The effect of biogas digestion on theenvironmental impact and energy balancesin organic cropping systems using thelife-cycle assessment methodology

A life-cycle assessment (LCA) was carried out to compare the environmental performance of different organic croppingsystems with and without digestion of slurry and crop residues. The aims of the present study are: (1) to compare theenvironmental performance of organic farming dairy systems with the currently prevalent animal housing systems [solidfarmyard manure (FYM) versus liquid slurry] as the main reference systems; (2) to analyze the effect of the implementationof a biogas digestion system on the consumption of fossil fuels and production of electrical energy; (3) to quantify theeffects of the implementation of a biogas digestion system on the environment; and (4) to compare the obtained net energyyields with other means of obtaining energy by using the farmland area. The considered impact categories are greenhousegas (GHG) balances, acidification, eutrophication and groundwater pollution. LCA results indicated that total emissions insystems based on FYM are much higher than in liquid slurry systems for most of the considered impact categories. Thebenefits of digestion of stable wastes in comparison with the reference system without digestion are mainly (1) the netreduction of the emissions of GHG and (2) energy recovery from produced biogas, while the disadvantages can be higheremissions of NH3 after spreading. The effects of additional biogas digestion of biomass such as crop residues (e.g., straw ofpeas and cereals) and cover crops are: (1) an optimization of the N-cycle and therewith higher yields; (2) higher energyproduction per unit arable land; (3) a further reduction of the GHG balance; but (4) higher N-related environmental burdenslike eutrophication and acidification. The offsets of fossil fuel emissions were the largest GHG sink in most of the biogasdigestion systems. The inclusion of a biogas plant into organic cropping systems and the use of the available wastes forproduction of energy largely increased the overall productivity of the farming system and matched very well the basicprinciples of organic farming such as a high self-sufficiency of the cropping system and reducing as much as possible theenvironmental impact of farming