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

PARALLEL SESSION 5B: METHODOLOGICAL CHALLENGES FOR CROP PRODUCTION SYSTEMS8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
2.3.3. Methods for allocations and system expansion
Economic allocation was calculated based on mean official price from 2000-2010 (Agreste database:
www.agreste.agriculture.gouv.fr). Mean official price for wheat and pea was of 129 euros ton -1 , and
150 euros ton -1 , respectively.
System expansion was carried out by replacing impacts attributed to intercropped pea by the respective
impacts estimated for sole cropped pea.
2.4. Calculations
The Land Equivalent Ratio (LER) for grain yield for pea–wheat intercrops was calculated according to De
Wit and Van den Bergh (1965). The LER is the sum of the partial LER values for wheat (LERw) and pea
(LERp):
468
GY GY
LER
GY GY
WIC PIC
LERw LERp
Eq.1
WSC
PSC
where GYWIC and GYPIC are yields of wheat and pea in the intercrops, respectively, and GYWSC and GYPSC
are the yields of wheat and pea in sole crops, respectively. LER values above 1 indicate a benefit of intercropping
over sole cropping.
Nitrogen leaching was estimated based on experimental measurements using mass balance as follows:
Nleaching = Nsoil S– Nsoil W – Nabv - Ndfa Eq.2
where:
Nleaching is the estimated quantity of leached N
Nsoil S is the N soil content observed at sowing (0–90cm soil layer)
Nsoil W is the N soil content observed in February after the leaching period (0–90cm soil layer)
Nabv is the amount of N observed in the aboveground canopy
Ndfa is the amount of N derived from air
3. Results
3.1. Estimated impacts related to wheat grain production
Estimated impacts per kg of sole cropped wheat (W100 N) were of 0.37 kg CO2 eq., 1.17 g PO4 3- eq., and
2.18 MJ eq., concerning climate change (CC), eutrophication (EU), and cumulative energy demand (CED),
respectively (fig.1). Concerning the un-fertilised intercrop (P50W50 N0), mass allocations of impacts among
co-products brought about impacts of 0.15 kg CO2 eq., 0.71 g PO4 3- eq., and 1.31 MJ eq., for CC, EU, and
CED, respectively. N-fertilisation of the intercrop increased environmental impacts by 36%, 32%, and 17%
for CC, EU, and CED, respectively (fig.1).
Methods for co-product allocation affected impacts. Concerning the un-fertilised intercrop, economic allocation
impacts were 0.14 kg CO2 eq., 0.64 g PO4 3- eq., and 1.19 MJ eq., for CC, EU, and CED, respectively.
Allocation based on the N content of grains resulted in lower impacts than for economic allocation:
0.10 kg CO2 eq., 0.48 g PO4 3- eq., and 0.90 MJ eq., for CC, EU, and CED, respectively (fig.1).
System expansion resulted in the lowest values for all impacts. In case of un-fertilised intercrops, this
method always yielded negative impacts (-0.10 kg CO2 eq., -0.68 g PO4 3- eq., and -0.88 MJ eq., for CC, EU,
and CED, respectively) (Fig.1).