Agriculture Reference
In-Depth Information
Table 14.4.
Some equations used to predict enteric methane emissions from ruminants.
Source
Equation
Blaxter and Clapperton (1965)
CH
4
(MJ day
−1
) = 5.447 + 0.469 × (energy digestibility at mainte-
nance intake, % of GEI) + multiple of maintenance × (9.930 − 0.21
× (energy digestibility at maintenance intake, % of GEI)/100) × GEI
Ellis
et al
. (2009) (Eq G - Linear)
CH
4
(MJ day
−1
) = −1.01 + 2.76 × NDF (kg day
−1
) + 0.722 × starch
(kg day
−1
)
(Eq H - Linear)
CH
4
(MJ day
−1
) = 2.26 + 5.02 × sugar (kg day
−1
) + 0.0236 × forage (%)
(Eq I - Linear)
CH
4
(MJ day
−1
) = 2.72 + 0.0937 × MEI (MJ day
−1
) + 4.31 × cellulose
(kg day
−1
) − 6.49 × hemicellulose (kg day
−1
) − 7.44 × fat (kg day
−1
)
Jentsch
et al
. (2007)
CH
4
(kJ) = 1.62 × digestible crude protein (g) − 0.38 × digestible
crude fat (g) + 3.78 × digestible crude fibre (g) + 1.49 × digestible
N-free extract (g) + 1142
Mills
et al
. (2003) (Linear 1)
CH
4
(MJ day
−1
) = 5.93 + 1.92 × DMI (kg day
−1
)
(Linear 2)
CH
4
(MJ day
−1
) = 8.25 + 0.07 × MEI (MJ day
−1
)
(Linear 3)
CH
4
(MJ day
−1
) = 7.30 + 13.13 × N (kg day
−1
) + 2.04 × ADF
(kg day
−1
) + 0.33 × starch (kg day
−1
)
(Linear 4)
CH
4
(MJ day
−1
) = 1.06 + 10.27 × dietary forage proportion + 0.87 ×
DMI (kg day
−1
)
Moe and Tyrrell (1979)
CH
4
(MJ day
−1
) = 0.341 + 0.511 × NSC (kg day
−1
) + 1.74 ×
hemicellulose (kg day
−1
) + 2.652 × cellulose (kg day
−1
)
MEI, metabolizable energy intake; EE, ether extract; GEI, gross energy intake; NSC, non-structural carbohydrates
(starch+sugar).
Manure CH
4
Volatile solid production is then multiplied by
the maximum CH
4
producing capacity of the
manure, which varies by animal species and
diet composition, and then by the CH
4
conver-
sion factor (MCF). The MCF is specific to the
manure management storage system and the
average annual temperature of the location.
The MCF ranges from <2% for solid manure
storage systems in temperatures <14°C to
80% for aerobically stored manure in temper-
atures >28°C (such as liquid slurry without
natural crust cover, uncovered anaerobic
lagoons, pit below the animal confinement),
thus temperature and storage facility have a
large impact on the emission.
The CH
4
emission from manure is a function of
the amount of manure produced by the animal
and the portion of the manure that decom-
poses anaerobically. Anaerobic conditions occur
mainly when manure is stored in liquid-based
systems such as lagoons, ponds, tanks or pits.
Conditions tend to be more aerobic when
manure is stacked or piled, or when it is depos-
ited on pastures and rangelands, and thus the
CH
4
emissions are lower in this case. The IPCC
(2006) tier 1 methodology estimates CH
4
emis-
sions from manure by livestock subcategory
using default emission factors that depend on
average annual temperature. These default
emission factors represent the range in manure
volatile solids content and in manure manage-
ment practices that would be used in each
region, as well as the difference in emissions due
to temperature. Tier 2 is a more complex method
for estimating CH
4
emissions from manure man-
agement requiring information on animal and
diet characteristics and manure management
practices. The production of volatile solids in the
manure is calculated from GEI of the animal and
digestibility of the diet, or alternatively volatile
solids can be estimated using laboratory methods.
Nitrous oxide
Manure N
2
O
Nitrous oxide is emitted both directly and indi-
rectly from livestock manure (urine and faeces)
during storage and when applied to soils and
crops or deposited on pasture during grazing.
The direct emission of N
2
O from manure depends
on the N and C content of manure, and on the
duration of the storage and type of treatment
