Research highlights
Measuring nitrous oxide emissions from dairy pasture
Improving global understanding of soil carbon dynamics
Organic soil carbon is a dynamic ecosystem. Each year, soil respiration sends about 10 times more carbon into the atmosphere than that from burning fossil fuels. For soils in carbon–balance, losses from soil respiration are balanced by inputs from vegetation. This has important consequences for the regulation of atmospheric carbon dioxide (CO2) and thus the rate of global warming.
Various global climate models generally agree that warming is expected to lead to a loss of soil organic carbon, while increasing CO2 is expected to stimulate plant net primary productivity and increase carbon stocks. However, predictions of the combined effect of both increased CO2 and climate change on carbon stocks vary between models.
Our research indicates that for global applications, consideration of seasonal temperature variations is critical. Short–term measures of temperature dependence cannot be applied at different temporal scales without explicitly considering the variability of temperature over the longer temporal scale. Using short time–steps in simulations results in more positive changes in soil carbon (sequestration), especially in cold regions, than would be predicted in simulations at the more commonly used annual time–steps that ignore seasonal temperature variations. These results help to reconcile some of the apparent differences in predictions obtained by different models.
Measuring soil respiration in situ
As a means of detecting changes over time, direct measurement of soil organic matter is very insensitive. Methods that facilitate a more detailed understanding and quantification of the biological processes underlying soil carbon balance hold much greater potential to help understand how soils respond to extraneous influences.
With our tunable diode laser, we can now measure very small differences in the isotopic carbon signature of CO2. This helps us distinguish between old carbon (in soil organic matter) and recently fixed carbon (in plant tissue) as soil respiration sources, without disturbing the ecosystem. We found that the proportion of old to new carbon used in respiration is markedly influenced by soil fertility. In a low–fertility soil with actively growing plants, more than 80% of the total soil respiration originated from newly fixed carbon. As temperature increased, the respiration rate also increased but loss of old carbon did not increase as expected. In contrast, an increase in temperature of a high–fertility soil increased both the rate of respiration and the proportion originating from old carbon sources. Results suggest that warming of fertile soils increases the loss of the older stored carbon but in less fertile soils the increased respiration is mainly derived from recently fixed carbon.
Visualising carbon stored in New Zealand´s forests
Projections of expected changes in the amount of carbon stored in our forests are required for New Zealand’s ongoing climate change negotiations. This year, we led a project with Scion to produce a ‘first–edition layer’ of mean annual growth rates (carbon storage) of exotic forest for all of New Zealand. The mean annual growth of Pinus radiata over 50 years was mapped using regional estimates published by the Ministry of Agriculture and Forestry (MAF) in their Guide to Look–up Tables for the Emission Trading Scheme. The map will enable users to visualise trends in carbon sequestration following afforestation in some areas of the country. Future work will refine the map using forest growth estimates from current modelling work. While detailed empirical data and models exist for exotic production forests, the information for indigenous forests is much less clear. One of our new research projects for MAF will quantify carbon currently stored in native vegetation, the rate at which carbon accumulates at present (’business as usual’), and how ‘management’ options could optimise carbon sequestration in native forests.
Managing–to–mitigate nitrous oxide emissions
Nitrous oxide (N2O) comes principally from on–farm animal urine and fertiliser use, and is around 200 times more potent than CO2 in its global warming potential. Intensification in dairying and increased production of farm dairy effluent has raised concerns about gaseous nitrogen losses and their environmental implications. Recent FRST–funded research showed that the rate of N2O emissions from dairy–grazed pasture increases after effluent is applied to the pasture. However, a longer delay between grazing and effluent irrigation reduces the amount of surplus nitrogen and labile carbon, and hence N2O emissions. Combined with other effluent irrigation studies, these results also suggest that application of effl uent in dry summer and autumn seasons would result in fewer N2O emissions than application at other times of the year.
Developing novel methane mitigation technologies
Methane (CH4) has 25 times the global warming potential of CO2, and accounts for over 40% of all New Zealand’s greenhouse gas emissions.
Our research has shown that soil can be a significant CH4 ‘sink’, and we are demonstrating the potential to use New Zealand soils in new mitigation technologies. Following the success of our prototype filter to reduce CH4 emitted (down by 60%) from a dairy effluent pond, we have begun designing similar biofilters to oxidise CH4 emissions from landfi lls. Emissions from currently operating landfills that do not have gas collection and management systems in place could be worth $28m per year in reducing emissions liabilities. In addition, about 250 landfi lls closed after 1995 but will continue to emit greenhouse gases for over 30 years. Waste sector emissions will come into the Emissions Trading Scheme in 2011, so this technology will help landfill operators (largely local bodies) reduce liabilities resulting from greenhouse gas emissions from landfills. The project has support from MAF, with collaboration from Taupo District Council and the School of Engineering and Advanced Technology, Massey University.
Linking with the global research alliance
Following the inaugural meeting of the new Global Research Alliance on Agricultural Greenhouse Gas Research in Wellington this year, senior officials and delegates visited the new Agricultural Greenhouse Gas Research Centre, in which we are a partner, at Palmerston North. The visit included Landcare Research’s laboratory and field experiments on N2O emissions from pastures and the potential for CH4 oxidisers in waste treatment. Lively discussions ranged across mitigation of enteric emissions, measurement techniques and spatial–temporal variability in N2O emissions, the potential for mitigation technologies and their level of uptake in New Zealand, and new approaches to mitigation. Contacts made during the visit – particularly between New Zealand and The Netherlands, who will jointly coordinate a livestock research group – will facilitate collaborative projects to mitigate global agricultural greenhouse emissions.
Managing Climate Change (MC2) conference
This year, we were the principal organiser of the 2–day conference ’Managing Climate Change (MC2)’. This brought together about 130 representatives from 14 countries to share the latest data and information on the processes that generate greenhouse gases, and technologies to measure, model and mitigate emissions. The conference facilitated the exchange of information and ideas between widely dispersed groups involved in managing greenhouse gas emissions. It also aimed to remove barriers between policy, science and industry and to foster dialogue among researchers, academics, students, environmentalists, engineers, land managers, and officials of industry and government.
MC2was organised in cooperation with AGMARDT, AgResearch, AGROTAIN International, Ballance Agri–Nutrients, the Global DNDC Network, GNS, the Livestock Emissions Abatement Research Network (LEARN), Massey University, MAF Policy, NIWA, PGgRC, Ravensdown Fertilisers, Summit–Quinphos (NZ) and Quinspread Technologies.