Dairy farms exhibit large nitrogen (N) fluxes throughout the soil/plant/animal system. These fluxes increase with increasing N inputs and farming intensity, and can lead to significant N losses into the environment. Under New Zealand grazed pastoral systems, the N losses occur predominantly from animal urine. Nitrogen can impact on water quality for human consumption or for aesthetics, recreational use and fisheries via enhanced aquatic plant or algae growth. In this paper, N flows in dairy farms in New Zealand are compared with those in the European Union (EU), where dairy farming is generally more intensive. In the EU, legislation is being used to reduce N losses from intensive dairy farming in nitrate sensitive areas through defined maximum rates of manure application. Progressive reduction in these rates will potentially reduce stocking rates on intensive EU farms such as in the Netherlands, where taxation of farm N surpluses is also used as a deterrent. New Zealand has a lower average farming intensity and lower N losses to the environment than in intensive EU farms. However, farmlet systems research has shown that high N inputs of c. 400 kg N/ha/yr can increase nitrate-N concentration in groundwater by up to twice the recommended maximum for drinking water. In nitrate sensitive areas, such as around Lake Taupo, it is desirable to minimise nitrate leaching and the associated lateral movement to surface water bodies. A range of on-farm options are discussed including limiting external N inputs, increasing N use efficiency via lower protein feed sources, reducing farm dairy effluent N losses, and avoiding direct deposition of excreta to land in autumn/winter using grazing-off or feed-pad systems. Off-farm, there is potential to intercept leached nitrate before it enters surface waters via riparian strips or trenches, or in-stream removal by aquatic plants. In nitrate sensitive areas, there is a need to use a whole catchment approach by examining all contributions to nitrate leaching and not simply targeting one agricultural practice such as dairy farming.
Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 256-260, 2000
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