Agriculture Reference
In-Depth Information
a
CO
2
Manure applied to land
c
CO
2
b
CH
4
CH
4
CO
2
N
2
O
N
2
O
Synthetic N fert
N
2
O
CO
2
Stored manure
CH
4
N
2
O
Mineralized
N
Crop
residue N
CH
4
N
2
O
N
2
O
Manure on pasture
Direct emission
a Energy use emissions due to manure spreading (fuel use)
b Energy use emissions due to cropping (fuel use, herbicide manufacturing,
phosphorus fertilizer production)
c Energy use emissions due to nitrogen fertilizer production
Indirect emission
Storage
Nitrogen input
System transfer
Fig. 14.2.
An example of how greenhouse gas emissions and removals can be estimated for a beef farm
using the whole-farm model Holos (http://www.agr.gc.ca/holos-ghg). The model calculates enteric CH
4
,
manure-derived CH
4
and N
2
O, emissions for soil-derived N
2
O, CO
2
from on-farm energy use and the
manufacturing of fertilizer and herbicide, and CO
2
emission/removal from management-induced changes
in soil carbon stocks (Little
et al
., 2008).
majority of this emission. Additionally, CH
4
arises from manure, and accounts for a signifi-
cant proportion of emissions for non-ruminant
production, especially where liquid manure stor-
age systems predominate.
meet energy requirements is then estimated tak-
ing into account the energy density of the diet.
The default Ym value (IPCC, 2006) for mature
dairy and beef cattle, sheep and buffalo is 0.065
(range: 0.055-0.075), with the exception of
feedlot cattle consuming diets containing more
than 90% concentrate, in which case the Ym is
0.03 (range: 0.02-0.04). When highly digesti-
ble feed is used, the lower bounds of the Ym
range should be utilized and conversely, when
feed with lower digestibility is used, the higher
bounds are more appropriate.
Using a tier 2 approach, enteric CH
4
can
be predicted using country-specific methodology.
A number of empirical prediction equations that
account for differences in DMI of the animal and
the chemical composition of the ration have
been proposed, with some listed in Table 14.4.
Although many prediction equations are avail-
able, none is entirely satisfactory because when
evaluated using independent databases, most
have been found to have a high prediction error
(Ellis
et al
., 2010; Alemu
et al
., 2011).
Enteric CH
4
The IPCC (2006) tier 1 approach to estimating
enteric CH
4
uses default emission factors (kg CH
4
per animal per year) that differ for dairy cows
and other cattle and by geographical location,
while the more advanced tier 2 and 3 approaches
account for differences in animal productivity
and feed quality. Tier 2 methodology estimates
enteric CH
4
emissions by calculating gross
energy intake (GEI) of the animal, which is then
multiplied by a CH
4
conversion factor (Ym). The
GEI of the animal can be estimated from dry
matter intake (DMI) or if the intake is unknown,
from the net energy requirements of the animal
for maintenance, activity, growth, pregnancy
and lactation as appropriate. The GEI required to
