The agriculture sector is highly exposed to climate change, as farming activities directly depend on climatic conditions. That said, agricultural practices are also an important contributor, responsible for about 14% of the global greenhouse gas (GHG) emissions. It is recognised that with the right management practices agriculture has an important role to play in avoiding the worst impacts of climate change - through adaptation, emissions reduction and sequestration.
Other sectors (such as the energy sector) are actively and demonstrably reducing the GHG intensity of their production, thus increasing the pressure on agriculture to do the same. In this article, Sarah Wynn, who leads the Sustainable Food and Farming team of ADAS, sets out how food businesses can help farmers and their supply chains identify ways to reduce emissions and increase carbon storage on their farms. This article looks at a range of different approaches that can be taken to ensure that agriculture becomes a valuable part of the solution to combat climate change. Through demonstrating uptake of some of these approaches in their supply chains, companies can start to demonstrate how they are tackling scope 3 (supply chain) emissions. Read on to find out more.
The first step in reducing the GHG impact of agriculture is to reduce the GHG intensity of production. In cropping systems this can be done through a range of mitigation steps including:
- Optimising nitrogen fertiliser use
- Selecting low GHG intensity nitrogen fertilisers such as those produced using modern abatement technologies
- Reducing cultivation depth and frequency to reduce fuel use
- Switching to renewable energy sources for storage and irrigation energy
- Utilising new varieties that have lower input requirements to achieve the same yield
Other ways of reducing emissions, or capturing them to utilise for other purposes are captured below.
Additional ways to reduce or capture GHG emissions
Making use of manures | It is possible to capture the methane emissions from stored manures and use the gas for fuelling cooking facilities or even producing electricity. This can be done on small holder farms to provide local energy sources, or on a larger scale through anaerobic digesters to feed into existing power networks.
Organic manures can be used to replace some of the artificial nitrogen requirement of the crops, reducing embedded emissions from nitrogen fertiliser production. The incorporation of manures into the soil has the added benefit of increasing the soil organic matter content, increasing carbon storage.
Paddy rice | Rice production using paddy systems produces high emissions as a result of the methane produced under anaerobic (flood) conditions. By changing the duration of flood periods and periodically draining the land during the cropping season, methane emissions can be reduced with minimal increases in nitrous oxide emissions.
Burning | There are a number of crops, such as sugar cane, where burning of the crop residues is typical practice resulting in the emission of methane and to a lesser extent nitrous oxide. Therefore, finding crop management approaches, such as utilising harvesting machinery that can manage the whole cane plant, will minimise the need for crop burning and therefore reduce GHG emissions from production.
Soil health – source or sink?
The soil can act as either a carbon source (releasing carbon) or a carbon sink (storing carbon). FAO estimates that soils can sequester around 20 Gigatonne (Gt) of Carbon in 20 years, equivalent to 10% of the anthropogenic (manmade) carbon emissions. Therefore, it is important to promote practices that will enhance soil sequestration and minimise carbon losses from the soil.
Soil carbon | Using minimum tillage practices and applying organic manures, composts and crop residues, can increase the organic matter content of soils, with increases gradually accumulating over a period of years. There is a limit to how much carbon can be sequestered in soil, and the rate of sequestration will reduce and then finally reach equilibrium once soils reach saturation. The sequestered carbon in soils is also fragile and any change in management, e.g. a move away from minimum tillage practices, can result in sequestered carbon being rapidly released.
Peat soils | Peatlands are estimated to cover 3% of the Earth’s surface. The majority of peatlands are in the temperate Northern hemisphere (North America, Russian and Northern Europe), although 10-12% of the total peatland area occurs in the Tropics. Peatlands are a globally significant store of soil carbon. However, where peatlands are disturbed through deforestation, defrosting of permafrost, drought or drainage and cultivation they can become significant sources of GHG emission. The International Peatland Society estimate that degradation of tropical peatlands results in the release of approximately 2,000 Mt CO2e per year, making degraded peatlands an important source of global GHG emissions. Protecting peatland soils through maintaining appropriate vegetative cover, eliminating deforestation and ensuring that the water table is maintained is critical in maintaining these carbon sinks.
Vegetation – what about trees
Trees and other vegetation also having the potential to store carbon. Actions taken on farm to increase and preserve trees and other woody biomass will all contribute towards increased carbon storage.
Making best use of trees on farm
Agroforestry | The mixing of tree and crop species together can lead to increased carbon sequestration on farm as compared to systems that are using just crop species. Careful selection of tree species to include those that are also able to provide an economic return such as fruit and nuts can also make these systems highly beneficial to the farm, especially in small holder situations. There are a number of offsetting projects in developing countries where the purchase of carbon credits is able to support local farmers in accessing fruit and nut tree seedlings to plant on their farms. These trees provide shade and shelter, store carbon and also provide the farmers with a source of income.
Afforestation | Where deforestation is a potentially significant cause of GHG emissions, afforestation has the potential to capture and store carbon by increasing the biomass present on farm. Planting areas of woodland or forest can lead to accumulations of carbon in both the soil and more importantly in above ground biomass. The rate of accumulation depends on the growth rate of the tree, with faster growing species in favourable conditions capturing more carbon more quickly than slower growing species. The rate of accumulation will also tail off as plantations reach maturity. If forests are then harvested the stored carbon is only maintained if the wood is converted into long life wood products. If the wood is burnt or allowed to decompose the carbon will be re-released.
Agriculture is a source of significant GHG emissions at the global level. However, taking actions to reduce GHG emissions from common production practices, increase carbon storage in soils and capture carbon in trees and other vegetation has the potential to reduce and mitigate some of the GHG emissions arising from Agriculture. ADAS is able to help food companies develop strategies for monitoring uptake of these practices and develop metrics to quantify the impact of uptake on GHG emissions and carbon storage as part of monitoring their scope three emissions.
To find out more about how ADAS can help reduce GHG emissions and identify opportunities for increasing carbon storage in agricultural supply chains contact Sarah.Wynn@adas.co.uk.
About the author
Sarah Wynn is the managing director of the Sustainable Food and Farming business at ADAS. Sarah has 11 years’ experience working in the agri-food sector, with public sector organisations such as Defra, as well as corporate food and drink companies. Her work is primarily working with agricultural supply chains on projects related to sustainability and climate change.