4. N Emissions from Manure Management

In this section, N emissions from livestock housing, farmyard, and manure storage are calculated. N emissions during field application of manure, and during grazing period are calculated in 10. N Losses from Soil when they are added to the soil.

Emissions of N are calculated separately for each type of animal, and for both solid and liquid forms, in each MMS. Unless otherwise specified, the units for all N terms are kg N ha^–1 yr^–1. The following table summarises the pathways for N emissions and losses calculated in this section.

	Housing	Yard	Storage
NH₃	✅	✅	✅
N₂O			✅
NO_x	✅		✅
N₂			✅
Loss to water ^[1]			✅

Housing

Yard

Storage

NH₃

✅

N₂O

✅

NO_x

✅

N₂

✅

Loss to water ^[1]

✅

[1] Includes combined runoff and leaching during manure storage.

NH₃-N emissions are calculated on the basis of total ammoniacal N (TAN), following the approach by the EMEP/EEA air pollutant emission inventory guidebook 2023 (hereafter “EMEP Guidebook 2023”), with some simplification due to limitation on data availability. All the other gaseous N emissions are calculated based on total N.

The amounts of total N in solid and liquid forms of each type of animal manure in each stage are determined following the steps as described in N content in livestock excretion.

	Solid	Liquid
Housing	N_{housing, soli}	N_{housing, liquid}
Farmyard	N_{yard, solid}	N_{yard, liquid}
Grazing	N_{grazing, solid}	N_{grazing, liquid}

Solid

Liquid

Housing

N_{housing, soli}

N_{housing, liquid}

Farmyard

N_{yard, solid}

N_{yard, liquid}

Grazing

N_{grazing, solid}

N_{grazing, liquid}

Next, the amounts of TAN deposited during housing, yard, and grazing period, are calculated by multiplying N content with TAN fraction:

Equation 4.1

where:

is the proportion of TAN in total N (see Table 4.1).

Table 4.1: Emission factors and associated parameters for the calculation of NH₃-N emissions from manure management.
Livestock Manure	f_TAN	E_housing	E_yard	E_storage	E_application	E_grazing
Dairy cattle	0.6	0.08	0.30	0.32	0.68	0.14
Non-dairy cattle	0.6	0.08	0.53	0.32	0.68	0.14
Finishing pigs	0.7	0.23	0.53	0.29	0.45
Sows & piglets	0.7	0.24		0.29	0.45
Sheep	0.5	0.22	0.75	0.32	0.90	0.09
Goats	0.5	0.22	0.75	0.28	0.90	0.09
Horses	0.6	0.22		0.35	0.90	0.35
Buffalo	0.5	0.20		0.17	0.55	0.14
Laying hens	0.7	0.20		0.08	0.45
Broilers	0.7	0.21		0.30	0.38
Other poultry	0.7	0.39		0.21	0.51
Other animals	0.6	0.27		0.09

️ Reproduced from Table 3-9 of Chapter 3.B of the EMEP Guidebook 2023.

N Emissions from livestock housing

Emissions of NH₃-N and NO_x-N are calculated during livestock housing.

The NH₃-N emissions during housing are calculated by multiplying TAN with corresponding emission factors:

Equation 4.2

where:

	is the NH₃-N emission factor as specified in Table 4.1.
	is the fraction of emission reduction by applying NH₃ abatement technique i during housing phase.
	is the fraction of farms that adopted the NH₃ abatement technique in the region.
	is the set of NH₃ abatement techniques applied in the region (i ∈ n).

The NO_x-N emissions during housing are calculated similarly to NH₃-N, but by multiplying total N with corresponding emission factors:

Equation 4.3

where:

is the NO_x-N emission factor with a default value of 0.003 for all animal manure in all countries.

The next step is only relevant to solid manure deposited in livestock houses. It acccounts for the addition of N in animal bedding in litter-based housing systems, and the consequent immobilisation of TAN in that bedding. Total N and TAN in solid manure are then removed from livestock housing (denoted by ex_housing subscript), and passed to storage system, subtracting the gaseous N emissions.

Equation 4.4

where:

	is the mass of bedding straw added (kg fresh weight yr^–1).
	is the immobilization coefficient with a default value of 0.0067 kg N kg^–1 straw ( Kirchmann & Witter, 1989; and Webb & Misselbrook, 2004).
	is the mass of N in that bedding straw (kg N yr^–1).

Default values for length of housing period, annual straw use in litter-based manure management systems, and the N content of straw are given below. If the actual housing period deviates from the values in the table, the amounts of straw and straw N added should be adjusted proportionally to the actual housing days.

Livestock	Housing Period (day)	Straw (kg head^–1 yr^–1)	N Added in Straw (kg N head^–1 yr^–1)
Dairy cattle	180	1500	6.0
Non-dairy cattle	180	500	2.0
Pigs	365	200	0.8
Sheep & goats	30	20	0.08
Horses	180	500	2.0

️️ Reproduced from Table 3-7 of Chapter 3.B of the EMEP Guidebook 2023.

N emissions from farmyard

Emissions of NH₃-N are calculated for farmyard.

Equation 4.5

where:

is the NH₃-N emission factor as specified in Table 4.1.

N losses from manure storage

Emissions of NH₃-N, N₂O-N, NO_x-N, N₂-N, and NO₃^–-N losses to water are calculated for manure storage.

In the first step, the amounts of total N and TAN that are passed to storage system are calculated. It is assumed that all yard manure (both solid and liquid forms) are collected into the slurry storage system.

This step simplifies the method in EMEP Guidebook by assuming that all manure are stored before application. Manures applied to fields directly from livestock housing, and manures (mainly slurries) used as feedstocks for digestion, are not considered due to lack of reliable estimation.

Equation 4.6

For liquid slurry:

For solid manure:

The NH₃-N emissions from storage are calculated by applying emission factors on TAN.

Equation 4.7

where:

is the NH₃-N emission factor as specified in Table 4.1.

All other gaseous N emissions are calculated by applying emission factors on total N.

Equation 4.8

Part of the N may also be lost to water as NO₃^– during storage. This can take place via seepage through the bottom of the storage tank, or via overflow during precipitation.

Equation 4.9

where:

is the emission factor of leaching during storage (kg N per kg excreted N per year), which is specific to the type of manure and storage system.

Manure Type

Storage System

Concrete Floor

Cover

Liquid slurry

❌

0.2

❌

✅

0.15

✅

0.0

Solid manure

❌

0.1

❌

✅

0.02

✅

❌

0.05 ^[1]

✅

0.0

[1] Assuming that some manure may be washed from the concrete floor to the surrounding soil.

Finally, the amounts of total N and TAN remaining after storage (denoted by ex_storage subscript) are calculated. Total N and TAN in solid and liquid forms may be combined at this step.

Equation 4.10

where i ∈ {solid, liquid}, and j ∈ {NH₃, N₂O, NO_x, N₂}.

Total N and TAN remaining after storage (N_{ex_storage} and TAN_{ex_storage}) is applicable to the fields as organic fertilisers. The distribution of applicable manure N to different crops are described in 7. Fertilization.