10. N Losses from Soil

Part of the N applied to the soil is lost in forms of gaseous emissions, including NH3, N2O, and NOx, as well as surface runoff and leaching. The following table summarizes the emissions from different sources that are calculated in the Miterra models.

Mineral Fertilisers Manure Application Grazing Excretion Crop Residues

NH3

✅

✅

✅

N2O

✅

✅

✅

✅

NOx

✅

✅

✅

Surface Runoff

✅

✅

✅

Leaching [1]

✅

10.1. N application to soil

N losses from soil are calculated on the basis of the amount of N applied to the soil. Estimation of N applications are described in 7. Fertilization.

Equation 10.1

where:

is the total N or TAN content applied to the soil from different sources (kg N ha–1).

is the rate N deposition from excretions during the grazing period (kg N ha–1). See 7.1. Distribution of grazing excretions and Equation 7.1.

is the application rate of manure N to the soil (kg N ha–1). See 7.2. Distribution of animal manure and Equation 7.9.

is the application rate of mineral N fertilisers to the soil (kg N ha–1). See 7.4. Distribution of mineral N fertilisers and Equation 7.15.

is the total N or TAN content by the end of the storage period (kg N ha–1). See Equation 4.11.

10.2. NH3 volatilization

Mineral fertilisers and solid manure

For solid manure applied to the field or deposited during grazing, NH3-N volatilization is calculated as a fraction of the TAN applied. For mineral N fertilisers, NH3-N emissions depends on total N applied and soil pH.

Equation 10.2

For mineral N fertilisers:

For manure:

where:

is the amount of NH3-N emission after N application to the soil (kg N ha–1).

is the amount of total N applied to the soil in mineral N fertilisers, or TAN in manure or grazing excretion (kg N ha–1). See Equation 10.1.

is the specific NH3 emission factor which differs depending on the TAN source.

Mineral N fertilisers
depends on the type of the fertiliser, and the soil pH.

Mineral N Fertiliser Type Miterra Code [1] Soil pH ≤ 7 Soil pH > 7

Anhydrous ammonia

N_AA

0.02

0.02

Ammonium nitrate

N_AN

0.024

0.052

Ammonium phosphate

DAP, MAP

0.084

0.187

Ammonium sulfate

N_AS

0.084

0.187

Calcium ammonium nitrate

N_CAN

0.024

0.052

NK mixtures

KN, N_SN, Other_NK

0.024

0.052

NPK mixtures

NPK

0.084

0.187

NP mixtures

Other_NP

0.084

0.187

N solutions

UAN

0.087

0.161

Other straight N compounds

F_NEC, N_ONF

0.024

0.187

Urea

N_Urea

0.195

0.206

[1] Corresponding chemical fertiliser codes used in Miterra (see Chemical fertiliser codes in Appendix).
Reproduced from Table 3-2 of Chapter 3.D of the EMEP Guidebook 2023.

Solid manure
is given in Table 4.1 (Eapplication for manure application, and Egrazing for grazing excretion).

Liquid slurry

For liquid slurry, NH3-N emissions are estimated using the ALFAM2 model, which adopts a more dynamic approach taking into account slurry composition, climate, and application method.

10.3. N2O emissions

N2O emissions are calculated using EFs following the 2019 IPCC Guidelines.

Equation 10.3

where:

is the amount of N2O-N emission after N application to the soil (kg N ha–1).

is the total N content in mineral N fertilisers, manures, grazing excretion, or crop residues applied to the soil (kg N ha–1). See Equation 10.1.

is the N2O emission factor which differs depending on climate zones and N sources.

N Source Cool Moist Cool Dry Warm Moist Warm Dry

Mineral Fertiliser

0.016

0.005

0.016

0.005

Manure

0.006

0.005

0.006

0.005

Crop Residues

0.006

0.005

0.006

0.005

Grazing (Cattle, Poultry & Pigs)

0.006

0.002

0.006

0.002

Grazing (Sheep, Horses & Other)

0.003

0.003

0.003

0.003

Volatilization

0.014

0.005

0.014

0.005

The climate zones are determined based on annual average temperature (T; °C), annual total precipitation (P; mm) and annual total evapotranspiration (E; mm).

Climate Zone Criteria

Cool Moist

Cool Dry

Warm Moist

Warm Dry

10.4. NOx emissions

The emission factor for NOx is linked to annual precipitation amount.

Equation 10.4

where:

is the amount of NOx-N emission after N application to the soil (kg N ha–1).

is the total N content in mineral N fertilisers, manures, or grazing excretion (kg N ha–1). See Equation 10.1.

is the NOx emission factor which differs depending on the annual precipitation of the region.

Precipitation (mm)

< 400

[400, 600)

[600, 800)

[800, 1000)

[1000, 1500)

≥ 1500

0.0019

0.0059

0.0071

0.0048

0.0018

0.0024

10.5. Surface runoff of N

N loss via surface runoff is calculated using a runoff fraction:

Equation 10.5

where:

is the total N content lost via surface runoff following N application to the soil (kg N ha–1).

is the total N content in mineral N fertilisers, manures, or grazing excretion (kg N ha–1). See Equation 10.1.

is the runoff fraction of precipitation surplus (unitless). See Equation 5.1.

10.6. N surplus

Three types of N surpluses are defined in Miterra:

Equation 10.6

Gross N surplus
Nsurplus, gross is the difference between gross N input and crop N removal (both by harvest and residue removal) at farm level.

Soil N surplus
Nsurplus, soil is the difference between soil N addition and crop N removal at field level. Soil N surplus is an indicator for the potential of N losses to the environment.

Corrected soil N surplus
Nsurplus, corrected is the difference between soil N addition and soil N losses, including gaseous emissions, surface runoff, and crop removal. Corrected soil N surplus reflects the potential for N leaching and denitrification.

where:

is the total N in livestock excretion. See Equation 3.1.

is the total N content in mineral fertilisers applied to the soil. See Equation 7.15.

is the total N content in compost applied to the soil. See 8.2. Nutrient content in compost.

is the total N content in sludge applied to the soil. See 8.3. Nutrient content in sludge.

is the total atmospheric NH3 and NOx depositions in the region.

is the biologically fixated N. See 6.6. Biological N fixation.

is the total N input to soil from external sources. See Equation 9.1.

is the total N content removed by harvest and residue removal. See 6.4. Residue removal & incorporation.

is the total N content lost via atmospheric emissions. See Equation 10.2, Equation 10.3, and Equation 10.4.

is the total N content lost via surface runoff. See Equation 10.5.

All terms are expressed in kg N ha–1.

10.7. N leaching

The Miterra models assume that there is no change in the soil mineral N pool, and that all N applied to the soil which is not lost at soil surface, nor taken up by the crop, are either leached below root zone, or lost to the atmosphere via denitrification.

N leaching may be determined in two parallel approaches:

Method 1: Conventional Miterra Approach

Leaching is a fraction of the corrected soil total N surplus (i.e., the organic and mineral N fractions are lumped) as described in Equation 10.6.

Method 2: The RothCN Approach

The RothCN model calculates changes in soil mineral N pool as the balance of mineralization and immobilization during soil organic matter decomposition. Leaching is then estimated as a fraction of corrected soil mineral N surplus (See 15B.2. Emissions and balances).

Equation 10.7

where:

is the total N content lost via leaching below the root zone following N application to the soil (kg N ha–1).

is the corrected soil N surplus (kg N ha–1). See Equation 10.6.

is the fraction of precipitation surplus leached below the root zone (unitless). See Equation 5.4.

The N that has leached below root zones are further partitioned to leaching to deep groundwater, and interflow that end up in large surface waters, which are determined by a ground flow fraction.

Equation 10.8

where:

is the leached N content partitioned to deep groundwater, or surface interflow (kg N ha–1).

is the total N content leached (kg N ha–1). See Equation 10.7.

is the fraction of water flux to deep groundwater (unitless), which is a region-specific coefficient based on the modelling by Keuskamp et al. (2012).

The part of Nsurplus, corrected that is not leached, is denitrified.

Equation 10.9

where:

is the total N content for denitrification (kg N ha–1).

is the corrected soil N surplus (kg N ha–1). See Equation 10.6.

is the total N content leached (kg N ha–1). See Equation 10.7.
Due to the nature of approximate estimation in Miterra, the calculated Nsurplus, corrected may be < 0. In that case, Nsurplus, corrected, leaching, and denitrification should all be set to 0 to avoid negative values.