Agriculture Reference
In-Depth Information
For the two French agricultural areas supplying food to Paris, the es-
timated environmental losses of nitrogen are estimated at 25 kgNcapita
−1
yr
−1
, i.e. fi ve times the load discharged as urban wastewater by one inhabit-
ant. The largest part (92 %) of these losses occurs in the livestock farming
supply territory. Admittedly, because some surplus vegetal production of
this territory is exported to other regions, a fraction of the losses occurring
there should be ascribed to the population of these regions.
3.4 A LOCAL AND ORGANIC FARMING SCENARIO FOR THE
SEINE WATERSHED
Thieu et al. (2010b) have shown that organic agriculture, if generalised to
the entire agriculture area of the Seine watershed, has the potential to re-
store nitrogen contamination to a level below the ecological water resourc-
es standards. In order to explore the potential of reducing the nitrogen
imprint of the Paris food supply, we constructed a hypothetical scenario
based on the following constraints:
The organic and local scenario (OrgLoc) fi rst requires that most of the
food supply be produced within the limits of the Seine watershed, Paris's
traditional food-producing hinterland. This necessarily implies restoring
livestock farming within the area. The scenario assumes, however, that
this livestock be reared with only local feed: no import of proteins from
outside the Seine watershed limits would be allowed. To calculate the feed
consumed by this livestock, we used a nitrogen conversion ratio of 17
%, the current average value calculated for the Brittany-Normandy-Nord-
Pas-de-Calais regions.
The scenario also assumes organic agricultural practices, implying no
use of synthetic fertilisers, all the fertilisation of arable land being ensured
through symbiotic nitrogen fi xation and manure application. Our calcula-
tions assume that the currently observed relationship between yield and total
fertilisation shown in Fig. 2 also holds for organic practises. This assumption
implies that at a similar fertilisation rate, whether the fertilisation is organic
or mineral, the yields are identical. In other words, the often observed lower
yields of organic vs. conventional farming are the results of lower fertilisa-
tion rather any other difference. The upper relationship illustrated in Fig. 2
