Crop production for biogas and water protection-A trade-off?

Water fluxes, crop height and green area index were satisfactorily simulated. Nitrate-N loss in grassland generally was very low, staying below the critical nitrate-N load, according to the EU drinking water threshold. At optimal N input, i.e. N input required for maximum yield, maize caused a considerable nitrate-N load (48-67 kg ha−1), and it increased exponentially at higher inputs. Most of the variation of nitrate-N load among fertilizer types was explained by the proportion of fertilizer-N input as mineral N. For both grassland and maize, biogas residues had a similar nitrate leaching potential to animal manures. Maize achieved a substantially higher methane hectare yield (mN3 CH4 ha−1) than grassland. This could not overcompensate for its higher nitrate-N load, as indicated by the eco-efficiencies in terms of kg nitrate-N load per mega liter methane produced at optimal N input (maize: 7.7-14.7, grass: 0.3-2.9).