A whole-farm strategy to reduce environmental impacts of nitrogen.

Dutch regulations for ammonia emission require farmers to inject slurry into the soil (shallow) or to apply it in narrow bands at the surface. For one commercial dairy farm in the Netherlands it was hypothesized that its alternative farming strategy, including low-protein feeding and surface spreading, could be an equally effective tool for ammonia emission abatement. The overall objective of the research was to investigate how management at this farm is related to nitrogen (N) losses to the environment, including groundwater and surface water. Gaseous emission of ammonia and greenhouse gasses from the naturally ventilated stables were 8.1 and 3.1 kg yr(-1)AU(-1) on average using the internal tracer (SF6)-ratio method. Measurements on volatilization of ammonia from slurry application to the field using an integrated horizontal flux method and the micrometeorological mass balance method yielded relatively low values of ammonia emissions per ha (3.5-10.9 kg NH3-N ha(-1)). The mean nitrate concentration in the upper ground water was 6.7 mg L-1 for 2004 and 3.0 mg L-1 for 2005, and the half-year summer means of N in surface water were 2.3 mg N L-1 and 3.4 mg N L-1 for 2004 and 2005, respectively. Using a nutrient budget model for this farm, partly based on these findings, it was found that the calculated ammonia loss per con milk (range 5.3-7.5 kg N Mg-1) is comparable with the estimated ammonia loss of a conventional farm that applies animal slurry using prescribed technologies.