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Abstract :

Decisions about nitrogen fertilizer application on wheat have, for the last 40 years, been based on the balance sheet method, with the following underlying principles: non-limiting nitrogen nutrition throughout the crop cycle, and independent estimation of the various terms of the equation, to characterize soil nitrogen supply and plant nitrogen needs. Environmental pollution, changes in the qualitative requirements of the market and difficulties implementing this method have raised questions about whether it might be appropriate to switch to new ways of managing nitrogen fertilizer.

We developed a new method meeting the diverse constraints relating to nitrogen use, making the best use of available knowledge and easily applicable by users, through a 3-steps innovative design approach: a diagnosis of the use of current tools, a design phase including design workshops, production of new knowledge, a modelbased prototyping, and the testing of a prototype method.The diagnosis of uses identified several barriers to the implementation of the balance sheet method, including the need to set a target yield. This directed the design phase towards the exploration of new ways of managing nitrogen fertilizer that did not require the fixing of a target yield. The method developed is based on the regular monitoring of plant nitrogen nutrition, the toleration of periods of nitrogen deficiency that are not prejudicial and the use of decision rules taking weather conditions at the time of nitrogen application into account.

This design required the generation of new knowledge and a diversification of the resources and skills usually mobilized. This work enriches the methods for designing decision support tools and shows how a combination of 3 steps can be used to develop a tool for managing nitrogen fertilizer applications completely different from the dominant paradigm of the last 40 years, and compensating the defects of current methods.

Thèse soutenue le 10 février 2017

Co-supervision :

Jean-Marc Meynard, Marie-Hélène Jeuffroy

Jury : 

• Thierry DORE, Professeur, AgroParisTech, Paris (Président)
• Mireille NAVARRETE, Directeur de Recherche, INRA, Avignon (Rapporteur)
• Walter ROSSING, Professeur, Wageningen University & Research, Pays-bas (Rapporteur)
• Christophe DAVID, Directeur Scientifique, ISARA Lyon (Examinateur)
• Flore BARCELLINI, Professeur, CNAM, Paris (Examinatrice)
• Philippe GATE, Directeur Scientifique, Arvalis-Institut-du-végétal (Examinateur)
• Guy RICHARD, Directeur de Recherche, INRA, Orléans (Examinateur)
• Jean-Marc MEYNARD, Directeur de Recherche, INRA, Grignon (Directeur de thèse)