Minimising losses of nitrogen from UK agriculture

The nitrogen cycle is essentially ‘leaky’. Small amounts of nitrate must leach into waters, and ammonia and nitrous oxide be emitted to the atmosphere to maintain natural ecosystems. However, in many parts of the world, intensive agricultural production has contributed, with industry and vehicle use, to the global doubling of 'reactive' nitrogen (N) in the environment, resulting in eutrophication (nutrient enrichment), ecosystem change and health concerns. This has resulted in increased pressures on farmers to reduce those losses, including legislation such as the EU Nitrate Limit of 50 mg l-1, the reductions in ammonia and nitrous oxide emissions required by the UNECE Convention on long-range Transboundary Air Pollution and the all-embracing Water Framework Directive A very large amount of research has identified practices that cause large losses of N, including the particular problems of livestock farming caused by the inefficiency (<20%) with which animals transfer N in feed into saleable produce. Best Management Practices for minimising losses of N from arable and horticultural crops can be prescribed. These include calculating fertiliser requirements with a recommendation system, allowing for soil mineral N and manures applied, spreading fertilizers evenly with a properly calibrated spreader, minimising pest and disease infestation, and effective scheduling of irrigation. Computer models of the N cycle have been constructed and used as the core of new, dynamic fertiliser recommendation systems. This paper discusses the problems of maintaining productivity while reducing N losses, the impacts of recommended practices on losses, compares conventional with low input (integrated) and organic systems, and discusses options.