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#### Garden with Insight v1.0 Help: Nitrogen - Volatilization

Volatilization, the loss of ammonia to the atmosphere, is estimated simulataneously with nitrification. Volatilization of surface-applied 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:
same
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:
same
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:
same
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:
same
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:
same
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(l-1)) / 2
Code:
same
Variables:
ZZ = DepthToMiddleOfSoilLayer_mm
Z(l) = depth_m
Z(l-1) = 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:
same
Variables:
AKN = nitrifRegulatorForLayer

Equation 201

RVOL = 1.0 - exp(-AKV)
Code:
same
Variables:
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