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

PARALLEL SESSION 4C: CROP PRODUCTION SYSTEMS 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
fertiliser production for FE and MD. It also evidenced a high contribution of energy use for irrigation, similarly
to cluster 4. P17 and P40 (the paragons of clusters 3 and 4, respectively) showed similar impacts for
most categories, except for TA, FE, ME, TET and FET for which the impacts of P40 were significantly
lower. The greater impacts of P17 was due to pesticide applications (TET and FET), N,P,K-fertiliser manufacturing
and nitrate emissions (TA, FE and ME).
4. Discussion
4. 1. Characteristics of the types of cropping systems with regard to field selection
The diversity of horticultural cropping systems in the Tropics in general and in our context of study in
particular led us to infer that the associated environmental impacts would vary greatly between individual
fields. To assess the environmental impacts of out-of-season tomato cropping systems in Benin, we selected
a large sample of 12 fields over 50 and assumed it was large enough to represent the whole population. This
selection was guided by local expert knowledge and included geographical location (urban/peri-urban) and
irrigation system (manual/mechanised). Our principal component analysis showed that individual fields were
all different. However, by applying the AHC approach, we could group the population into four clusters defined
each by one representative fields (the paragon) showing a typical profile of the whole cluster in terms
of environmental impacts.
Looking in more detail, the first driver was energy use for irrigation, as reflected by dimension 1 of the PCA
(making up 50% of the variability). Energy use for irrigation was also responsible for the first dimension,
grouping C1 and C2 apart from C3 and C4. Soil type contributed to this effect, as the impact of energy use
for irrigation was higher on sandy soils. These findings support the relevance of our initial typology based on
irrigation systems. It also emphasized the need to include soil type as well as an important criterion to identify
representative cropping systems. Geographical location was correlated to the variability explained by
dimension 2. Farmers around Cotonou (urban area) have more intensive practices in terms of fertilisation and
crop protection than the average population. These findings suggest that practices are more intensive in urban
areas, due to scarcity of agricultural land. When assessing the environmental impacts of out-of-season
tomato cropping systems in Benin, both urban and peri-urban systems need to be addressed as their environmental
impacts are significantly different.
In addition to the expected sources of variability identified a priori, the AHC evidenced other cropping systems
specificities. Based on the analysis of clusters presented in table 3, we could dissociate extensive (C1
and C3) from intensive (C2 and C4) cropping system types and identify the source of intensification: irrigation
system (C4) or pesticides and fertilisers (C3). We also demonstrated a possible inconsistency between
yields and practices intensity, highlighting the actual risk due to pest pressure and the question of rate of
return. This observation is quite specific to horticultural crops grown in tropical peri-urban areas and clearly
questions the choice of the most relevant functional unit for such systems. Finally, we also highlighted inconsistencies
resulting in methodological weaknesses discussed in the following section.
Table 3. Environmental and agronomical analysis of clusters and subsequent outcomes for a better understanding
of cropping systems
Environmental impact variability
C1 Lower than P38
C3
C2
↑ impact of irrigation system
and NPK production
↑ impact of nitrogen emissions
↑ impact of insecticides and
nitrogen emissions
C4 ↑↑ impact of irrigation
Agronomical performances
(*not statistically significant) Main outcomes
- Short crop length
- Yield losses due to biotic &
abiotic causes*
- High mineral fertiliser rates
- Yield losses due to pest
pressure*
- High insecticide &fertiliser
application number
- Early planting dates
- High use of pump
- Large water supplied
2 strategies
- Low investment strategy, rate of return?
- Early crop failure
1 conclusion
Intensive practices ≠ high yields
Investments = risk
2 conclusions
- Intensive practices ≠ technical irrigation infrastructures
- Early planting = large use of insecticides
2 questions
- Valorisation of investments in irrigation system?
- Effect of water supply on impact of nitrogen emissions?
4.2. Implications of LCA impacts variability in the refining of methods and data collection
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