Choice of emission factors

Annual average nitrogen excretion rates, Nex(T)

Tier 1

Annual nitrogen excretion rates should be determined for each livestock category defined by the livestock population characterisation. Country-specific rates may either be taken directly from documents or reports such as agricultural industry and scientific literature, or derived from information on animal nitrogen intake and retention (as explained below). In some situations, it may be appropriate to use excretion rates developed by other countries that have livestock with similar characteristics.

If country-specific data cannot be collected or derived, or appropriate data are not available from another country, the IPCC default nitrogen excretion rates presented in Table 10.19 can be used. These rates are presented in units of nitrogen excreted per 1000 kg of animal per day. These rates can be applied to livestock sub-categories of varying ages and growth stages using a typical average animal mass (TAM) for that population sub-category, as shown in Equation 10.30.

Where:

Nex(T) = annual N excretion for livestock category T, kg N animal-1 yr-1

Nrate(T) = default N excretion rate, kg N (1000 kg animal mass)-1 day-1 (see Table 10.19)

TAM(T) = typical animal mass for livestock category T, kg animal-1

Default TAM values are provided in Tables 10A-4 to 10A-9 in Annex 10A.2. However, it is preferable to collect country-specific TAM values due to the sensitivity of nitrogen excretion rates to different weight categories. For example, market swine may vary from nursery pigs weighing less than 30 kilograms to finished pigs that weigh over 90 kilograms. By constructing animal population groups that reflect the various growth stages of market pigs, countries will be better able to estimate the total nitrogen excreted by their swine population.

When estimating the Nex(T) for animals whose manure is classified in the manure management system burned for fuel (Table 10.21, Default emission factors for direct N2O emissions from Manure Management), it should be kept in mind that the dung is burned and the urine stays in the field. As a rule of thumb, 50% of the nitrogen excreted is in the dung and 50% is in the urine. If the burned dung is used as fuel, then emissions are reported under the IPCC category Fuel Combustion (Volume 2: Energy), whereas if the dung is burned without energy recovery the emissions should be reported under the IPCC category Waste Incineration (Volume 5: Waste).

Tier 2

The annual amount of N excreted by each livestock species/category depends on the total annual N intake and total annual N retention of the animal. Therefore, N excretion rates can be derived from N intake and N retention data. Annual N intake (i.e., the amount of N consumed by the animal annually) depends on the annual amount of feed digested by the animal, and the protein content of that feed. Total feed intake depends on the production level of the animal (e.g., growth rate, milk production, draft power). Annual N retention (i.e., the fraction of N intake that is retained by the animal for the production of meat, milk, or wool) is a measure of the animal's efficiency of production of animal protein from feed protein. Nitrogen intake and retention data for specific livestock species/categories may be available from national statistics or from animal nutrition specialists. Nitrogen intake can also be calculated from data on feed and crude protein intake developed in Section 10.2. Default N retention values are provided in Table 10.20, Default values for the fraction of nitrogen in feed taken in by animals that is retained by the different animal species/categories. Rates of annual N excretion for each livestock species/category (Nex(T)) are derived as follows:

Where:

NeX(T) = annual N excretion rates, kg N animal-1 yr-1

Nintake(T) = the annual N intake per head of animal of species/category T , kg N animal-1 yr-1 Nretention(T) = fraction of annual N intake that is retained by animal of species/category T, dimensionless

Example of Tier 2 method for estimating nitrogen excretion for cattle

Nitrogen excretion may be calculated based on the same dietary assumptions used in modelling enteric fermentation emissions (see Section 10.2). The amount of nitrogen excreted by cattle can be estimated as the difference between the total nitrogen taken in by the animal and the total nitrogen retained for growth and milk production. Equations 10.32 and 10.33 can be used to calculate the variables for nitrogen intake and nitrogen retained for use in Equation 10.31. The total nitrogen intake rate is derived as follows:

Where:

Nintake(T) = daily N consumed per animal of category T, kg N animal-1 day-1

GE = gross energy intake of the animal, in enteric model, based on digestible energy, milk production, pregnancy, current weight, mature weight, rate of weight gain, and IPCC constants, MJ animal-1 day-1

18.45 = conversion factor for dietary GE per kg of dry matter, MJ kg-1. This value is relatively constant across a wide range of forage and grain-based feeds commonly consumed by livestock.

CP% = percent crude protein in diet, input

6.25 = conversion from kg of dietary protein to kg of dietary N, kg feed protein (kg N)-1

Chapter 10: Emissions from Livestock and Manure Management

Table 10.19

Default values for nitrogen excretion rate a (kg N (1000 kg animal mass)-1 day-1)

Category of animal

Region

North America

Western Europe

Eastern Europe

Oceania

Latin America

Africa

Middle East

Asia

Dairy Cattle

0.44

0.48

0.35

0.44

0.48

0.60

0.70

0.47

Other Cattle

0.31

0.33

0.35

0.50

0.36

0.63

0.79

0.34

Swineb

0.50

0.68

0.74

0.73

1.64

1.64

1.64

0.50

Market

0.42

0.51

0.55

0.53

1.57

1.57

1.57

0.42

Breeding

0.24

0.42

0.46

0.46

0.55

0.55

0.55

0.24

Poultry

0.83

0.83

0.82

0.82

0.82

0.82

0.82

0.82

Hens >/= 1 yr

0.83

0.96

0.82

0.82

0.82

0.82

0.82

0.82

Pullets

0.62

0.55

0.60

0.60

0.60

0.60

0.60

0.60

Other Chickens

0.83

0.83

0.82

0.82

0.82

0.82

0.82

0.82

Broilers

1.10

1.10

1.10

1.10

1.10

1.10

1.10

1.10

Turkeys

0.74

0.74

0.74

0.74

0.74

0.74

0.74

0.74

Ducks

0.83

0.83

0.83

0.83

0.83

0.83

0.83

0.83

Sheep

0.42

0.85

0.90

1.13

1.17

1.17

1.17

1.17

Goats

0.45

1.28

1.28

1.42

1.37

1.37

1.37

1.37

Horses (and mules, asses)

0.30

0.26

0.30

0.30

0.46

0.46

0.46

0.46

Camelsc

0.38

0.38

0.38

0.38

0.46

0.46

0.46

0.46

Buffaloc

0.32

0.32

0.32

0.32

0.32

0.32

0.32

0.32

Mink and Polecat (kg N head-1 yr-

!)d

4.59

4.59

4.59

4.59

4.59

4.59

4.59

4.59

Rabbits (kg N head-1 yr-1)

8.10

8.10

8.10

8.10

8.10

8.10

8.10

8.10

Fox and Racoon (kg N head-1 yr-1)d

12.09

12.09

12.09

12.09

12.09

12.09

12.09

12.09

The uncertainty in these estimates is +50%.

a Summarized from 1996 IPCC Guidelines, 1997; European Environmental Agency, 2002; USA EPA National NH3 Inventory Draft Report, 2004; and data of GHG inventories of Annex I Parties submitted to the Secretariat UNFCCC in 2004.

Nitrogen excretion for swine are based on an estimated country population of 90% market swine and 10% breeding swine. c Modified from European Environmental Agency, 2002. dData of Hutchings et al, 2001.

Table 10.20

Default values for the fraction of nitrogen in feed intake of livestock that is retained by

THE DIFFERENT LIVESTOCK SPECIES/CATEGORIES (FRACTION N-INTAKE RETAINED BY THE ANIMAL)

(kg N retained/animal/year) (kg N intake/animal/year)-1

Dairy Cows

0.20

Other Cattle

0.07

Buffalo

0.07

Sheep

0.10

Goats

0.10

Camels

0.07

Swine

0.30

Horses

0.07

Poultry

0.30

The uncertainty in these estimates is +50%.

Source: Judgement of IPCC Expert Group (see Co-chairs, Editors and Experts; N2O emissions from Manure Management).

The total nitrogen retained is derived as follows:

EQUATION 10.33 N RETAINED RATES FOR CATTLE

retention(T)

Milk

Milk PR% 100

6.38

1000 6.25

Where:

Nretention(T) = daily N retained per animal of category T, kg N animal-1 day-1 Milk = milk production, kg animal-1 day-1 (applicable to dairy cows only)

Milk PR% = percent of protein in milk, calculated as [1.9 + 0.4 • %Fat], where %Fat is an input, assumed to be 4% (applicable to dairy cows only)

6.38 = conversion from milk protein to milk N, kg Protein (kg N)-1

WG = weight gain, input for each livestock category, kg day-1

268 and 7.03 = constants from Equation 3-8 in NRC (1996)

NEg = net energy for growth, calculated in livestock characterisation, based on current weight, mature weight, rate of weight gain, and IPCC constants, MJ day-1

1000 = conversion from grams per kilogram, g kg-1

6.25 = conversion from kg dietary protein to kg dietary N, kg Protein (kg N)-1

Annual nitrogen excretion data are also used for the calculation of direct and indirect N2O emissions from managed soils (see Chapter 11, Section 11.2, N2O emissions from managed soils). The same rates of N excretion, and methods of derivation, that are used to estimate N2O emissions from Manure Management should be used to estimate N2O emissions from managed soils.

Emission factors for direct N2O emissions from Manure Management

The best estimate will be obtained using country-specific emission factors that have been fully documented in peer reviewed publications. It is good practice to use country-specific emission factors that reflect the actual duration of storage and type of treatment of animal manure in each management system that is used. Good practice in the derivation of country-specific emission factors involves the measurement of emissions (per unit of manure N) from different management systems, taking into account variability in duration of storage and types of treatment. When defining types of treatment, conditions such as aeration and temperature should be taken into account. If inventory agencies use country-specific emission factors, they are encouraged to provide justification for these values via peer-reviewed documentation.

If appropriate country-specific emission factors are unavailable, inventory agencies are encouraged to use the default emission factors presented in Table 10.21, Default emission factors for direct N2O emissions from Manure Management. This table contains default emission factors by manure management system. Note that emissions from liquid/slurry systems without a natural crust cover, anaerobic lagoons, and anaerobic digesters are considered negligible based on the absence of oxidized forms of nitrogen entering these systems combined with the low potential for nitrification and denitrification to occur in the system.

Emission factors for indirect N2O emissions from Manure Management

In order to estimate indirect N2O emissions from Manure Management, two fractions of nitrogen losses (due to volatilization and leaching/runoff), and two indirect N2O emissions factors associated with these losses (EF4 and EF5) are needed. Default values for volatilization N losses are presented in the Table 10.22. Values represent average rates for N loss in the forms of NH3 and NOx, with most of the loss in the form of NH3. Ranges reflect values that appear in the literature. The values represent conditions without any significant nitrogen control measures in place. Countries are encouraged to develop country-specific values, particularly related to ammonia losses where component emissions may be well characterized as part of larger air quality assessments and where emissions may be affected by nitrogen reduction strategies. For example, detailed methodologies for estimating NH3 and other nitrogen losses using mass balance/mass flow procedures are described in the EMEP/CORINAIR Atmospheric Inventory Guidebook, Chapter 1009 (European Environmental Agency, 2002).

The fraction of manure nitrogen that leaches from manure management systems (FracleachMS) is highly uncertain and should be developed as a country-specific value applied in Tier 2 method.

Default values for EF4 (N volatilisation and re-deposition) and EF5 (N leaching/runoff) are given in Chapter 11, Table 11.3 (Default emission, volatilisation and leaching factors for indirect soil N2O emissions).

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment