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]

✅

NH3 volatilization

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 10.1

For mineral N fertilisers:

For manure:

where:

is the amount of total N applied to the soil in mineral N fertilisers.

is the amount of TAN applied to the soil in manures or grazing excretion.

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

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

Mineral N Fertiliser Type Soil pH ≤ 7 Soil pH > 7

Anhydrous ammonia (AH)

0.02

0.02

Ammonium nitrate (AN)

0.024

0.052

Ammonium phosphate

0.084

0.187

Ammonium sulfate (AS)

0.084

0.187

Calcium ammonium nitrate (CAN)

0.024

0.052

NK mixtures

0.024

0.052

NPK mixtures

0.084

0.187

NP mixtures

0.084

0.187

N solutions

0.087

0.161

Other straight N compounds

0.024

0.187

Urea

0.195

0.206

️ Reproduced from Table 3-2 of Chapter 3.D of the EMEP Guidebook 2023.

Solid manure
EFs are 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.

N2O emissions

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

Equation 10.2

where:

is the total N content in mineral N fertilisers, manures, grazing excretion, or crop residues.

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 Residsue

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), annual total precipitation (P) and annual total evapotranspiration (E).

Climate Zone Criteria

Cool Moist

Cool Dry

Warm Moist

Warm Dry

NOx emissions

Emission factor for NOx is linked to annual precipitation amount.

Equation 10.3

where:

is the total N content in mineral N fertilisers, manures, or grazing excretion.

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

Surface runoff of N

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

Equation 10.4

where:

is the total N content in mineral N fertilisers, manures, or grazing excretion.

is the runoff fraction of precipitation surplus, which is calculated in Surface runoff.

N surplus

Three types of N surpluses are defined in Miterra:

Gross N surplus

is the difference between gross N input and crop N removal (both by harvest and residue removal) at farm level:

Equation 10.5

where:

is the total N in livestock excretion produced at farm level or in the region (see N content in livestock excretion).

is the total N removed by harvest and residue removal at farm level or in the region (see Residue removal & incorporation).
Soil N surplus

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.

Equation 10.6
Corrected soil N surplus

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

Equation 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 denitirfication.

N leaching may be determined in two parallel approaches:

Method 1: Coventional 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 10.7.

Method 2: The RothCN Approach

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

Equation 10.8

where:

is the fraction of precipitation surplus leached below the root zone, which is calculated in Leaching.
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.

The N that has leached below root zones are further partitioned to leaching to groundwater, and interflow that end up in large surface waters, which are determined by a ground flow fraction ( ). The ground flow fraction is a region-specific coefficient based on the modelling by Keuskamp et al. (2012).

Equation 10.9

The part of N(surplus, corrected) that is not leached, is denitrified.

Equation 10.10