Note: This page is no longer being maintained and is kept for archival purposes only.
For current information see our main page.
Garden with Insight Kurtz-Fernhout Software
Developers of custom software and educational simulations.
Home ... News ... Products ... Download ... Order ... Support ... Consulting ... Company
Garden with Insight
Product area
Help System
Contents
Quick start
Tutorial
How-to
Models

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:
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

Home ... News ... Products ... Download ... Order ... Support ... Consulting ... Company
Updated: March 10, 1999. Questions/comments on site to webmaster@kurtz-fernhout.com.
Copyright © 1998, 1999 Paul D. Fernhout & Cynthia F. Kurtz.