Arvin R. Mosier

N2O emissions from agricultural lands: a synthesis of simulation approaches

Nitrous oxide (N2O) is primarily produced by the microbially-mediated nitrification and denitrification processes in soils. It is influenced by a suite of climate (i.e. temperature and rainfall) and soil (physical and chemical) variables, interacting soil and plant nitrogen (N) transformations (either competing or supplying substrates) as well as land management practices. It is not surprising that N2O emissions are highly variable both spatially and temporally. Computer simulation models, which can integrate all of these variables, are required for the complex task of providing quantitative determinations of N2O emissions. Numerous simulation models have been developed to predict N2O production. Each model has its own philosophy in constructing simulation components as well as performance strengths. The models range from those that attempt to comprehensively simulate all soil processes to more empirical approaches requiring minimal input data. These N2O simulation models can be classified into three categories: laboratory, field and regional/global levels. Process-based field-scale N2O simulation models, which simulate whole agroecosystems and can be used to develop N2O mitigation measures, are the most widely used. The current challenge is how to scale up the relatively more robust field-scale model to catchment, regional and national scales. This paper reviews the development history, main construction components, strengths, limitations and applications of N2O emissions models, which have been published in the literature. The three scale levels are considered and the current knowledge gaps and challenges in modelling N2O emissions from soils are discussed.

The potential for carbon sequestration in Australian agricultural soils is technically and economically limited

Concerns about increasing concentrations of greenhouse gases in the atmosphere, primarily carbon dioxide (CO2), have raised worldwide interest in the potential of agricultural soils to be carbon (C) sinks. In Australia, studies that have quantified the effects of improved management practices in croplands on soil C have generally been inconclusive and contradictory for different soil depths and durations of the management changes. We therefore quantitatively synthesised the results of Australian studies using meta-analytic techniques to assess the technical and economic feasibility of increasing the soil C stock by improved management practices. Our results indicate that the potential of these improved practices to store C is limited to the surface 0–10 cm of soil and diminishes with time. None of these widely adopted practices is currently financially attractive under Australias new legislation known as the Carbon Farming Initiative.

Effects of lignite application on ammonia and nitrous oxide emissions from cattle pens

Beef cattle feedlots are a major source of ammonia (NH3) emissions from livestock industries. We investigated the effects of lignite surface applications on NH3 and nitrous oxide (N2O) emissions from beef cattle feedlot pens. Two rates of lignite, 3 and 6kgm(-2), were tested in the treatment pen. No lignite was applied in the control pen. Twenty-four Black Angus steers were fed identical commercial rations in each pen. We measured NH3 and N2O concentrations continuously from 4th Sep to 13th Nov 2014 using Quantum Cascade Laser (QCL) NH3 analysers and a closed-path Fourier Transform Infrared Spectroscopy analyser (CP-FTIR) in conjunction with the integrated horizontal flux method to calculate NH3 and N2O fluxes. During the feeding period, 16 and 26% of the excreted nitrogen (N) (240gNhead(-1)day(-1)) was lost via NH3 volatilization from the control pen, while lignite application decreased NH3 volatilization to 12 and 18% of the excreted N, for Phase 1 and Phase 2, respectively. Compared to the control pen, lignite application decreased NH3 emissions by approximately 30%. Nitrous oxide emissions from the cattle pens were small, 0.10 and 0.14gN2O-Nhead(-1)day(-1) (<0.1% of excreted N) for the control pen, for Phase 1 and Phase 2, respectively. Lignite application increased direct N2O emissions by 40 and 57%, to 0.14 and 0.22gN2O-Nhead(-1)day(-1), for Phase 1 and Phase 2, respectively. The increase in N2O emissions resulting from lignite application was counteracted by the lower indirect N2O emission due to decreased NH3 volatilization. Using 1% as a default emission factor of deposited NH3 for indirect N2O emissions, the application of lignite decreased total N2O emissions.

Influence of elevated atmospheric carbon dioxide and supplementary irrigation on greenhouse gas emissions from a spring wheat crop in southern Australia

The effect of elevated carbon dioxide (CO 2 ) concentration on greenhouse gas (GHG) emission from semi-arid cropping systems is poorly understood. Closed static chambers were used to measure the fluxes of nitrous oxide (N 2 O), CO 2 and methane (CH 4 ) from a spring wheat ( Triticum aestivum L. cv. Yitpi) crop-soil system at the Australian grains free-air carbon dioxide enrichment (AGFACE) facility at Horsham in southern Australia in 2009. The targeted atmospheric CO 2 concentrations (hereafter CO 2 concentration is abbreviated as [CO 2 ]) were 390 (ambient) and 550 (elevated) μmol/mol for both rainfed and supplementary irrigated treatments. Gas measurements were conducted at five key growth stages of wheat. Elevated [CO 2 ] increased the emission of N 2 O and CO 2 by 108 and 29%, respectively, with changes being greater during the wheat vegetative stage. Supplementary irrigation reduced N 2 O emission by 36%, suggesting that N 2 O was reduced to N 2 in the denitrification process. Irrigation increased CO 2 flux by 26% at ambient [CO 2 ] but not at elevated [CO 2 ], and had no impact on CH 4 flux. The present results suggest that under future atmospheric [CO 2 ], agricultural GHG emissions at the vegetative stage may be higher and irrigation is likely to reduce the emissions from semi-arid cropping systems.

Using urease and nitrification inhibitors to decrease ammonia and nitrous oxide emissions and improve productivity in a subtropical pasture

Urease and nitrification inhibitors are designed to mitigate ammonia (NH3) volatilization and nitrous oxide (N2O) emission, but uncertainties on the agronomic and economic benefits of these inhibitors prevent their widespread adoption in pasture systems, particularly in subtropical regions where no such information is available. Here we report a field experiment that was conducted in a subtropical pasture in Queensland, Australia to examine whether the use of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT, applied as Green UreaNV®) and the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP, applied as Urea with ENTEC®) is environmentally, agronomically and economically viable. We found that Green UreaNV® and Urea with ENTEC® decreased NH3 volatilization and N2O emission by 44 and 15%, respectively, compared to granular urea. Pasture biomass and nitrogen (N) uptake were increased by 22-36% and 23-32%, respectively, with application of the inhibitors compared to granular urea. A simple economic assessment indicates that the fertilizer cost for pasture production was 5.4, 4.4 and 6.0 Australian cents per kg dry matter for urea, Green UreaNV® and Urea with ENTEC®, respectively, during the experimental period. The mitigation of N loss using the inhibitors can reduce the environmental cost associated with pasture production. These results suggest that the use of these inhibitors can provide environmental, agronomic and economic benefits to a subtropical pasture.