Nitrogen Cycling in Grassland Systems

Keywords: Ammonia volatilisation, Grassland, Nitrogen cycle, Nitrogen leaching, Nitrous oxide, Nitric oxide.

Agricultural intensification of production from grassland has led to serious imbalances between inputs of nitrogen (N) (in purchased fertilisers, feeds and atmospheric deposition) and outputs (mainly milk and meat). Large quantities of N are recycled to land during grazing or application of organic manures. Excess nutrients are lost into the wider environment with consequences for water, soil and atmospheric quality. The processes leading to loss of N are described and strategies to minimise losses are discussed. To meet current and/or proposed environmental targets with respect to N emissions, farmers are under pressure to better target N inputs to meet crop and livestock requirements and to improve management of farm wastes with respect to storage and application. Combining a range of management strategies has a significant impact on the flow and excesses of N in grassland systems. However, the implementation of improved management strategies will be dependent on legislation, the applicability of new techniques and the financial implications.

Dr Catherine J. Watson, Department of Agriculture and Rural Development, Belfast, and The Queen’s University of Belfast, Northern Ireland, UK

36 pages, 10 figures, 3 tables, 85 refs.