Bioenergy provision by an alley cropping system of grassland and shrub willow hybrids: biomass, fuel characteristics and net energy yields

Abstract

In the temperate zone, alley cropping is promoted as a climate change-resilient agroforestry practice for the provision of biogenic energy carriers. However, little information is available on the potential of such cropping systems as feedstock for biofuel production. In a field trial in Central Europe, the triennial performance of alley cropping systems was assessed. The systems consisted of clover-grass, a native diversity-oriented grassland mixture and multi-rows of willows. They were compared to a willow and grassland control adjacent to the trial area. Three different conversion technologies were applied to grassland feedstock and analyzed for relevant quality parameters. Net energy balances were calculated to determine the potential of the cropping systems and the associated controls as providers of biogenic energy carriers. The grassland control had the highest triennial yield (18 t DM ha−1), whereas pure willow stands were less productive with 7 t DM ha−1. Alley cropping was intermediate with 12 t DM ha−1 on average. Net energy yield of the clover-grass based systems was highest in the grassland control for all conversion technologies, whereas values of the diversity-based systems in the control and the alley cropping system achieved similar values. This study only investigated the first 3 years after establishment, when growth rates of shrub willows were still low. Thus, more research is needed to evaluate the long-term performance of agroforestry systems with shrub willows and herbaceous crops.