Nitrification rates and associated nitrous oxide emissions were measured in aerobic incubations of a range of soils from field trials within the National Agricultural Nitrous Oxide Research Program. Together with data that were collated from the literature, it was concluded that site-specific parameterisation of models is justified and further work is warranted to develop model algorithms that take into account known drivers.

In an irrigated wheat crop, reducing the soil moisture deficit and using the nitrification inhibitor, 3,4-dimethylpyrazole phosphate, were the most effective in achieving N₂O mitigation when combined. The majority of N₂O emissions occurred immediately after irrigation. Half of the plant N and 53–87% of N₂O were derived from non-fertiliser sources in soil, highlighting the opportunity to further exploit this valuable N pool.

Over recent years, there has been growing evidence of a non-linear, exponential relationship between N fertiliser application rate and N₂O emission. Likewise, we observed a non-linear exponential response of N₂O emissions to increasing N fertiliser rates in a typical cotton–fallow rotation. We conclude that an exponential model may be more appropriate for estimating N₂O emission from cotton cropping systems in Australia.

In this study, we investigated N₂O flux from apples and cherry cropping systems in two predominant growing regions. Estimated from manual chamber measurements over a 12-month period, the average daily emissions were very low, ranging from 0.78 g N₂O-N ha^–1 day^–1 to 1.86 g N₂O-N ha^–1 day^–1. These emissions were among the lowest recorded for an Australian agricultural industry, most likely due to low rates of N fertiliser, cool temperate growing conditions and highly efficient drip irrigation systems.

A 4-year rotational experiment with wheat–canola–grain legumes–wheat in sequence was established at Wagga Wagga, NSW, Australia. The daily N₂O emission rate was low under a canola crop, ranging between –0.81 and 6.71 g N₂O-N/ha.day. The annual cumulative N₂O-N emitted was 175.6 and 224.3 g N₂O-N/ha under 0 and 100 kg N/ha treatments respectively. Tillage does not increase N₂O emissions in this semiarid environment of south-eastern Australia.

Greenhouse gas emissions from nitrogen fertilisers are a significant contributor to Australia’s national N₂O budget. Mitigation of these emissions can be achieved with EEFs. However, EEFs target different loss processes, and decreasing the loss from one pathway may simply transfer it to another. Herein, a nitrification inhibitor effectively decreased N₂O emissions relative to granular urea, whereas a urease inhibitor, which targets NH₃ loss, increased N₂O emissions and a fine particle spray had limited effects over the low-emission period. Biomass productivity benefits were difficult to achieve with the EEFs, reflecting the relatively low loss via N₂O emissions, presence of sufficient N for growth in the pasture system, and influence of climate on nitrogen loss and pasture productivity in rainfed pasture systems.

Soil emissions of greenhouse gas nitrous oxide (N₂O) were measured in a series of field trials in a vegetable production system in temperate Australia. Approximately 4-fold higher N₂O emissions were observed from the use of poultry manure when compared with those obtained from using inorganic fertilisers. Nitrification inhibitors were able to reduce N₂O emissions and are a promising mitigation option, especially when used with poultry manure.

Enhanced efficiency fertilisers (EEFs) are promoted as a potential strategy to mitigate N₂O emissions and improve crop nitrogen use efficiency (NUE). We examined the effect of three different EEFs on N₂O emissions, NUE and yield in a cereal cropping system. Two EEFs were highly effective, decreasing annual N₂O losses by 83% and 70%, respectively, however, did not affect the yield or NUE. Further research is needed to assess if the increased costs of EEFs can be compensated by lower fertiliser application rates.

The grain yield responses of sorghum to rates of fertiliser N applied as urea or urea coated with the nitrification inhibitor DMPP were compared on a Vertisol and an Oxisol. DMPP had a similar impact at both sites, inhibiting nitrification for up to 8 weeks and reducing seasonal N₂O emissions by 60% when compared with conventional urea. Lower N₂O emissions observed with DMPP did not translate into significant yield gains or improvements in agronomic efficiencies of fertiliser N use.

DMPP-treated urea resulted in only slight increases in grain yield when compared with untreated urea. Agronomic efficiency was ≈2.2 kg grain/kg fertiliser higher. The use of DMPP treatment is suggested for scenarios with application rates >80 kg/ha.

The efficacy of polymer-coated or nitrification inhibitor-coated urea for reducing nitrous oxide emissions and improving fertiliser nitrogen efficiency was assessed in a sugarcane crop in the wet tropics of Australia. Application of the coated urea did not significantly affect the nitrous oxide emissions, but the crop nitrogen uptake was maintained at about 70% of the recommended application rate of conventional urea. The results demonstrated that fertiliser nitrogen inputs in sugarcane farms can be decreased using the coated urea, potentially reducing fertiliser nitrogen loss into the environment.

The farming practice of pasture termination greatly affected the N₂O emissions in the two-year field study conducted, influencing accumulation of NO₃-N during fallow period after termination. Late pasture termination reduced emissions by nearly 90% in the first year of the study. Soil water content was a key factor, limiting the magnitude of N₂O emissions with most annual emissions occurring when the water-filled pore space was above 65%. The late pasture termination can be used as an effective method for reducing N₂O emissions in regional agricultural soils.

A meta-analysis of nitrous oxide (N₂O) emissions from Vertosols under cotton in Australia found a two-component (linear + exponential) statistical model was preferred when describing emissions factors of N₂O emissions in response to nitrogen fertiliser additions of up to 300 kg N ha^–1

Increasing nitrogen (N) fertiliser rates for annual crops may increase N₂O emissions linearly, exponentially or not at all. Trials with grain sorghum (Sorghum bicolor L.) or sunflower (Helianthus annuus L.) in sub-tropical Vertosols showed a linear increase in N₂O with increasing N rate, but the rate of N₂O loss was five times greater in wetter-than-average seasons than in drier conditions.

Identifying strategies to reduce greenhouse gas emissions from cropping soils is important for decreasing the Grains Industry’s contribution to the detrimental effects of global warming. Cropping soils in south-west Victoria can become waterlogged and produce large amounts of nitrous oxide, a potent greenhouse gas. However, supplying the right amount of nitrogen fertiliser at peak crop demand will substantially reduce emissions without compromising yield. Through improved nitrogen fertiliser management, grain growers in south-west Victoria can reduce emissions while maintaining crop yields.

We measured soil N₂O and CH₄ fluxes associated with N-fertilised wheat and barley production on subtropical Vertosol soils. Intensive rainfall before and after sowing enhanced N-fertiliser treatment differences in N₂O flux but did not affect CH₄ flux. Both split N application and nitrification inhibitor coating on urea at sowing reduced N₂O flux. Dry conditions after sowing reduced the overall impact of N fertiliser on N₂O flux but increased soil CH₄ uptake.

Agricultural production can release significant amounts of nitrous oxide, a powerful greenhouse gas, to the atmosphere.  In irrigated systems, it is unclear if significant amounts of nitrous oxide are emitted from water storages or canals. In general, the irrigation system contributes 2.4–4% of the total nitrous oxide emission.

This study addressed the mitigation of N₂O emissions from grain cropping systems across eastern Australia using the APSIM model, following its evaluation at six diverse field sites covering major grain-growing regions in eastern Australia. We found that N management strategies that maximise yields and increase N use efficiency showed the greatest promise for N₂O mitigation. Splitting N fertiliser application in the southern grain-growing region and growing grain legumes in rotation with cereal crops had potential to reduce emissions.

Pastures used for dairying rely on substantial inputs of nitrogen (N), and N use efficiency (NUE) is often low. The ability of nitrification and urease inhibitors to reduce N losses and increase pasture yields and NUE was assessed. There was no treatment effect (P > 0.05) on soil mineral N, pasture yield, nitrous oxide flux or leaching of nitrate when compared with the use of standard urea. Further research is required to determine if and under what conditions inhibitor products can improve NUE.