Ammonia emissions from intensive dairying: a comparison of contrasting systems in the United Kingdom and New Zealand

Abstract

Much of the increased atmospheric concentration of ammonia (NH 3) is derived from dairy farms. In order to better understand the potential for controlling emissions, a comparison was made of NH 3 emissions from dairy farms in the United Kingdom and New Zealand using recently derived emission factors. This desk study demonstrated distinct differences between the two farms: total N input, off-take and surplus in the UK were 1.7, 1.2 and 1.8 times greater than in New Zealand. More sources of NH 3 were identified in the UK which were, in the main, associated with the housing phase, and therefore manure generation. Total NH 3 losses were equivalent to 57 and 24 kg N ha −1 in the UK and New Zealand farms, respectively: these represented similar proportions of the total N inputs to both systems but because of stocking density in New Zealand and its overall greater milk production per ha, losses of NH 3 whether expressed per LU or unit of milk, were at least two times greater in the UK. Options for controlling emissions and their impact included improved slurry storage and application methods, efficient grazing patterns and increased N fertilizer use efficiency in the UK. Options were fewer in New Zealand, the most practical being more effective fertilizer application. In both cases, farming practices which increase N use efficiency, or improve C:N dietary balance for highly productive cows have much potential for reducing volatilization. The approach taken illustrated some important differences between the two farms and provided an easily adopted method to make assessments of NH 3 loss. Additionally, a set of indicators was derived to allow quantifiable comparisons.