Environmental performance indicators for nitrogen

The Centre for Agriculture and Environment (CLM) has developed 'environmental performance indicators' (EPIs) for the nitrogen surplus and the emission of nitrous oxide. The EPI for the nitrogen surplus is an element of the yardstick for mineral accounting while the ether is used in the yardstick for energy accounting. The nitrogen surplus is calculated using farm figures for inputs and outputs of nitrogen. For the emission of nitrous oxide from soils, two calculation methods have been developed, i.e. a simple and a complex method. Calculation of both EPIs has been carried out for energy cropping and for dairy farming. For energy crops, nitrogen surplus ranges from 58 kg nitrogen per ha for hemp to 196 kg nitrogen per ha for silage maize (reference crop: 40 kg nitrogen per ha). For the emission of nitrous oxide, both methods lead to similar results, ranging from 0.7 kg N2O-N per ha for miscanthus to 4.0 kg N2O-N per ha for silage maize (reference: 0.9 kg N2O-N per ha). For dairy farming, nitrous oxide is emitted directly from fertilisation of soils, including artificial fertiliser and manure, from grazing and indirectly from the purchase of cattle feed cultivated elsewhere. Total emission of nitrous oxide from dairy farms ranges from 3.5 kg N2O-N per ha to 18.9 kg N2O-N per ha. The major contribution comes from fertilisation, while emissions from urine deposition and purchase of cattle feed only add relatively small amounts. It was concluded that the complex method is more suitable to calculate the emission of nitrous oxide from soils. Mineral and energy accounting show that nitrogen surplus and emissions of nitrous oxide may be substantially reduced by improvements in nitrogen management. More research is needed to assess emission factors for nitrous oxide, and to develop management practices to reduce the emissions.