Environmental Impacts of Nitrogen and Phosphorus Cycling in Grassland Systems

Abstract

Agricultural intensification of grassland has led to serious imbalances between inputs of nutrients (in purchased fertilizers, feeds and atmospheric deposition) and outputs (mainly milk and meat). Excess nutrients are lost into the wider environment with consequences for soil, water and atmospheric quality. This paper examines the environmental impacts of nitrogen and phosphorus use by the grassland-based agricultural industry of Northern Ireland. Results are presented from a recently completed experimental programme, which was undertaken to define the losses associated with nitrogen inputs to grazed grassland. Also examined is the contention that P use in grassland agriculture is now the major cause of the P enrichment of Lough Neagh, the largest lake in the British Isles. A combination of strategies involving fertilizer management, manure management and dietary manipulation can have a significant impact on the flow and excesses of N and P in grassland systems. However, the rate at which improved management strategies will be introduced in practice depends on regulatory controls, the applicability of new techniques and the financial implications.