The impact of agriculture on the environment is often discussed merely in terms of pollution due to leaching of agrochemicals or to erosion of contaminated soil particles. As a matter of fact, however, more important environmental problems are due to the imbalance or the lack of closure of nutrient cycles and to the wrong choices made to this purpose. The natural role of agriculture is the re-utilization of wastes and effluents, no more congenial today for the farmers themselves. It is necessary therefore to encourage farmers to play their environmental role. The definition of sustainable agriculture does not disregard this role, but it is possible to stress the concept that agriculture, by playing this role, becomes the ground for a sustainable society.