Analysis of young Miscanthus x giganteus yield variability: 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 young M.giganteus yield variability on a farmers' field network located in the supply area of a cooperative society in east central France. It included the first three growth years of the crop. 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. Commercial yields averaged 8.1 and 12.8 t DM ha(-1) for the second and third growth year, respectively. However, these mean results concealed a high variability, ranging from 3 to 19 t DM ha(-1). Commercial yields, measured on whole fields, were on average 20% lower than plot yields, measured on a small area (two plots of 25 m(2)). Yields were found to be much more related to shoot density than to shoot mass, and particularly to the shoot density established at the end of the planting year. We highlighted that planting success was decisive and was built during the whole plantation year. Fields with the lowest yields also had the highest weed cover, which was influenced by the distance between the field and the farmhouse, the preceding crop and the soil type. Our findings show that growing young M.giganteus on farmers' fields involves limiting factors different from those commonly reported in the literature for experimental conditions and they could be useful to assess the economic and environmental impacts of growing M.giganteus on farmers' fields. They could also stimulate the discussion about growing bioenergy crops on marginal lands.