As part of the implementation of policies related to the Nitrate
Directive of the European Union (91/676/CEE), districts (cantons) in
France have been classified in relation to their vulnerability to
water pollution by N used in agriculture. Structural Surplus Zones
(Zones d’Excedent Structurel -ZES-) have been defined as zones
where the production of N in the form of animal manure surpasses
a threshold of 170 kg ha1 per year over the spreadable area. In
Bretagne, 104 out of 187 cantons are classified as ZES. In the ZES,
livestock farms exceeding a certain production of N as animal
manure (between 12,500 and 20,000 kg per year, depending on the
district) must develop a plan for the disposal of the excess N to
reduce its environmental impact by either treating the slurry or
transferring it outside the ZES for its application to crop land (MIRE,
2004).