LCA Food 2012 in Saint Malo, France! - Manifestations et colloques ...

PARALLEL SESSION 3C: SHEEP AND DAIRY PRODUCTION SYSTEMS 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
Figure 1. Effects of site class and N application rate on grass DM yield
The total nitrogen available annually to the grass crop is:
N N N N N N , Eq. 7
a
atm
c
f
s
e
where Natm is the atmospheric nitrogen deposition, which ranges from 15-35 kgN/ha, Nc is the nitrogen fixed
by the clover proportion, Nf is the fertiliser N applied, Ns is the nitrogen surplus not leached or denitrified
over the winter, Ne is the nitrogen in grazed animal excreta, which is not lost.
The N content of the grass (gN) is a function of the N available.
gN =20.14+0.0136(Na-Natm) Eq. 8
The total N taken up by the crop is thus gNYGDM. The balance is thus at risk of loss to air and water. The
proportions emitted to air and water are given by Sandars et al., (2003). When grazing, 20% of the dry matter
yield is assumed to be spoilt by trampling and defoliation and thus unavailable for consumption by the animal
and returned as organic matter to the soil. When grazing, sheep utilise about 6% of forage N and the
balance is excreted. Of the excreted proportion, 70% is urine and 10% of the dung is soluble. 15% of this
soluble N is volatised as ammonia and the balance of excreted N becomes incrementally available to crops,
Ne. This system of equations is solved (iteratively) for Na and the resulting Nf were found to be comparable
with typical values of fertiliser application as found in the British Survey of Fertiliser Practice (BSFP, 2005).
The proportions of grass productivities to sheep types was described by Williams et al., (2006). This also
describes other managerial inputs to grassland, e.g. reseeding rates and silage harvesting.
2.5 Other LCI data
LCI data, such as the burdens of concentrate production and direct management energy requirements came
from Williams et al., (2006). Emissions of ammonia were calculated from N excretion (NEX) at grazing and
in housing using values from the UK ammonia inventory (Misselbrook et al., 2010). Nitrous oxide emissions
from NEX during grazing followed the IPPC (2006). Nitrous oxide and methane emissions from manure management
were derived from the UK 1997 inventories for GHG emissions (Sneath, 1997, Chadwick, 1997).
Enteric methane was calculated from the IPCC (2006) Tier 2 formula in which an average gross energy density
of 18.4 MJ/kg DM was used (McDonald et al., 2011).
2.6 Implementation
The model was implemented in Microsoft Excel, using code in VBA for Applications to solve the equations.
The results were expressed as LCIs using the IPCC (2007) coefficients for GWP and the CML coefficients
for other impacts.
2.7 Scenarios
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