ANALYSIS OF AGRARIAN METABOLISM IN FRANCE FROM 1850 TO 2050

Introduction

This page presents and documents the work I am doing during my PhD. It started in October 2023 and is co-supervised by Lauriane Mouysset at CIRED and Olivier Vidal at ISTERRE. As part of my research, I am participating in the work of the Agriculture team at The Shift Project.

Context

My doctoral project, in collaboration with The Shift Project, aims to study the material and energy exchanges between human systems, such as agriculture, and the environment, in order to understand the development models of societies and to determine how to build a viable and sustainable future. More specifically, I focus on physical economics, i.e. the flows of materials and energy in socio-economic systems, particularly in agriculture. The analysis of these flows is called metabolism. This has allowed for the analysis of major metabolic transitions in our societies, such as the shift from early 20th-century mixed crop-livestock farming to current industrial and intensive agriculture, for example, the replacement of animal traction by tractors.

GRAFS-E

Representing nitrogen physical flows in agricultural systems

The model

GRAFS-E (Generalized Representation of Agro-Food Systems – Extended) is an enhanced version of the GRAFS model, which already tracked nitrogen flows in French agriculture. While GRAFS was limited to four main compartments (cereals-grasslands, ruminants, monogastrics, and population), GRAFS-E now breaks the system into 66 distinct objects: 35 crops (cereals, legumes, forages, etc.), 6 types of livestock, 2 population categories, the Haber-Bosch industrial process, several external sectors, and seven environmental reservoirs. For each year and each of the 33 metropolitan regions of France studied between 1852 and 2014, it produces a 66 × 66 matrix quantifying, in kilotonnes of nitrogen per year, all transfers between these objects. This fine resolution allows, for example, distinguishing the share of nitrogen recycled from cattle to grasslands, the dependence of wheat on Haber-Bosch processes, or the atmospheric and aquatic losses associated with each crop.

To generate these detailed flows, the model relies on new data (areas, yields, animal and human diets) and an optimization module that dynamically allocates plant production between human food, animal feed, and exports/imports, while respecting target dietary patterns and regional trade balances. This approach retains the simplicity of use of the original GRAFS model (few parameters, easily accessible data), while providing a much more nuanced view of nutrient recycling loops, external dependencies, and nitrogen leakage points. GRAFS-E thus becomes a tool of choice for analyzing the retrospective nitrogen metabolism in French agro-systems, comparing regions, testing dietary or agricultural practice change scenarios, and more broadly informing reflections on sustainability and circularity in agriculture.

Methodology paper submitted. Please contact me for the pre-print.