A five-year UK research project has concluded that greenhouse gas (GHG) emissions due to nitrogen fertilisers used on UK arable land are less than half the levels previously estimated. Therefore, most UK arable food products are likely to have smaller GHG intensities than currently estimated, while biofuels made from crops fertilised with nitrogen products are more effective in reducing GHG emissions than has been assumed.
Nitrous oxide (N2O) is an important GHG thought to contribute 41% of agriculture’s GHG emissions. The Minimising Nitrous Oxide (MIN-NO) project was sponsored through Defra’s Sustainable Arable LINK programme with £300,000 funding from AHDB Cereals & Oilseeds. It ran from 2009 to 2014. Led by Roger Sylvester-Bradley, head of crop performance at ADAS UK, the research involved a consortium of 23 government, academic, farming and commercial partners with interests in the future sustainability of the food, feed and fuel supply chain. It used multi-site industry data, field experiments and modelling to improve estimates of N2O emissions associated with the major UK arable crops and their products.
The work used 24 field experiments across widely contrasting rainfall, soil and crop conditions. Of the 24 sites, 21 showed that direct N2O emissions due to fertiliser nitrogen (N) were less than the 1% default emission factor (EF) assumed by the influential Intergovernmental Panel on Climate Change. A simple model summarising these emissions predicts a 30-year average EF for arable land across the UK of only 0.46% of N applied.
The researchers than went on to devise a set of ‘smart’ EFs for consideration by UK stakeholders, based on the MIN-NO model, other MIN-NO results and associated evidence. The smart EF for fertiliser N predicted a decrease in emissions of almost 10% of the previously estimated total N2O-N emission from UK agriculture (which excludes fertiliser manufacture).
The greenhouse gas (GHG) intensity estimated with the MIN-NO smart EFs (which include reduced GHG from fertiliser manufacturing plants modified to abate nitrous oxide), when expressed as emissions per tonne of UK feed wheat, was 20% less than the ‘benchmark’ GHG intensity using a current default methodology. Similar smart EFs gave a reduced GHG intensity for harvested rapeseed, but similar intensities for sugar beet and an increased intensity for vining peas.
The project also confirmed that sourcing of nitrogen fertilisers from production facilities which are abated makes a substantial reduction in the Greenhouse Gas (GHG) footprint of the final marketed product whether it be chicken, cooking oil, whisky or a biofuel product.
Therefore, most UK arable food products are likely to have smaller GHG intensities than are currently estimated at present, states the project report while biofuels made from N-fertilised crops could be considered more effective in reducing GHG emissions. Choosing fertilisers with the lowest carbon footprint leads to a reduction in the GHG footprint. For example, bread can be reduced by 7%, bioethanol from wheat by 15% and biodiesel from oilseed rape by 16%.
On the downside, the research found that there is less prospect mitigating the N2O emissions associated with UK arable cropping than was previously thought. “Farmers already using abated N fertilisers and following good practice lack any easy means of further mitigation.” In other words, further reductions will require investment, whether in employing more sophisticated crop nutrient supply systems and /or by growing more N-efficient crop species and varieties. This could result in a further 30% reduction for the harvested produce of most crops, and savings of 5% to 25% for their food or fuel products. Further research is needed for other options such as cultivation strategies to improve soil conditions.
“This research is the most ambitious to date in providing a comprehensive national assessment of nitrous oxide emissions in actual farming conditions, and has significantly improved scientific understanding in this important area,” says Dr Sylvester-Bradley.
For the AIC, chief executive David Caffall notes: “It is pleasing to see the massive investment by the supply industry is also having potential added value in the market place.”
Richard Laverick, the new chief technical officer at the restructured AHDB, adds:”The project has provided our industry with a vital and far more accurate understanding of the behaviour of nitrous oxide emissions in arable agriculture. It will help inform all involved in producing for the food, feed and biofuel supply chains. The findings are significant and will make a major difference to the UK’s ability to meet sustainability criteria for a range of supply chains.”