Volume 54 Number 5 2016
Nitrous Oxides in Soils
SR15304Nitrification rates and associated nitrous oxide emissions from agricultural soils – a synopsis
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.
SR15315Mitigation of N2O emissions from surface-irrigated cropping systems using water management and the nitrification inhibitor DMPP
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.
SR14328Non-linear response of soil N2O emissions to nitrogen fertiliser in a cotton–fallow rotation in sub-tropical Australia
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.
SR15289Tillage does not increase nitrous oxide emissions under dryland canola (Brassica napus L.) in a semiarid environment of south-eastern Australia
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.
SR15317Influence of enhanced efficiency fertilisation techniques on nitrous oxide emissions and productivity response from urea in a temperate Australian ryegrass pasture
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.
SR15320Mitigation of nitrous oxide emissions with nitrification inhibitors in temperate vegetable cropping in southern Australia
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.
SR15332Effect of enhanced efficiency fertilisers on nitrous oxide emissions in a sub-tropical cereal cropping system
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.
SR15336Comparison of grain yields and N2O emissions on Oxisol and Vertisol soils in response to fertiliser N applied as urea or urea coated with the nitrification inhibitor 3,4-dimethylpyrazole phosphate
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.
SR15337Agronomic responses of grain sorghum to DMPP-treated urea on contrasting soil types in north-eastern Australia
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.
SR15314Nitrous oxide emission and fertiliser nitrogen efficiency in a tropical sugarcane cropping system applied with different formulations of urea
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.
SR15307Use of the agricultural practice of pasture termination in reducing soil N2O emissions in high-rainfall cropping systems of south-eastern Australia
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.
SR16091Emission factors for estimating fertiliser-induced nitrous oxide emissions from clay soils in Australia’s irrigated cotton industry
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
SR15286The interaction of seasonal rainfall and nitrogen fertiliser rate on soil N2O emission, total N loss and crop yield of dryland sorghum and sunflower grown on sub-tropical Vertosols
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.
SR15292Effect of nitrogen fertiliser management on soil mineral nitrogen, nitrous oxide losses, yield and nitrogen uptake of wheat growing in waterlogging-prone soils of south-eastern Australia
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.
SR15338Greenhouse gas (N2O and CH4) fluxes under nitrogen-fertilised dryland wheat and barley on subtropical Vertosols: risk, rainfall and alternatives
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.
SR15376Nitrous oxide emissions from grain production systems across a wide range of environmental conditions in eastern Australia
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.
SR15330Nitrification (DMPP) and urease (NBPT) inhibitors had no effect on pasture yield, nitrous oxide emissions, or nitrate leaching under irrigation in a hot-dry climate
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.