Dynamic monitoring of winter wheat N fertilization through the APPI-N method: an experimental evaluation

International audience

Inglés. APPI-N is a radical innovative method of nitrogen fertilization developed in recent years for winter wheat (Ravier et al. 2018, 2021). Compared to the traditionally used balance-sheet method, APPI-N does not require measurements of soil mineral N and a target yield forecast. It is based on the dynamic monitoring of crop Nitrogen Nutrition Index (NNI) from the end of winter to flowering stage, and on an NNI threshold trajectory that should not be crossed without risking yield loss. The objective of this new method is to maximize the Nitrogen Use Efficiency (NUE), through 2 main pillars: (i) accepting N deficiency period at the beginning of crop cycle, that is not detrimental to yield and protein content; (ii) rely on climatic conditions to decide N application dates and rates, by objectifying the risk of drought, which allow to maximize the valorization of nitrogen.Although the APPI-N method seems promising to improve NUE, an experimental evaluation of its potential was still lacking. In the SOLINAZO project, we tested the APPI-N method and compared it to the balance-sheet method on 36 plots between 2018 and 2021. NNI was monitored by an indirect indicator (chlorophyll meter), grain yield and protein content were measured, and the NUE was estimated with non-fertilized control plots. Finally, in order to assess economic and environmental performance of APPI-N, the partial margin and greenhouse gases (GHG) emissions were quantified.Results showed (i) a delay of the first N application (on average 20 days later than for the balance-sheet method) and a reduction of the total number of applications; (ii) a reduction of total N rate without significant changes in yield or grain protein content; (iii) a reduction of nitrogen losses and of GHG emissions.The APPI-N method seems promising to use nitrogen is a more efficient way: it gives users the possibility to follow plant needs and to have a direct feedback on their fertilization actions. It can also be easily adapted to technological advances, especially to monitor NNI in a less time-consuming way (visible imagery, satellites, etc.). Nevertheless, its radically innovative nature challenges farmers' habits and requires learning new ways of thinking.