Yield Gap Analysis of Young Miscanthus x Giganteus Crops: A Survey of Farmers' Fields in East Central France.

Miscanthus x giganteus is often regarded as one of the most promising crops to produce bioenergy because it is renowned for its high biomass yields, combined with low input requirements. However, its productivity has been mainly studied in experimental conditions. Our study aimed at characterizing and explaining Miscanthus x giganteus yield variability on a farmers’ field network located in east central France. It included the first three growth years of the crop, i.e. the two first harvests, since the crop was not harvested at the end of the first year. We defined and calculated a set of indicators of limiting factors that could be involved in yield variations and used the mixed-model method to identify those explaining most of the yield variation. We also studied the difference between plot yields measured on a small area (i.e. two plots of 25 m²) and commercial yields measured on whole fields. Plot yields averaged 11.2 t DM ha^-1 for the second growth year and 15.3 t DM ha^-1 for the third. These mean results concealed however a high variability: our field network included fields reaching yields close to those reported in experimental conditions (up to 22 t DM ha^-1) but also fields with very low yields (below 3 t DM ha^-1). Yields were found to be much more related to the shoot density than to the shoot mass, and particularly to the shoot density established at the end of the planting year. Fields with the lowest yields and the lowest shoot densities also had the highest weed cover. Lastly, commercial yields were on average 30% lower than plot yields. Situations specific to commercial farm scale conditions, such as field size and shape, field location and field history were shown to affect the difference between plot yields and commercial yields.