Energy Crop (Sida Hermaphrodita) Fertilization Using Digestate under Marginal Soil Conditions: A Dose-response Experiment

Abstract

The global demand for energy security and the mitigation of climate change are the main drivers pushing the production of crops for energy purposes (energy crops). However, the cultivation of these plants can cause land use conflicts since agricultural soil is mostly used for food crop production. A sustainable alternative to the conventional cultivation of food-based energy-crops is the cultivation of non-food energy crops on marginal lands. To further increase the sustainability of energy crop cultivation systems the dependency on synthetic fertilizers needs to be reduced via closed nutrient loops in the production chain for bioenergy.In the present study Sida hermaphrodita was used to evaluate its potential as an energy crop to be grown on a marginal sandy soil in combination with a fertilization using digestate from biogas production. With this dose-response experiment we identified an optimum digestate dose of 40t ha-1 corresponding to the highest biomass production, which was compared to an equivalent dose of mineral NPK-fertilizer. Further, 240t ha-1 had lethal effects on Sida hermaphrodita. A digestate dose of 5t ha-1 showed no fertilization effect. Digestate fertilization built up a pool of soil organic matter (SOM). The slow release of nitrogen from this organic pool could serve as long term fertilization and help to limit the high risk of leaching on marginal soils. Accordingly we see a potential of biogas digestate as a sustainable alternative to mineral fertilizers for the cultivation of the energy crop Sida hermaphrodita on marginal soils.