Environmental life cycle assessment of organic grass protein from multispecies mixtures

Summary

Including grass leys in organic arable rotations has potentially several benefits such as suppression of certain weeds, increased biodiversity (i.e. pollinators), increased soil carbon sequestration and productivity among others. The biomass from the grass mixtures can be refined into protein feed concentrate for monogastrics that can partly replace imported soybean, while the fibre fraction can be used as ruminant feed or for biogas. The grass mixtures can also be used directly for biogas. Increasing diversity of the mixtures will potentially also increase the yield stability and the benefits for biodiversity (pollinators), while the number of cuts per year will also have an effect. Thus, the use of multispecies mixtures in organic arable rotation for production of protein or energy has potentially climate and biodiversity benefits. The overall environmental impact on climate and biodiversity was evaluated using life cycle assessment. Three different multispecies mixture and two cutting regimes (two or four cuts per year) was evaluated. The biomass from the two cut strategy was used for biogas directly and the biomass from the four cut strategy were refined to protein concentrate for monogastrics, while the fibre fraction was used for ruminant feed. The results showed a climate impact per ton DM were lowest for the pollinator and energy mixtures and highest for the protein mixtures. However, when measured per ton protein, the climate impact of the biomass from the two cut strategy was highest for the energy mixture followed by the protein and the pollinator mixtures. The hotspots in the agricultural production was the nitrous oxide emissions and the soil carbon changes. The climate impact of protein concentrates from the multispecies mixtures were lower than imported organic soybean. The hotspot in the production of the protein concentrates was the agricultural production, transport and energy use. The sensitivity analysis showed that increasing the transport distance to 50 km for biomass going to the biorefinery, would increase the climate impact of the protein concentrate above the climate impact of imported soybean. Likewise, the sensitivity analysis showed that increasing the energy use for processing 2.5 times would increase the climate impact of the protein concentrate to the level of the imported soybeans.