agreste

Agreste cahiers n° 2 - juin 2001

The surplus of agricultural nitrogen can be estimated, for a given growing season and a given geographical area, by the surplus of mineral or nitrogen fertiliser with respect to the exports contained in the crops.

The surplus of agricultural nitrogen can be estimated, for a given growing season and a given geographical area, by the surplus of mineral or nitrogen fertiliser with respect to the exports contained in the crops. After rising from 1981 to 1986, as in previous decades, the surpluses thus calculated fell noticeably from 1986 to 1994. However, they have since increased, thus eliminating most of the earlier progress. The period of declining fertiliser use corresponds to a combination of smaller doses per hectare being used on crops, increasing fallow land, and declining dairy herds. These trends can be obscured by the effects of climatic conditions in a given year, which can cause random variations in exports of crops, of grasslands or even animal wastes. The method of estimation that is presented isolates this fluctuating component of surpluses, in order to show changes in the trends.