@article{Schwenke2016,
title = {The interaction of seasonal rainfall and nitrogen fertiliser rate on soil N_{2}O emission, total N loss and crop yield of dryland sorghum and sunflower grown on sub-tropical Vertosols},
author = {G. D. Schwenke and B. M. Haigh},
doi = {10.1071/SR15286},
year = {2016},
date = {2016-06-27},
journal = {Soil Research},
volume = {54},
number = {5},
pages = {604-618},
abstract = {Summer crop production on slow-draining Vertosols in a sub-tropical climate has the potential for large emissions of soil nitrous oxide (N_{2}O) from denitrification of applied nitrogen (N) fertiliser. While it is well established that applying N fertiliser will increase N_{2}O emissions above background levels, previous research in temperate climates has shown that increasing N fertiliser rates can increase N_{2}O emissions linearly, exponentially or not at all. Little such data exists for summer cropping in sub-tropical regions. In four field experiments at two locations across two summers, we assessed the impact of increasing N fertiliser rate on both soil N_{2}O emissions and crop yield of grain sorghum (\textit{Sorghum bicolor} L.) or sunflower (\textit{Helianthus annuus} L.) in Vertosols of sub-tropical Australia. Rates of N fertiliser, applied as urea at sowing, included a nil application, an optimum N rate and a double-optimum rate.

Daily N_{2}O fluxes ranged from –3.8 to 2734 g N_{2}O-N ha^{–1} day^{–1} and cumulative N_{2}O emissions ranged from 96 to 6659 g N_{2}O-N ha^{–1} during crop growth. Emissions of N_{2}O increased with increased N fertiliser rates at all experimental sites, but the rate of N loss was five times greater in wetter-than-average seasons than in drier conditions. For two of the four experiments, periods of intense rainfall resulted in N_{2}O emission factors (EF, percent of applied N emitted) in the range of 1.2–3.2%. In contrast, the EFs for the two drier experiments were 0.41–0.56% with no effect of N fertiliser rate.
Additional ^{15}N mini-plots aimed to determine whether N fertiliser rate affected total N lost from the soil–plant system between sowing and harvest. Total ^{15}N unaccounted was in the range of 28–45% of applied N and was presumed to be emitted as N_{2}O + N_{2}. At the drier site, the ratio of N_{2} (estimated by difference) to N_{2}O (measured) lost was a constant 43%, whereas the ratio declined from 29% to 12% with increased N fertiliser rate for the wetter experiment.
Choosing an N fertiliser rate aimed at optimum crop production mitigates potentially high environmental (N_{2}O) and agronomic (N_{2} + N_{2}O) gaseous N losses from over-application, particularly in seasons with high intensity rainfall occurring soon after fertiliser application.},
keywords = {Soil Research 54},
pubstate = {published},
tppubtype = {article}
}

@article{Farquharson2016,
title = {Nitrification rates and associated nitrous oxide emissions from agricultural soils – a synopsis},
author = {Ryan Farquharson},
doi = {10.1071/SR15304},
year = {2016},
date = {2016-06-27},
journal = {Soil Research},
volume = {54},
number = {5},
pages = {469-480},
abstract = {Laboratory incubations were performed to estimate nitrification rates and the associated nitrous oxide (N_{2}O) emissions under aerobic conditions on a range of soils from National Agricultural Nitrous Oxide Research Program field sites. Significant site-to-site variability in nitrification rates and associated N_{2}O emissions was observed under standardised conditions, indicating the need for site-specific model parameterisation. Generally, nitrification rates and N_{2}O emissions increased with higher water content, ammonium concentration and temperature, although there were exceptions. It is recommended that site-specific model parameterisation be informed by such data. Importantly, the ratio of N_{2}O emitted to net nitrified N under aerobic conditions was small (<0.2% for the majority of measurements) but did vary from 0.03% to 1%. Some models now include variation in the proportion of nitrified N emitted as N_{2}O as a function of water content; however, strong support for this was not found across all of our experiments, and the results demonstrate a potential role of pH and ammonium availability. Further research into fluctuating oxygen availability and the coupling of biotic and abiotic processes will be required to progress the process understanding of N_{2}O emissions from nitrification.},
keywords = {Soil Research 54},
pubstate = {published},
tppubtype = {article}
}

@article{Li2016,
title = {Tillage does not increase nitrous oxide emissions under dryland canola (Brassica napus L.) in a semiarid environment of south-eastern Australia},
author = {Guangdi D. Li and Mark K. Conyers and G. D. Schwenke and Richard C. Hayes and De Li Liu and Adam J. Lowrie and Graeme J. Poile and Albert A. Oates and Richard J. Lowrie},
doi = {10.1071/SR15289},
year = {2016},
date = {2016-06-21},
journal = {Soil Research},
volume = {54},
number = {5},
pages = {512-522},
abstract = {Dryland cereal production systems of south-eastern Australia require viable options for reducing nitrous oxide (N_{2}O) emissions without compromising productivity and profitability. A 4-year rotational experiment with wheat (\textit{Triticum aestivum} L.)–canola (\textit{Brassica napus} L.)–grain legumes–wheat in sequence was established at Wagga Wagga, NSW, Australia, in a semiarid Mediterranean-type environment where long-term average annual rainfall is 541 mm and the incidence of summer rainfall is episodic and unreliable. The objectives of the experiment were to investigate whether (i) tillage increases N_{2}O emissions and (ii) nitrogen (N) application can improve productivity without increasing N_{2}O emissions. The base experimental design for each crop phase was a split-plot design with tillage treatment (tilled versus no-till) as the whole plot, and N fertiliser rate (0, 25, 50 and 100 kg N/ha) as the subplot, replicated three times. This paper reports high resolution N_{2}O emission data under a canola crop. The daily N_{2}O emission rate averaged 0.55 g N_{2}O-N/ha.day, ranging between –0.81 and 6.71 g N_{2}O-N/ha.day. The annual cumulative N_{2}O-N emitted was 175.6 and 224.3 g N_{2}O-N/ha under 0 and 100 kg N/ha treatments respectively. There was no evidence to support the first hypothesis that tillage increases N_{2}O emissions, a result which may give farmers more confidence to use tillage strategically to manage weeds and diseases where necessary. However, increasing N fertiliser rate tended to increase N_{2}O emissions, but did not increase crop production at this site.},
keywords = {Soil Research 54},
pubstate = {published},
tppubtype = {article}
}

@article{Schwenke2016b,
title = {Greenhouse gas (N_{2}O and CH_{4}) fluxes under nitrogen-fertilised dryland wheat and barley on subtropical Vertosols: risk, rainfall and alternatives},
author = {G. D. Schwenke and David F. Herridge and Clemens Scheer and David W. Rowlings and Bruce M. Haigh and K. Guy McMullen},
doi = {10.1071/SR15338},
year = {2016},
date = {2016-06-21},
journal = {Soil Research},
volume = {54},
number = {5},
pages = {634-650},
abstract = {The northern Australian grains industry relies on nitrogen (N) fertiliser to optimise yield and protein, but N fertiliser can increase soil fluxes of nitrous oxide (N_{2}O) and methane (CH_{4}). We measured soil N_{2}O and CH_{4} fluxes associated with wheat (\textit{Triticum aestivum}) and barley (\textit{Hordeum vulgare}) using automated (Expts 1, 3) and manual chambers (Expts 2, 4, 5). Experiments were conducted on subtropical Vertosol soils fertilised with N rates of 0–160 kg N ha^{–1}.
In Expt 1 (2010), intense rainfall for a month before and after sowing elevated N_{2}O emissions from N-fertilised (80 kg N ha^{–1}) wheat, with 417 g N_{2}O-N ha^{–1} emitted compared with 80 g N_{2}O-N ha^{–1} for non-fertilised wheat. Once crop N uptake reduced soil mineral N, there was no further treatment difference in N_{2}O. Expt 2 (2010) showed similar results, however, the reduced sampling frequency using manual chambers gave a lower cumulative N_{2}O. By contrast, very low rainfall before and for several months after sowing Expt 3 (2011) resulted in no difference in N_{2}O emissions between N-fertilised and non-fertilised barley. N_{2}O emission factors were 0.42, 0.20 and –0.02 for Expts 1, 2 and 3, respectively. In Expts 4 and 5 (2011), N_{2}O emissions increased with increasing rate of N fertiliser. Emissions were reduced by 45% when the N fertiliser was applied in a 50 : 50 split between sowing and mid-tillering, or by 70% when urea was applied with the nitrification inhibitor 3,4-dimethylpyrazole-phosphate.
Methane fluxes were typically small and mostly negative in all experiments, especially in dry soils. Cumulative CH_{4} uptake ranged from 242 to 435 g CH_{4}-C ha^{–1} year^{–1}, with no effect of N fertiliser treatment. Considered in terms of CO_{2} equivalents, soil CH_{4} uptake offset 8–56% of soil N_{2}O emissions, with larger offsets occurring in non-N-fertilised soils.
The first few months from N fertiliser application to the period of rapid crop N uptake pose the main risk for N_{2}O losses from rainfed cereal cropping on subtropical Vertosols, but the realisation of this risk is dependent on rainfall. Strategies that reduce the soil mineral N pool during this time can reduce the risk of N_{2}O loss.},
keywords = {Soil Research 54},
pubstate = {published},
tppubtype = {article}
}

@article{Jamali2016,
title = {Mitigation of N_{2}O emissions from surface-irrigated cropping systems using water management and the nitrification inhibitor DMPP},
author = {Hizbullah Jamali and Wendy Quayle and Clemens Scheer and Jeff Baldock},
doi = {10.1071/SR15315},
year = {2016},
date = {2016-03-11},
journal = {Soil Research},
volume = {54},
number = {5},
pages = {481-493},
abstract = {Soils under irrigated agriculture are a significant source of nitrous oxide (N_{2}O) owing to high inputs of nitrogen (N) fertiliser and water. This study investigated the potential for N_{2}O mitigation by manipulating the soil moisture deficit through irrigation scheduling in combination with, and in comparison to, using the nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP). Lysimeter cores planted with wheat were fitted with automated chambers for continuous measurements of N_{2}O fluxes. Treatments included conventional irrigation (CONV), reduced deficit irrigation (RED), CONV-DMPP and RED-DMPP. The total seasonal volume of irrigation water applied was constant for all treatments but the timing and quantity in individual irrigation applications varied among treatments. ^{15}N-labelled urea was used to track the source of N_{2}O emissions and plant N uptake. The majority of N_{2}O emissions occurred immediately after irrigations began on 1 September 2014. Applying RED and DMPP individually slightly decreased N_{2}O emissions but when applied in combination (RED-DMPP) the greatest reductions in N_{2}O emissions were observed. There was no effect of treatments on plant N uptake, ^{15}N recovery or yield possibly because the system was not N limited. Half of the plant N and 53% to 87% of N_{2}O was derived from non-fertiliser sources in soil, highlighting the opportunity to further exploit this valuable N pool.},
keywords = {Soil Research 54},
pubstate = {published},
tppubtype = {article}
}