For several decades in France, nitrogen (N) fertilization reasoning for wheat crops has been based on the principle of the "balance sheet" method. This method comes up against strong implementation limitations (e.g. difficulty of estimating grain yield objective a priori), and a lack of adaptability in the face of climatic hazards.

This observation has motivated the emergence of a new concept of "integral management” of N fertilization, which avoids a priori estimates of forecast N rate in favor of reasoning based on instantaneous plant needs. Since 2017, ARVALIS has been developing an integral management tool of N fertilization for bread wheat, called CHN-conduite, which relies on a mechanistic crop model (CHN) to access plant N nutrition levels in real time and forecast crop N requirement.

The innovative near-real-time coupling of CHN with data from on-board satellite sensors provides a highly accurate diagnosis of crop's N nutrition status, further improving the accuracy of crop N requirement projections. An on-farm French experimental network composed of 27 field trials of winter bread wheat (Triticum aestivum L.) was conducted in 2023 to evaluate the agronomic performance of CHN-conduite under field conditions.

Compared with the balance sheet method, integral management of N fertilization significantly improved grain yield by 0.25 tha-1 (p-value = 0.03) without increasing the nitrogen rate applied (-12.1 kgNha-1, p-value = 0.12) and without penalizing grain protein concentration (+0.2%, p-value = 0.23). Producing more grain with higher protein concentration using less nitrogen fertilizer mechanically improves the nitrogen net profit margin.

Depending on the combination of fertilizer purchase price and grain selling price scenarios, the average gain ranges from 77 to 109 €ha-1. The results confirm the potential of this new approach. It also opens prospects for future developments, making it possible to optimize fertilization strategies by integrating new optimization constraints, such as crop's carbon footprint.