We asked Professor Peter Grace, of Queensland University of Technology’s School of Biology and Environmental Science, to talk to us about carbon-neutral agriculture, and specifically, to comment on TERN’s role in achieving it.
Peter has been involved with TERN since its commencement and among his many current projects, he works with industry, looking at the carbon balance of grasslands. Peter has also been active over an extended time in both the developed and developing world promoting the use of simple soil assays and educating land holders in soil management for maximising long-term productivity and profitability.
In the National Inventory Report 2021, the Australian Government Submission to the United Nations Framework Convention on Climate Change, released April 2023, Australia’s net greenhouse gas emissions from all sectors were 464.8 million tonnes (Mt) of carbon dioxide equivalent (CO2-e) for 2020-21. Second only to the Energy sector, in 2020-21, Agriculture sector emissions (excluding the category of Land use, land use change and forestry) comprised 14.8% (see Fig. 1).
While Fig. 1 reports that the Agriculture sector is our second highest greenhouse gas emitter when measured on a carbon dioxide equivalent basis, the specific greenhouse gases emitted in the sector include those that are more potent than carbon dioxide, making agriculture by far the largest emitter. Methane, of which cattle gut fermentation is a major source, has 25-30 times the greenhouse effect of carbon dioxide. Nitrous oxide has 300 times the greenhouse potential of carbon dioxide, and nitrogen fertilisers are the largest source of that. The livestock sector has a large greenhouse footprint, producing 59 percent of all methane and 86 percent of nitrous oxide in Australia. Nevertheless, sustainable farming practices could play a major role in the mitigation of global warming and promote productivity
Agricultural soils are a major source of carbon dioxide, which is not a problem providing output balances input i.e., from plant uptake or addition of carbon. The problem is when output exceeds uptake, as has been the case historically in Australia and most of the world. Soils contain the Earth’s largest pool of organic carbon: 20 tonnes in the top 10 cm of a typical Australian professional sports field, for example. Yet decades or centuries of conventional farming in Australia have depleted and continue to deplete this resource. Microbes decompose the soil carbon, releasing it to the atmosphere. The lost carbon can be replenished via careful management, and doing so offers numerous benefits.
Increasing Soil Organic Carbon: recarbonising soils
There is a global trend towards recarbonising agricultural soils, which has become a major international movement since 2015. Cropping systems have made some progress in this direction, but grazing lands generally have not yet and as such vast areas exist, a small increase in soil carbon adds up to be a significant number when it comes to recarbonising our landscapes.
Recarbonising soil results from stimulating and increasing biomass above and below ground. Practices collectively known as conservation agriculture – e.g., switching to permanent pasture, rotational grazing, and no-till (i.e., reduced or no cultivation) farming – strongly foster this increase. Carbon added to the soil comes from the atmosphere and occasionally from external sources such as animal manures, mitigating global warming. Increasing soil carbon also improves soil health and productivity. Healthy soils are more resilient and more productive, and thus more profitable for farmers. High soil carbon indicates an abundance of all other key nutrients.
However, navigating the decisions involved in conservation agriculture is not simple. For example, adding any nitrogen fertiliser could switch a farm from being a carbon sink to a nitrous oxide source. Also, years of conventional farming impacts soil structure and increases the incidence of waterlogging which can dramatically increase both methane and nitrous oxide emissions as well as reduce productivity. Careful management is needed, and that depends on monitoring, which is one of TERN’s roles.
TERN’s monitoring roles
TERN’s development of the national soil and landscape grid, which is soil information layers at 90 metre resolution, has been critical to identifying areas where the soils are most suitable for carbon storage. Not all soils are suitable. Clay soils, common in Queensland and northern New South Wales, have the greatest potential for storing carbon.
One thing farmers need to know is whether their soils are actively storing carbon. The TERN/Ozflux network of eddy co-variance flux towers can help farmers determine this.
Instruments on the towers measure the real-time exchange of gases (especially CO2), water and energy between plants, soil and air. Three of TERN’s towers permanently monitor this exchange on farmland, while a consortium of funding agencies led by the Meat and Livestock Australia and private industry has added a supplementary network of towers, including portable versions, targeted specifically at increasing carbon storage on grazing properties. The TERN-OzFlux network, already of world-class capability, could potentially be expanded, and Australia is fortunate to have additional public/private investment considering this. Tower measurements are much more efficient, more accurate, and more reliable than traditional soil sampling, also fairly low cost by comparison. They are very low maintenance too. The TERN flux towers integrate data from a wide area (10-50 hectares), negating the inherent problem of local soil variability. Flux towers also measure albedo (reflectance), which indicates pasture palatability, and evapotranspiration, which indicates the efficiency of water usage. The data these instruments gather help refine soil carbon-cycle models as well as provide basic information to landholders to inform management decisions both now and into the future.
Another of the key advantages of the flux towers is immediacy. Farmers do not have to wait to know whether their management is having the desired effect. Farmers can input certain parameters about their farm into special ‘online calculators’ (for example, see www.n2o.net.au/greenhouse/). These calculators process tower data and the farmers’ information according to soil carbon-cycle models, enabling farmers to dynamically assess soil carbon storage. Thus, the TERN infrastructure allows farmers to very accurately determine whether their management practices are actually leading to the sequestering of carbon. If they are, farmers may qualify to receive credits under the Australian government’s Emissions Reduction Fund. Conventional measurement techniques take much longer, are far more expensive and coarse and are unlikely to show improvement as accurately as the flux towers, making it more difficult for farmers to qualify for the credits.
TERN’s role of long-term monitoring and management of the environment is absolutely critical for carbon neutral agriculture at scale. A farm may sequester carbon during a favourable period only to lose most of that during the next drought, yielding a net loss over an extended time. Permanence of carbon storage is a critical variable in the Government’s program. Also, practices that release methane or nitrous oxide are considered carbon debits in this scheme. For example, clay soils are prone to waterlogging, which can release nitrous oxide and the over-use of nitrogen fertilisers.
TERN provides the data essential both for refining soil carbon models and for developing management practices that improve soil and produce a productive, resilient environment. Ultimately, TERN helps farmers navigate and evaluate complex management decisions, including those potentially leading to recarbonisation and carbon-neutral agriculture.
