In pastoral soils, NH 3 and N 2 O gases are generated from N originating from dung, urine, biologically fixed N 2 , and fertiliser. The amount of these gaseous emissions depends on complex interactions between soil properties, climatic factors, and agricultural practices. In this review paper, the animal-excretal inputs and farm-effluent applications to New Zealand pastures are quantified. Data from overseas and New Zealand studies on CH 4 , NH 3 , and N 2 O emissions from excretal deposition and animal effluents, and the factors affecting these emissions, are synthesised with an aim to improve the New Zealand estimates of emissions from these sources. The practical implications of these emissions are described in relation to environmental impacts and management strategies for reducing these emissions.Keywords ammonia; best management practices; effluent; grazed pasture; manure slurry; methane; nitrous oxide Abstract The agricultural sector in New Zealand is the major contributor to ammonia (NH 3 ), nitrous oxide (N 2 O), and methane (CH 4 ) emissions to the atmosphere. These gases cause environmental degradation through their effects on soil acidification, eutrophication, and stratospheric ozone depletion. With its strong agricultural base and relatively low level of heavy industrial activity, New Zealand is unique in having a greenhouse-gas-emissions inventory dominated by the agricultural trace gases, CH 4 and N 2 O, instead of carbon dioxide which dominates in most other countries. About 96% of this anthropogenic CH 4 is emitted by ruminant animals as a byproduct during the process of enteric fermentation. Methane is also produced by anaerobic fermentation of animal manure and many other organic substrates.

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While irrigation of farm dairy effluent (FDE) to land is becoming popular in New Zealand, it can lead to increased emissions of the greenhouse gas nitrous oxide (N 2 O). This paper reports the results from trials on N 2 O emissions from irrigation of FDE to two dairy-grazed pastures on two poorly drained siltloam soils located at Waikato and Manawatu, New Zealand. These pasture soils were periodically irrigated with FDE under contrasting soil moisture conditions with water-filled pore-space (WFPS) ranging between 26% and 94%. Nitrous oxide emissions were measured from the FDE irrigated and unirrigated sites using large numbers of static chambers (12-20). Irrigation of FDE generally increased N 2 O emissions compared to the control. N 2 O emissions varied with changes in climatic conditions and soil WFPS. Overall N 2 O emissions from effluent-derived N ranged between 0.01% and 4.93% depending on irrigation time and soil WFPS. Lower N 2 O emissions from FDE were attributable to very low soil WFPS conditions during the dry seasons. Higher N 2 O emissions were measured from application of FDE to a recently grazed pasture on wet soil. Our results suggest strategic application of FDE during dry summer and autumn seasons can reduce N 2 O emissions from application of FDE. Delaying effluentirrigation after grazing events could further reduce N 2 O emissions by reducing the levels of surplus mineral-N.