A joint project between scientists in the UK and China has shown how improved methods of manufacturing nitrogen fertiliser and better use of it by farmers could reduce greenhouse gas emissions by hundreds of millions of tonnes a year.
The study’s published results show that fertiliser emissions could be reduced by up to 60% by 2030, representing 2-6% of China’s total annual greenhouse gas emissions. Achieving this will require changes to current policy regarding subsidies and incentives in the fertiliser industry. But these are globally significant implications - one third of all the world’s nitrogen fertiliser is manufactured and used in China, and nitrogen fertiliser has a large greenhouse gas footprint.
It may seem surprising that agriculture and fertiliser are significant contributors of greenhouse gases – more usually associated with heavy industry or transport. In fact the last report of the Intergovernmental Panel on Climate Change (IPCC) concluded that agriculture contributed about 14% of global carbon dioxide, nitrous oxide and methane emissions – almost the same as from transport. Of that, about 70% of agriculture’s contribution to greenhouse gas emissions is associated with nitrogen fertiliser.
Where does this come from? The energy demands from factories manufacturing fertiliser creates carbon dioxide. This is worse in China than most countries as coal is the main source of energy rather than less polluting natural gas. Fertiliser, once applied to the soil, generates nitrous oxide - an extremely powerful greenhouse gas, with a global warming effect almost 300 times stronger than carbon dioxide.
China needs to use large amounts of fertiliser if it is to feed its 1.3 billion inhabitants. But there is scope for using it far more efficiently, and there is clear evidence from Chinese researchers of widespread over-use - as much as 30-60% in some regions.
Over-use of fertiliser also contributes to other environmental problems - especially water pollution. Growth of algae in China’s numerous lakes is promoted by nitrate and phosphate running off agricultural land. Algae interfere with fisheries, nitrate concentrations in drinking water frequently exceed regulatory limits, and ammonia from nitrogen fertiliser and from manure contributes to poor air quality.
The scale of the problem
Using life-cycle analysis, the team quantified the carbon footprint of China’s fertiliser production and consumption chain and found that each tonne of fertiliser created 12.9 tonnes of carbon dioxide equivalents (CO2-eq), compared to 9.7 tonnes CO2-eq in Europe. We identified potential emission reductions that included better methane recovery during coal mining, energy efficiency in fertiliser manufacture, and minimising fertiliser over-use.
Taking advantage of manufacturing innovations and better agricultural management could cut fertiliser-related emissions by between 20 and 62%, amounting to 102-357 teragrams CO2-eq annually (one teragram is equal to 1012 grams or one million metric tonnes). Such a reduction would decrease China’s total annual greenhouse gas emissions by 2-6%, which is significant on a global scale.
China has moved from a position of severe food shortages several decades ago to being one of the world’s most food-secure countries. Affordable and available fertiliser has contributed to this, but there is now overwhelming evidence that it is being used in excessive quantities and applied in inappropriate ways. Farmers are generally not well educated so they assume that if some nitrogen is good for crop yields, more will inevitably be better. It is a difficult matter for policy makers - because food security is such a key issue, they are reluctant to acknowledge that there is an over-use problem.
Changing policy and practice
The project team proposes removing subsidies on nitrogen fertiliser, increasing its price and forcing people to use it more rationally. But this has political risks if farmers feel they are being penalised. However, we propose that finance currently spent on subsidies could be reallocated to promote a specialist farming contractor sector. This would be made up of contractors who could apply the fertiliser at the right time and in the right quantity. This would be applied with the appropriate machinery to maximise the benefits and minimise losses and emissions, but which small farmers cannot afford to buy themselves. This would bring better farm management and environmental benefits, and cost neither the government nor farmer any more. This trend already occurs in other aspects of farming, for example contractors paid to harvest crops using small combine harvesters, to avoid the back-breaking labour of hand-harvesting. In fact contractors are often farmers who move into this activity, representing a degree of specialisation.
The Chinese government’s highly influential National Development and Reform Commission, has established a set of Low Carbon Pilot Zones where policies aimed at decreasing greenhouse gas emissions are to be tested. We hope our proposals will be taken up and piloted here, to realise the considerable potential benefits of more rational fertiliser use - for China and the rest of the world.