Energizing marginal soils – Sida for sustainable biomass production

A sustainable alternative to the cultivation of food-based energy crops is the cultivation of dedicated energy crops on marginal lands. To further increase the sustainability of energy cropping the dependency on synthetic fertilizers needs to be reduced via closed nutrient loops in the biomass production cycle.We evaluated the growth of the high potential energy plant Sida hermaphrodita (sida) on a marginal sandy soil. We compared digestate from biogas production with a commercial mineral NPK-fertilizer and an unfertilized control for a whole growth-period under outdoor conditions, with individual plants growing in large microcosms. To further increase independency from synthetically produced N-fertilizers, the legume plant Medicago sativa was intercropped to fix atmospheric N2 into the cropping system and to produce additional biomass.NPK fertilization resulted in rapid growth in the first months after planting compared to the organic digestate application, but the latter extended the vegetation period of sida by 20 days. Both fertilization treatments showed a clearly increased biomass production compared with the control plants without any fertilization. Intercropped legume plants fixed additional N into the cropping system and could increase biomass production even though they reduced the yield of sida.We conclude that marginal lands with soil characteristics that do not meet the requirements for conventional crops can be used for biomass production using perennial energy-crops such as Sida hermaphrodita in specially adapted production systems