The assessment of Azodyn-Org model for managing nitrogen fertilization of organic winter wheat

In organic wheat, nitrogen is one of the key limiting factors responsible for irregular productivity and low quality. On arable farms, the decreasing use of N-organic sources such as forage legumes, manures and composts relative to mixed-farms requires the development of suitable fertility strategies based on the use of off-farm organic fertilizers. The Azodyn crop model was previously adapted to organic fertilization and evaluated on various field trials in order to predict grain yield, grain protein content and soil mineral N at harvest. This paper analyses the value of Azodyn-Org as a decision-tool for managing N fertilization by (1) evaluating the economic benefits of an organic N application and (2) selecting optimal fertilization strategies according to farmers' constraints and conditions. It appears that Azodyn-Org is relevant for selecting appropriate strategies in various conditions only if the multiple limiting factors (e.g. weeds, diseases, soil compaction) effect on yield was well predicted. In these conditions, its use could allow to identify the fields where an organic N application is profitable, through rule-based simulations. The development of an early risk-assessment method to predict the effect of major limiting factors is required before providing this tool to users. Other methodological elements of model-based explorations are addressed in the discussion.