Reducing greenhouse gas emissions from agriculture

PhD projects associated with the Non-CO₂ Greenhouse Gas Program of the CRC for Greenhouse Accounting

(Program F: Non –CO₂ greenhouse gases, Program Leader Dr Rich Eckard)

Agricultural industries are responsible for 25-35% of Australia’s greenhouse gas emissions in the form of methane (CH₄) and nitrous oxide (N₂O). Current audits by the Australian Greenhouse Office suggest that N₂O may contribute about 17.5% of the total emissions from Australian agriculture. Nitrous oxide (N₂O) is a potent greenhouse gas, with global warming factor of 300 times that of CO₂, but the sources of these emissions are currently not well quantified, nor have management options been developed to reduce them. There are few credible measurements of emissions of N₂O from Australian farming systems to adequately account for the large temporal variability in emissions. The increasing use of nitrogenous fertilisers on intensive dairy pastures, and in horticulture and cropping systems has created the need for detailed research on emission measurement, predictive modelling, and potential management options to reduce emissions. A non-CO₂ Greenhouse Gas Program has been established within the CRC for Greenhouse Accounting to implement research on nitrous oxide and methane emissions from agriculture. The broad aims of this research are to support the development of non-CO₂ emissions accounting within the National Carbon Accounting System, to develop a spatially referenced model to predict greenhouse gas emissions at large scales, such as catchment scales, and to develop cost-effective, management practices and a decision support model to mitigate non-CO₂ greenhouse gases. Three PhD scholarships are available in the area of N₂O research. Each PhD project has a different focus, but all three are to be closely linked.

1. Quantifying relationships between soil properties and rate constants for nitrogen transformations in soils, with particular focus on denitrification and the ratio N₂O/N2 emitted during denitrification

   CRC Program F: Non –CO₂ greenhouse gases
   Project F1: Environmental and Management Drivers of Non –CO₂ greenhouse gases in Agro-ecosystems
   Contact: Dr Deli Chen (delichen@unimelb.edu.au) or Dr Robert Edis (roberte@unimelb.edu.au) or Professor Robert White (robertew@unimelb.edu.au)

   Almost 80% of N₂O emissions in Australia are from agricultural lands, originating from N fertilisers, animal waste and soil disturbance. Nitrous oxide is primarily produced in soil by the anaerobic activities of microorganisms during denitrification, although nitrification also contributes some N₂O emission in aerobic soils. Denitrification interacts closely with other nitrogen transformation processes in soil, which either provide the substrate nitrate (mineralisation and nitrification) or complete for nitrate and its precursor ammonium (ammonia volatilisation and immobilisation). It is necessary to understand and quantify the relevant N transformations in order to accurately predict the extent of denitrification and N₂O emission. The accurate prediction of rate constants of these key nitrogen transformations is essential to spatially modelling water, nutrient management, and greenhouse gas emission in agroecosystems. The N₂O flux largely depends on the ratio of N₂O/N₂ during denitrification, which is highly variable and influenced by a range of soil properties and environmental conditions.

   This Ph D project will attempt to develop quantitative relationships between intrinsic soil properties and the rate of key N transformations in soils. By means primarily of controlled laboratory experiments, rate constants for nitrogen transformations and the N₂O/N₂ ratios for nitrification/denitrification will be measured in the representative Australian soils. The results will be used to develop pedo-transfer functions describing quantitative relationships between intrinsic soil properties and N transformation rates. The outcomes of this project will provide valuable parameters for decision-support models to develop best management practices for minimum N₂O emissions from agricultural systems.

   The PhD candidate will develop expertise in soil chemical analysis and nutrient management, especially with respect to soil nitrogen transformations, and skills in statistical analysis of large data sets. The successful candidate must have good knowledge of soil science, particularly soil microbiology, soil biochemistry and quantitative methods. Competence in analytical chemistry will be an advantage.

 

2. Quantifying N₂O emissions from key agricultural systems using chambers and micrometeorological methods

   CRC Program F: Non –CO₂ greenhouse gases
   Project F1: Environmental and Management Drivers of Non –CO₂ greenhouse gases in Agro-ecosystems
   Contact: Dr Ray Leuning (ray.leuning@csiro.au) or Dr Deli Chen (delichen@unimelb.edu.au) or Dr Ian Galbally (Ian.Galbally@csiro.au)

   Very limited measurements of nitrous oxide emissions are available for Australian agricultural systems. There is high level of uncertainty about the non-CO₂ greenhouse gas emissions estimated by the Australia’s National Greenhouse Gas Inventory Committee (NGGIC) and the Intergovernmental Panel on Climate Change (IPCC), because these estimates are mainly based on extrapolations of laboratory and enclosure measurements to the field scale. Because of high spatial variation, it is difficult to measure representative or ‘average’ fluxes of N₂O emissions across a large field with intact soil core or chamber techniques, although these techniques are useful to examine the effect of different treatments or management practices. Micrometeorological flux measurements overcome this problem because they measures over a large paddock (>100 m radius) and integrate the spatial variation across the field.

   The PhD candidate will study the emissions of N₂O from major agricultural systems, especially irrigated pasture, as part of the CRC program using the advanced micrometeorological instrumentation provided by the Victorian Department of Primary Industries. The candidate will become expert in all technical and theoretical aspects of the micrometeorological measurements and their application to a key agricultural system. The candidate will also develop expertise in the use of chambers placed over the surface to measure N₂O emissions, and be able to compare methodologies.

   Because N₂O emissions result from the complex transformations of various forms of nitrogen in the soil by microorganisms and are influenced by many soil and environmental factors, a comprehensive process model is needed to predict emission rates under a range of environmental and soil conditions. The PhD project will utilize field data obtained during the study to test the N₂O emission sub-model of a spatially referenced water and nitrogen management model (WNMM). The model must contribute to identifying the best management practices (BMPs) for increasing nitrogen fertilizer efficiency and reducing N₂O emissions.

   The successful candidate must have a good grounding in physics, mathematics, chemical engineering, meteorology or agricultural chemistry. Knowledge of basic chemistry and the physics of energy and mass transfer in porous media and in the atmosphere will be an advantage. The candidate must have a strong interest in applying their skills to environmental problems.

 

3. Development of a spatially referenced model for identifying optimal strategies for managing water and fertilizer nitrogen to reduce N₂O emissions from key agricultural systems.

   CRC Program F: Non –CO₂ greenhouse gases
   Project F2: Farming Systems to Reduce Emissions
   Contact: Professor Bob White (robertew@unimelb.edu.au), Dr Deli Chen (delichen@unimelb.edu.au) or Richard Eckard (rjeckard@unimelb.edu.au)

   The processes of N₂O emission, nitrification and denitrification, are strongly influenced by the soil and environmental factors and management practices, which are spatially variable. An effective decision support model for reducing N₂O emissions for Australian agricultural systems has to be spatially referenced and catchment based. It is well known that a key factor controlling N₂O emissions is the soil water status. Therefore, it is essential for a model to have three-dimension capability to simulate water and solute movement in the landscape.

   The main aim of this Ph D project will be to incorporate a soil-plant process model describing water and N fluxes, including N₂O emissions, into a Geographical Information System (GIS), so that inputs, transformations and losses (in solution and in gaseous forms) can be spatially referenced to basic cadastral data, soil properties, land use and management practices. The project will involve (1) expanding the capability of a two-dimensional GIS based water and nitrogen model to allow three-dimensional simulation of water and solute movement over the landscape and in subsoils; (2) scaling up the parameters involved in bio-physical model simulations using geostatistics, remote sensing, and pedo-transfer functions; and (3) calibrating the model using field data obtained from chamber and micrometrological measurements of gas fluxes.

   This spatially referenced model will provide a base to develop a decision support model to identify best management practices (BMPs) for managing water and fertilizer nitrogen to reduce N₂O emissions from key agricultural systems. The PhD candidate will be trained to be the expert in water and nutrient modelling, spatially spatial modelling. The candidate must have good knowledge and ability in computer modelling and GIS software. Knowledge of basic soil science, hydrology and solute transfer in porous media will be an advantage.

Applications close on 4 August 2003.