Scientists have demonstrated how improvements in nitrogen fertiliser manufacture and their application could help reduce China’s agricultural greenhouse gas emissions by around 60%, by 2030, compared to the current business as usual approach. This emissions reduction represents a 2 to 6% reduction in China’s overall greenhouse gas emissions and therefore could be significant in the global battle on climate change.

In a paper published in the Proceedings of the National Academy of Sciences of the USA, the team from Rothamsted Research and China Agricultural University, working alongside other scientific colleagues in the UK and China, have quantified the total GHG emissions associated with nitrogen (N) fertiliser manufacture and use in China. They then examined several scenarios for reducing over-use and mis-use of N fertiliser, and for changing manufacturing processes, and calculated the decreases in greenhouse (GHG) emissions that could be achieved.

In this study, funded by the UK Foreign and Commonwealth Office and linked closely with projects funded by the Chinese Ministry of Agriculture, the UK-China team concluded that a combination of technical innovations in manufacturing and changes in agricultural management could result in annual GHG emissions being reduced to of 204 teragrams of carbon dioxide equivalents (Tg CO₂-eq) instead of the projected 542 Tg CO₂-eq by 2030 *

The UK leader of the project, Professor David Powlson said “China is the world’s biggest manufacturer and user of N fertiliser accounting for around 30% of global manufacture. A large use of N fertilizer is necessary for the nation to feed its 1.3 bn inhabitants. However, there is scope for using N far more efficiently: there is now clear evidence of widespread over-use and inefficient use of N fertiliser in China. For example there is evidence of 30 - 60% over-use in some regions

Synthetic nitrogen (N) fertiliser is an important agricultural product required to help promote plant growth and increase food production and has played a key role in enhancing food production. However, decades of N fertiliser overuse in several parts of the world have contributed to soil, water, and air pollution. N fertiliser has a large environmental footprint due to the emissions of GHGs during both manufacture and use, mainly as CO₂ evolved during manufacture and nitrous oxide (N₂O) evolved when the fertiliser is applied to soil. N₂O is a particularly potent GHG with a global warming potential almost 300 times that of CO₂.

To evaluate the impact of China’s use of N fertiliser, the team quantified the carbon footprint of China’s N fertiliser production and consumption chain using life-cycle analysis. They found for every tonne (t) of N fertiliser manufactured and used, 12.9 t CO₂-eq is emitted, compared to 9.7 t CO₂-eq in Europe. They then identified potential emission reductions by comparing prevailing technologies and management practices in China with other options worldwide. Mitigation opportunities included improving methane recovery during coal mining (coal being the main fuel used for fertilizer manufacture in China), enhancing energy efficiency in fertiliser manufacture, and minimizing N over-use on farms. The scientists found that use of these advanced technologies could cut N-fertiliser related emissions by 20-62%, amounting to 102-338 Tg CO₂-eq annually. Such reduction would decrease China’s total GHG emissions by 2-6%, which is significant on a global scale

The authors identify that achieving such decreases in N fertiliser use will be very challenging and require changes in national policies in China and they go on to make some recommendations of how that could be achieved. Professor Powlson of Rothamsted Research, who receives strategic funding from the BBSRC, noted that “to make these changes practicable for farmers various changes in policy and the current subsidy structure are essential: it is not simply a matter of better training of farmers.” The project came under the China-UK Sustainable Agriculture Innovation Network, SAIN (www.sainonline.org) that specifically supports research that has relevance to agricultural and environmental policies.