Economic and Environmental Analysis of Maize Inoculation by Plant Growth Promoting Rhizobacteria in the French Rhône-Alpes Region

In the context of global agricultural challenges, plant growth-promoting rhizobacteria from the genus Azospirillum used to inoculate cereal seeds have attracted a lot of attention, mostly for their expected agronomic benefits. This study assesses the economic impact on farmers' profit from maize inoculation, along with the environmental impact in term of greenhouse gas emissions, in the Rhône-Alpes region of France. Yield-to‑nitrogen relationships predicted by the STICS crop model were modified to simulate the effect of inoculation on maize yield, and four inoculation costs (0, 20, 40 and 60 euros/ha) were considered to assess the private economic effect of inoculation. The environmental impact was assessed using a Bouwman-type N2O emission function, modified to account for the inoculation effect on soil N2O production according to soil characteristics. Yield and N2O emission functions were then implemented in the AROPAj farm-type, supply side-oriented model. Several scenarios were considered and probability density functions were selected for the yield function parameters according to field trial results. Our results show that, mainly due to a decrease in fertilizer use rather than to an increase in yield, farming systems in the Rhône-Alpes region could benefit from maize inoculation if the inoculation cost is lower than €20/ha. Regardless of inoculation cost, maize inoculation might reduce the amount of synthetic fertilizer used on farmlands. However, the private economic benefits could be lower if maize is cultivated on soils with a high carbon content, where inoculation increases N2O emission. In these types of soils, greenhouse gas emissions at the regional level could increase by 2 to 5%.