Century-Long Analysis of Nitrogen and Phosphorus Surplus in French Agriculture: Trends and Drivers

Abstract

This study provides the longest trend analysis of Nitrogen (N) and phosphorus (P) surplus in France from 1920 to 2020, modeled with the CaSSiS model at both national and departmental levels. At the national scale, the century long average annual N surplus is about 37 ± 13 kg N per ha of utilized agricultural area (UAA) per year, while P surplus averages about 9 ± 7 kg P ha UAA⁻¹ year⁻¹. However, significant periods of change correspond to important agricultural and economic events such as the World Wars and major agri-environmental reforms. Analysis of N and P use efficiency (NUE and PUE, respectively) revealed varying trends over time. NUE averaged 67%, ranging from 52% to 78%, while PUE exhibited larger fluctuations, ranging from 30% to 130%. At the departmental level, N surplus fluctuated between −15 and 140 kg N ha UAA⁻¹, and P surplus ranged from −15 to 41 kg P ha UAA⁻¹. Temporal trends revealed an increase in N surplus in 96% of departments from 1920 to 1990, followed by a decline in about 89% of departments from 1990 to 2020. P surplus increased in all departments until 1974, followed by a consistent decrease. Analysis of five contrasting French departments highlighted the impact of agricultural practices on nutrient surplus. These findings underscore the importance of tailored nutrient management strategies to achieve balanced inputs and outputs, promoting sustainable agriculture and minimizing environmental impacts. This study contributes valuable insights for informed decision-making in nutrient management policies and practices.