The effect of digestate fertilisation on grass biogas yield and soil properties in field-biomass-biogas-field renewable energy production approach in Lithuania

Abstract

The shift from a fossil economy to a biological economy will stimulate the demand for bio-based energy generation. One promising strategy to meet the growing demand for biomass for energy production is to re-cultivate abandoned arable land. The digestate fertilisation approach for the sake of increased biomass yields is the key strategy towards more sustainable biogas generation in many regions. To minimise digestate utilisation costs, biogas plant operators seek to spread the liquid digestate as close as possible to its storage location. The present work is focused on the evaluation of the digestate impact on the eroded agricultural soil, the improved biomass yield of semi-natural grassland biomass and its biogas potential. Three-year field experiment results indicate the positive effect of solid and liquid digestate on soil fertility and quality. The amount of dissolved organic carbon in eroded loamy Retisol increased 3.7% and 15% in soil 0–10 cm layer with fertilisation rate of 170 kg ha−1 N of liquid and solid digestate, respectively. In terms of total nitrogen, 11.6% and 20% increases were achieved using 170 kg ha−1 N of liquid and solid digestate compared to unfertilised. Furthermore, the grass fresh biomass yield was up to 3 times higher compared to the unfertilised yield. The biomethane yield of biomass from digestate-fertilised fields was higher for every fertilisation rate applied. The highest biomethane yield was for 170 kg N ha−1 liquid digestate applied, yielding 19% more biogas compared to untreated field biomass due to both increased biogas yield and increased methane content.