In order to reduce the pollution caused by nitrates from agricultural sources, the Walloon region has established a Programme of Sustainable Nitrogen Management in Agriculture. This legislation encompasses all compulsory measures mentioned in the European Directive known as ‘Nitrate Directive’ (Directive 91/676/EEC), but its scope is larger, as it defines obligations regarding storage and management of livestock manure outside vulnerable zones. The Walloon legislation is the result of a long negotiation process and represents a common understanding between the Public powers, the farmer’s unions and the water producers, purifiers and distributors. It was launched in October, 2002. Three complementary levels are concerned: the field, the whole farm and the region. At field level, the objective is to reduce nitrate losses through leaching during winter. The farmer must put in place some “good agriculture practices”, particularly regarding authorised doses and periods of application of nitrogen fertilisers. At the whole farm level the farmer must maintain a balance between the organic nitrogen compound to be applied and his “land application capacity” (i.e.: the applicable quantity legally authorised). Every year, the “soil link rate” (LS) of each farm is calculated by the government administration, taking into account several factors: the number of animals on the farm, average values of nitrogen production per animal category, agricultural land surface available and authorised doses of nitrogen organic compound applicable. In vulnerable zones, organic nitrogen application is limited to 80 kg N/ha on arable land and 210 kg N/ha on grassland. Outside these vulnerable zones, the amount of livestock manure applied is limited to 120 kg N/ha on arable land and 210 kg N/ha on grassland. The organic nitrogen in excess of the “land application capacity” must be transferred to other farms that are able to value it.