Intérêts et limites des différents couverts fourragers et pratiques associées vis-à-vis de l'environnement. Analyse bibliographique

The premium for the maintenance of extensive animal farming systems (PMSEE) was institued, among other measures in favour of the farm environment, in order to support the extensive systems of animal farming supposed to protect trough their practices the ecologiacl potential of the grass covers. The validity of this claim is based primarly on the environmental relevance of the maintenance of the grassland covers, in comparison with other forage covers. The main forage covers were therefore compared with respect to the environment, taking into consideration the biodiversity of the flora and the bird fauna, the quality of the water, and the sensitiveness to erosion. This study confirmed that there exists a hierarchy among the various covers as regards their environmental impact : maize, annual forage crops, grass leys and legume leys, permanent pastures, grasslands subjected to strong ecological constraints ; on the whole, it was observed that biodiversity increased as the risks of pollution and erosion diminished. Beyond this grading however, the study showed also that efficient agricultural practices could modify significantly the results, so much so that it was recommended to include them in the assessment of the environmental impact of the various forage covers. / Les principaux couverts fourragers ont été comparés du point de vue de la biodiversité végétale et avifaunistique, de la qualité de l'eau et de la sensibilité à l'érosion. L'étude confirme une hiérarchie de l'intérêt environmental des différents couverts (maïs, cultures fouragères annuelles, prairies temporaires et artificielles, prairies permanentes, milieux herbacé soumis à des contraintes écologiques fortes), qui se traduit globalement par une croissance de la biodiversité et une diminution des risques de pollution et d'érosion. Cependant, au-delà de ce classement, les pratiques agricoles ont une influence nette ; il est recommandé de les intégrer dans l'appréciation de l'impact environmental des différents couverts fourragers.