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Description
INTRODUCTION
For several decades in France, nitrogen (N) fertilization reasoning has been based on the principle of the "balance sheet" method. This method comes up against strong implementation limitations (Ravier et al., 2016), 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 in wheat, CHN-conduite, which relies on a mechanistic crop model (CHN) to access plant N nutrition levels in real time and forecast canopy N requirements. CHN allows to simulate the development, growth and N nutrition status of a wheat crop on a daily basis in response to its environment using a dynamic approach. The innovative near-real-time coupling of CHN with data from on-board satellite sensors provides a highly accurate diagnosis of wheat's N nutrition status, improving the accuracy of crop N requirement projections. CHN-conduite considers several elements in the reasoning of tactical advice. N requirements are established on the basis of a floor nitrogen nutrition index trajectory. The fractioning of N inputs does not follow an a priori defined strategy, in favor of a multi-criteria reasoning method that is more integrative of annual variability. The aim of this study is to evaluate the agronomic performance of CHN-conduite under field conditions.
MATERIAL AND METHODS
This study relies on a French network of 27 field trials of winter bread wheat (Triticum aestivum L.) conducted in 2023. Nitrogen management based on the balance sheet method was compared with that based on the CHN-conduite tool. Measurements of grain yield and grain protein concentration were performed at harvest to compare the two practices. The total N rate applied in each treatment was also recorded. These data were used to calculate a nitrogen net profit margin, incorporating several scenarios for N fertilizer prices (from 1.3 to 2.7 €kgN-1) and grain selling prices (from 230 to 350 €t-1). A remuneration scale for grain protein concentration was also used for this evaluation.
RESULTS
Compared with the balance sheet method, integral management of N fertilization using the CHN-conduite tool 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 = 0.12NS) and without penalizing grain protein concentration (+0.2%, p-value = 0.23NS). 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 observed across the network ranges from 77 to 109 €ha-1.
DISCUSSION – CONCLUSION
The main factor in the success of a N fertilization strategy is the ability to integrate the effect of the climatic year on the crop's N requirements. Beyond the direct effect of the total N rate, the tactic of splitting is also very important in maximizing nitrogen use efficiency. While an a priori calculation of the total N rate, as proposed by the balance sheet method, allows only very few adjustments during season, the integral management of N fertilization is extremely reactive to growth conditions. Growth projections, which determine wheat's nitrogen requirements, are regularly updated during the campaign to incorporate the real year's climate. In addition, by coupling CHN with on-board satellite sensors, the impact of non-climate-related accidents can be taken into account when revising N requirements. The tool's decision rules also enable to optimize intervention dates, and adjust the recommended N rates to the dynamics of the wheat's N demand at each application. The combination of these different solutions in the CHN-conduite tool gives it an enhanced ability to propose an optimized fertilization strategy. The results confirm the potential of this new approach. It also opens up prospects for future developments, which will make it possible to optimize fertilization strategies by integrating new optimization constraints, such as reducing the crop's carbon footprint.
REFERENCES
Ravier, C., Jeuffroy, M. H., & Meynard, J. M. (2016). Mismatch between a science-based decision tool and its use: The case of the balance-sheet method for nitrogen fertilization in France. NJAS-Wageningen Journal of Life Sciences, 79, 31-40.
| Keywords | Wheat;Management tool;Nitrogen use efficiency |
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