactor
WNF = volatilWindSpeedFactorForSurface
The wind speed factor for surface volatilization is estimated with this equation [Equation 195] where V is
the mean wind speed in m/sec for the day.
Equation 195
WNF = 0.335 + 0.16 * ln(V)
Code:
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Variables:
WNF = VolatilWindSpeedFactorForSurface
V = meanWindSpeedForDay_mPsec
Depth of ammonia within the soil, cation exchange capacity of the soil, and soil temperature are used in
estimating below surface volatilization [Equation 196] where CECF is the cation exchange capacity
factor.
Equation 196
AKV = TF * CECF * DPF
Code:
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Variables:
AKV = VolatilRegulatorForNonSurfaceLayer
TF = nitrifAndVolatilTempFactor
CECF = volatilCationExchangeCapFactor
DPF = volatilDepthFactor
The cation exchange capacity factor, CECF, is estimated with the equation [Equation 197] where CEC is
the cation exchange capacity for soil layer l.
Equation 197
CECF = 1.0  0.038 * CEC, CECF >= 0
Code:
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Variables:
CECF = VolatilCationExchangeCapFactorForLayer
CEC = cationExchangeCapacity_cmolPkg
The depth factor, DPF, is computed with the equation [Equation 198] where ZZ is the depth to the middle
of soil layer l in mm. The parameters in equation 198 are set to give DPF = 0.95 at ZZ = 5 mm and DPF =
0.05 at ZZ = 100 mm.
Equation 198
DPF = 1.0  ZZ / (ZZ + exp(4.706  0.0305 * ZZ))
Code:
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Variables:
DPF = VolatilDepthFactorForLayer
ZZ = depthToMiddleOfSoilLayer_mm
The depth to the middle of the soil layer is computed with [Equation 199] where Z is the depth to the
bottom of layer l in mm.
Equation 199
ZZ = 1000 * (Z(l) + Z(l1)) / 2
Code:
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Variables:
ZZ = DepthToMiddleOfSoilLayer_mm
Z(l) = depth_m
Z(l1) = depthUpperLayer_m
To partition nitrification and volatilization rates appropriately, equation 185 is solved for each process
separately [Equation 200] and [Equation 201] where RNIT and RVOL are the separate estimates of
nitrification and volatilization. However, to satisfy equation 185, equations 200 and 201 must be adjusted.
Thus, the final equations [Equation 202] and [Equation 203].
Equation 200
RNIT = 1.0  exp(AKN)
Code:
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Variables:
RNIT = UnadjNitrifForLayer_kgPha
AKN = nitrifRegulatorForLayer
Equation 201
RVOL = 1.0  exp(AKV)
Code:
same
Variables:
RVOL = UnadjVolatilForLayer_kgPha
AKV = volatilRegulator
Equation 185
RNV = WNH3 * (1.0  exp(AKN  AKV))
Code:
same
Variables:
RNV = CombinedNitrifAndVolatilForLayer_kgPha
WNH3 = ammonia_kgPha
AKN = nitrifRegulator
AKV = volatilRegulator
Equation 202
RNIT* = RNV  RVOL*
Code:
RNIT* = RNV * RNIT / (RVOL + RNIT)
(nitrif and volatil are switched, but it comes to the same thing)
Variables:
RNIT* = NitrificationForLayer_kgPha
RNV = combinedNitrifAndVolatil_kgPha
RNIT = unadjNitrif_kgPha
RVOL = unadjVolatil_kgPha
Equation 203
RVOL* = RNV * RVOL / (RVOL + RNIT)
Code:
RVOL* = RNV  RNIT*
(nitrif and volatil are switched, but it comes to the same thing)
Variables:
RVOL* = VolatilizationForLayer_kgPha
RNV = combinedNitrifAndVolatil_kgPha
RNIT* = nitrification_kgPha
