Ammonia volatilization from dairy farming systems in temperate areas: a review

Ammonia (NH₃) emissions from dairy farm systems cause environmental problems. This paper reviews and quantifies the major loss routes of NH₃ in dairy farms. Furthermore, management options are discussed that reduce NH₃ losses.Losses of NH₃ occur during slurry application, housing, slurry storage, grazing, fertilizer application and from crops, in descending order of importance. Animal waste is the major source in four of the six cases. This ranking varies between farms and between countries, depending on environmental conditions and management practices. Total NH₃ losses range from 17 to 46 kg N cow yr^-1, reflecting the variability in amount and composition of animal excreta (urine + faeces), management of the slurry and soil and environmental conditions. The amount and composition of urine and faeces depend on N tranformations in the digestive track of the cow. Of the major nitrogen compounds excreted urea has the highest potential for NH₃ volatilization followed by allantoin, uric acid and creatinine in decreasing order. Creatine, xanthine and hypoxanthine have a low NH₃ volatilization potential.Reducing the excretion of urea and urea like products by optimizing N Intake (NI) and N Retention (NR) is one way of decreasing NH₃ losses. Improvement is possible since NR is about 20% of NI in practice, whereas 43% is theoretically possible. The second solution is to reduce the rate of NH₃ loss by technical means like direct incorporation of slurry into the soil, dilution or acidification of slurry, covering of the slurry storage and/or acidification or dilution of slurry in the storage. These techniques have been known for a long time and now become available on a large scale in practice. Reducing the surface area per cow in the shed and sprinkling floors with water to remove and to dilute urine also decreases NH₃ loss.Reducing NH₃ loss requires a whole farm system approach, because it shows how intervening in one part may affect NH₃ losses in other parts of the system. Reducing NH₃ loss may increase nitrate leaching and denitrification. To prevent this, the achieved reduction in NH₃ loss should lead to a reduction of total N input of fertilizers, concentrates and forage on the N budget of the farm, which is possible as a reduction of NH₃ loss improves the N fertilizing value of slurry. Model calculations showed great scope for reducing NH₃ losses on dairy farms by improved management. Up to three fold reductions in NH₃ loss are possible together with marked reductions in mineral fertilizer usage. The rate at which improved management techniques, will be introduced in practice depends on legislation, the applicability of new techniques and the expected increase in net production costs. To comply with environmental targets requires a huge effort of farmers with associated high costs.