Impact 2 - Management
Native trees growing up through flowering gorse. Most of the land in this picture would qualify as ‘forest’. Image - Larry Burrows
Land-use options, asset management and other methods that increase carbon storage and mitigate greenhouse gas emissions are understood and balanced for environmental, economic and social benefits.
Impacts of land use change on greenhouse gas inventories
Land use change between forestry and agriculture can generate high levels of net carbon dioxide (CO2) emissions, which obviously has important implications for New Zealand’s long-term greenhouse gas inventories and economic liabilities. Reforestation of pastoral land can regain former carbon stocks, but the rate of carbon sequestration is much slower than the rate of carbon loss from deforestation.
Recent research also found that nitrous oxide (N2O) and methane (CH4) emissions from grazed pastures and ruminant livestock are much higher than from forests. However because of the shorter atmospheric ‘lifespan’ of CH4, emissions from converted pasture accumulate for only a few decades before concentrations reach a new equilibrium.
N2O has much greater longevity in the atmosphere −concentrations accumulate nearly linearly for many decades. This means the true impact of converting forestry to pastoral agriculture will continue far into the future.
But pastoral grassland soils in New Zealand could become a greater carbon sink. Our analysis of 10 years’ research data on the impact of elevated atmospheric CO2 concentrations clearly show that even when atmospheric CO2 concentrations reach 475 ppm (perhaps in 30 years), CO2 fertilisation will have very significant effects on some key soil properties, including soil carbon and nitrogen levels. Such increases in soil carbon indicate a potential to mitigate carbon emissions.
Policymakers, when using this new information in combination with climate warming data, will be better able to anticipate changes needed in future pasture management across different parts of New Zealand.
This research is part of the Measuring Greenhouse Gases and Carbon Storage portfolio, and was supported by Core funding.
Continuous, in-situ, measurements of agricultural greenhouse gases
We have established a long-term research site on a newly converted, irrigated dairy farm (Synlait’s Beacon Farm) on the mid-Canterbury plains. We installed automated systems to continuously measure concentrations of CO2, CH4 and N2O at identical irrigated and un-irrigated pasture sites, providing a time series of the fluxes of all three greenhouse gases. We also take continuous measurements of environmental variables that control greenhouse gas exchange, including pasture height, soil temperature, soil moisture and irrigation events. Pasture production and the amount of carbon removed by grazing are being quantified. As all these measurements continue, they will build our understanding and will allow us and Synlait to assess the effects of management changes and climate on the annual greenhouse gas budgets of an intensely managed dairy farm. Initial measurements have highlighted that after each grazing event, the pasture is a net source of CO2 for about 7 days, and becomes a progressively stronger sink during the next 2 weeks before the next grazing event.
We are collaborating with Lincoln University and the University of Canterbury to enable two studies of small-scale soil processes driving greenhouse gas fluxes. These projects, at Beacon Farm, are focusing on the conditions controlling N2O production and on relationships between above- and belowground CO2 fluxes.
This research is part of the Measuring Greenhouse Gases and Carbon Storage portfolio, and is supported by Core funding with considerable in-kind support from Synlait Farms Ltd.
Urease inhibitors
Ammonia (NH3) is a precursor to the formation of N2O. In research for Ballance Agri-Nutrients, we found that applying the urease inhibitor Agrotain® with urea fertiliser or applying irrigation (or rainfall) could significantly reduce NH3 emissions and improve fertiliser N-use efficiency in grazed pastoral systems. This enabled us to adjust and recommend values for NH3 emission factors for pastoral soils fertilised with Agrotain® treated urea. These recommendations have been adopted.
This research is part of the Measuring Greenhouse Gases and Carbon Storage portfolio, and was supported by Ballance Agri-Nutrients.
Methane biofiltration technology
We developed a biofilter capable of removing most of the methane (CH4) produced from dairy farm effluent ponds. Active CH4-eating bacteria (methanotrophs) in the biofilter convert the CH4 into biomass and some CO2; NH3 is also consumed. Earlier research identified a volcanic soil that contained a very active population of methanotrophs. In vitro experiments showed that a biofilter made from this soil could potentially remove almost all of the CH4 from an average dairy farm waste pond. Our first prototype CH4 biofilter has been consuming >95% of the CH4 in biogas from under a cover on an effluent pond at Massey University No. 4 dairy farm for about 3 years with minimal maintenance. We recently developed and successfully lab-tested a second biofilter, similar in efficiency to the first prototype, that will now be tested as part of a floating pond cover on a commercial dairy farm.
Interest in our CH4 biofilter has been shown by the UK and Spain, particularly for removing CH4 and NH3 emissions from livestock waste in a range of agricultural systems and regions.
This research is part of the Realising Land’s Potential portfolio, and was supported by Core funding and MPI funding.
Mapping gorse and broom as ‘forest’
Both MfE and MPI need to know how much of New Zealand’s vegetation qualifies as either pre1990 or post1989 ‘forest land’. Gorse and broom form a nurse canopy for indigenous trees that qualify as ‘forest trees’. In places where the succession is allowed to proceed to tall forest, the land is deemed forest land when there is a sufficient density of tree species that can reach 5m height at maturity with crown cover of at least 30% of each hectare. Because direct detection of trees is problematic, especially if they are underneath a gorse or broom canopy, we used national scale indirect measures of likelihood that a given area of gorse or broom will become forest and the average length of time this takes. This research will be used by MPI to determine whether applicants to the Emissions Trading Scheme (ETS) or Permanent Forest Sink Initiative (PFSI) have eligible forest land (or whether they have a deforestation liability). It also will be used to inform the development of new ETS lookup tables that take into account the initial lag phase between establishment of woody shrubs and establishment of tall forest.
This research is part of both the Managing Biodiversity Change and Measuring Greenhouse Gases and Carbon Storage portfolios, and was supported by MPI funding.
Carbon farming on Māori land
Māori land has been widely touted as being suitable for carbon sequestration, which led to strong interest from iwi in potential carbon farming enterprise. We investigated the extent and nature of Māori land resources at a national scale to gain broad understanding of land types, land capability, total carbon stocks and the potential for carbon sequestration. Results show there is considerably less Māori freehold land available for carbon sequestration under ‘Kyoto forest’ criteria. Instead of the one million hectares as previously talked about, only 482 000 ha meet Kyoto forest eligibility criteria; of this land, only 122 800 ha fit the definition of ‘undeveloped’. This undeveloped marginal land should be targeted by more effective policy and programmes, conducive to Māori aspirations and values, to promote forestry and protective vegetative cover on this fragile erosion-prone land.
Carbon sequestration remains a real opportunity on Māori land if schemes are aligned with Māori aspirations rather than Government and international agendas.
This research is part of both the Characterising Land’s Resources and Measuring Greenhouse Gases and Carbon Storage portfolios, and supported by Core funding, MBIE contestable funding and MPI funding.
Soil respiration and carbon sinks under tussock grasslands
Soil respiration plays a critical role in the regulation of carbon cycling at ecosystem and global scales, and is approximately 10-times our current anthropogenic carbon dioxide (CO2) emissions. The response of soil to rising temperatures is still currently debated, with some models suggesting that soils will become a net source rather than a sink of CO2. Other models suggest that an increased carbon sink in the soil, due to rising temperature, will offset the effects of increased CO2.
Understanding the processes regulating the temperature response of soil respiration is complex because there are two distinct components to soil respiration. First, respiration of roots and associated microbes causes rapid turnover of carbon in the system. Second, decomposition of soil organic matter and litter represents slower turnover of much larger carbon pools. Current models of carbon cycling assume both components behave the same way as the soil warms but the models would be affected profoundly by small variations in the rate of soil organic matter turnover between the two components.
Using a novel approach, we found the temperature response of soil respiration in tussock grasslands primarily relates to root respiration, while soil warming has little effect on turnover of soil carbon.
This will improve our ability to predict the impact of soil warming on ecosystem carbon dynamics. This finding will not only contribute to more accurate global models of climate change, it will also improve New Zealand’s understanding of the likely impacts of a changing climate on our important soil resources.
This research is part of the Measuring Greenhouse Gases and Carbon Storage Portfolios, and was supported by Core funding.