Biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P) are naturally coupled in terrestrial ecosystems by elemental stoichiometry of plant autotrophy and of soil biologic heterotrophy. The shift from natural to cropped intensive systems led to major changes in crop land use, nutrient availability, and soil management. This chapter presents the fundamental processes of C, N, and P coupling and how the intensification of agriculture has “opened” and “decoupled” the terrestrial nutrient cycles, leading to major environmental impacts, particularly with nitrogen. Intensification of agriculture has reduced the diversity of plant species and lowered organic carbon inputs to soils, increased the N saturation of agrosystems by fertilization, and to a lesser extent P, the territorial specialization of agriculture has increased nutrient fluxes and imbalances both at regional and world scales. These major changes have modified in turn the nature and amount of plant biomass recycled to soils, the diversity and activities of soil communities, and affected the balance of nutrient mineralization to immobilization by heterotrophs. Lack of synchrony between nutrients supply and plant demand, enhanced by the simplification of crop rotations, is also a major cause of decoupling between cycles. Therefore, new farming strategies should aim, at plot scale, at diversifying crops, increasing the presence of legumes in rotations, and the annual soil occupancy by crops, and at increasing, at farm and regional scales, the complexity of cropping systems (particularly by mixing arable and livestock farming) to enhance local recycling of nutrients and decrease the use of synthetic fertilizers.< Réduire