Nitrogen fertiliser has helped provide abundant food – but at the same time has undermined the natural systems that sustain us, contributing to global warming and damaging human health. Excess nitrogen issue creates luminous green pastures, though they look healthy they are in fact wildlife deserts. Is there a way to feed ourselves adequately whilst reducing the amount of reactive nitrogen created in the process?
Soil Association has recently released a report title Fixing Nitrogen – The challenge for climate, nature and health. Here is an excerpt.
Beyond greenhouse gases there is the additional risk of nitrous oxide contributing to ozone depletion. The big ozone depleting gases hydrochlorofluorocarbons (HCFCs) have been successfully phased out globally through the UN Montreal Protocol, 1987. This is the big global climate success story, but nitrous oxide sits outside of this regulation and is on course to become the top ozone-damaging pollutant in the 21st Century.
Some potential answers to the main challenges of reducing dependence on synthetic nitrogen and suggest areas for further research and exploration.
What happens to yields when nitrogen is reduced?
Nitrogen is often used in excess, and inputs can be dramatically reduced without any significant yield reductions. In China, it has been estimated that a 30-50% reduction in fertiliser use can be achieved without any negative impact on yields.
The Defra Soil Nutrient balance shows that in the UK almost half (45%) the nitrogen applied to farmland is surplus. Much of this is lost to the environment. The UN Environment Programme’s Colombo Declaration has recently established the global ‘Halve Nitrogen Waste’ campaign, highlighting the fact that improving nitrogen use efficiency not only supports climate, nature and health goals, but also saves US$ 100 billion globally annually.
However, reducing these inputs is only the first step, after which farm systems would need to be reoriented to focus on recycling nutrients and on healthy soils.
Are there alternatives to synthetic nitrogen issue?
Farming has historically captured atmospheric nitrogen issue through ‘biological fixation’, using leguminous plants and utilising animal manures. Mixed farming systems today rely on legumes like clover and field beans to capture nitrogen as part of their rotation. However, the intensification of agriculture and rise of synthetic fertilisers over the past century is mirrored by the fall of biological crop fixation. European data estimates that natural nitrogen accounted for 80% of annual nitrogen input in 1900. In 2000 it was just 5%, and all the while total input has increased four-fold.
Because farm practices that work to capture nitrogen through leguminous crops limit the total load of nitrogen that can be applied to a field, nitrogen is viewed as a valuable resource, too good to waste. Without the short-cuts of synthetic nitrogen inputs, agroecological systems rely on the health, quality and structure of soils to support crops. It is these healthy soils that absorb run-off, filter nutrients and have a higher volume and diversity of soil microorganisms to break down nutrients more effectively.
Many of the practices inherent to agroecological farming, such as cover-cropping, are widely practiced as techniques to conserve nitrogen. It improves soil structure, protects soils from erosion and leguminous cover-crops like vetch can also fix inert nitrogen at the same time.
Effective utilisation of animal manures is also key to efficient nitrogen use and is facilitated in mixed farming systems. The intensification and specialisation of farming systems have separated livestock and crops, and the geographical clustering of these systems leaves multiple nutrient management challenges.
Areas of intensive livestock production depend on high fertiliser and feed inputs and create large volumes of manure and slurry, often impacting surrounding areas with nitrogen pollution. Meanwhile areas specialising in crop production have challenges accessing animal-based nutrient sources due to large distances, increasing the incentive to resort to synthetic fertiliser input.
Global nitrogen flows such as through the import of protein crops for animal feed (e.g. soy from South America to Europe) create similar problems of nutrient transfer at a macro level, enabling the intensive livestock units that generate local excess nitrogen.
Legislative approaches to encourage a shift away from synthetic nitrogen include the EU Fertilisers Directive, which will operate alongside the Circular Economy Directive and the recent Farm to Fork Strategy. These policies incentivise a shift to recycled nutrients and reduced reliance on imports and fossil fuels, while reducing the associated contaminants and heavy metals present in many synthetic fertilisers.
Can soil health be maintained with less nitrogen?
Yes; in fact too much nitrogen damages soil health. Inputs of synthetic nitrogen are not essential for soil fertility and in practice their use tends to undermine long term soil health. Functioning soil is an essential part of making nutrition available to plants.
Reliance on synthetic fertilisers often leads to a reduced focus on healthy soil ecosystems that nourish crops, with knock-on consequences for soil health, structure and resilience to erosion, as well as biodiversity and greenhouse gases.
This trend has had grave consequences for soil health: Defra analysis shows most arable soils in the UK have lost 40-60% of organic matter, washing away fertility and crucial soil carbon stocks.
Though synthetic fertilisers may give an immediate productivity bounce, new studies highlight the depth of negative effects they have on soils, altering their complex communities of microbes, slowing decomposition rates, reducing available nutrients and ultimately stunting plant growth.
Nitrogen is required to maintain soil fertility, but its balance with other elements is critical. Carbon and nitrogen are in a fine balance in soils; getting this balance right has significant implications for soil emissions, health and crop yields. Despite huge leaps forward in soil science in recent years, there is still a significant gap in understanding the dynamics of nitrogen in soils.
Do diets need to change in a world with less nitrogen issue?
Adequate food production within planetary boundaries is clearly an overriding priority. Yet, even with current excessive nitrogen use, millions of people are malnourished. The intention to increase food production for a growing global population needs to recognise planetary boundaries and the challenge of nutrient supply in nitrogen-scarce regions.
Many areas of the world (e.g. sub-Saharan Africa) have a serious nitrogen deficit with implications for farm productivity. Increasing the availability of reactive nitrogen in these regions is essential to address world hunger and maintain productive soils, and this can be achieved with minimal negative impacts on climate, nature and health.
Facing this global context of constrained nitrogen issue, fairer distribution is essential. In any future farming scenario – including a lower nitrogen one – significant diet change will be necessary. Modelling suggests that, in Europe, feeding a growing population a sufficient diet is possible without the need for synthetic nitrogen.
High meat consumption diets are by their nature nitrogen intensive; livestock are overall poor nitrogen converters. In these cases, eating ‘less but better meat’ and dairy is one clear way to affect rapid change. Even just applying nationally recommended healthy diets – e.g. the UK NHS Eatwell Diet65 – across populations would enable farming to reduce nitrogen (and phosphorous) application by 10-15%.
Diets currently reliant on meat and dairy from intensive livestock systems will need to shift to lower output extensive, outdoor and pasture-based livestock sources.
Models such as the ‘livestock on leftovers’ approach – that uses non-human edible crops and residues to supplement animal nutrition – are an integral element of a closed-loop food system. They should be deployed to supplement these extensive livestock systems.
All this implies drastically reducing the reliance on commodity crops for animal feed and repurposing arable animal feed crops for direct human consumption; significant reductions in pig and poultry production would follow.
The way through the nitrogen issue challenge
First, there must be recognition that nitrous oxide emissions have been seriously overlooked in global climate change mitigation models, whilst possibly excessive attention has gone to methane.
On the international level, greenhouse gas accounting needs to include the full climate impact of synthetic fertilisers, and the imported food and feed that rely on them in order to inform national policy making. This will undoubtedly necessitate a fundamental reduction in the amount of reactive nitrogen that is continually being added to the global environment.
Nitrogen must be a key focus at the global climate summit, COP26, where there is a clear opportunity for UK leadership.
At national level, because nitrogen impacts are so wide-ranging across climate, nature and health, policy and legislative responses have tended to be compartmentalised across air quality, environment, agriculture and climate objectives. Whilst this is inevitable, an overview is needed to realise synergies between approaches to the different impacts.
Building on experience of controlling emissions from the industrial sector, sustainable nutrient limits need to be set within catchments and permitting, and planning regulations and advice targeted accordingly.
At farm level, there is a need to incentivise, plan and regulate farm practices for nitrogen to reduce impacts in the most efficient way and secure win wins. Most of the farm practice solutions to reduce nitrogen pollution are good for farm business efficiency as well as for nature, health and climate.
Some of these actions are likely to be fairly generic across farms (for example good slurry storage) whilst others will be highly specific, such as maintenance and restoration of species rich grasslands by targeted reductions in inputs. Overall, empowering farmers to innovate solutions, reduce their reliance on high fertiliser application, and transition to alternative farm systems is an opportunity for, and responsibility of, government.
System-level change – a transition to agroecology?
If nitrogen is an issue that needs to be tackled across multiple policy areas, are there joined up approaches that can deliver? One possible approach is agroecology, which at its core is a farming system that works with natural processes to produce food, fuel and fibre, positioning a farm system within natural cycles, including the nitrogen cycle.
Agroecology is a systemic approach that can help tackle the nitrogen challenges we face. A recent model by the think-tank IDDRI has laid out the pathway for Europe to become agroecological by 2050.68 As a systemic approach to the challenges above, it shows how agroecological food and farm systems can facilitate:
- A sustainable healthy diet for all. When viewed from a food system sustainability context – e.g. changing diets and reducing waste69 – a healthy diet can be provided for a growing European population while remaining within planetary boundaries for key risk areas such as nitrogen surplus.
- A shift to circular approaches to nutrient flows, meaning nitrogen and other key nutrients like phosphorous are treated as a resource too good to waste. A recent meta-study from North America shows that on average an organic farm system uses recycled nitrogen for 50- 100% of total needs, while conventional systems are found to only recycle 10-30% of nitrogen and are dependent on synthetic fertiliser in most cases.
- Improved soil health for nature, climate and our long-term food security. Soil science has raced ahead in recent years, and good soil stewardship is today underpinned by the practices of agroecological farming such as cover-cropping, agroforestry and crop rotations. Farm productivity benefits too; farmers have known for generations that boosting soil health and biodiversity can increase crop yields.
Food and farming supplies in the UK have been shown to be vulnerable to external shocks. Our lack of emphasis on domestic food supply should be viewed as a food security concern. More so, the reliance on fossil fuel imports for synthetic fertiliser input leaves us not only undermining netzero climate commitments, but vulnerable to geopolitical and market shifts.
Agroecological approaches offer resilient alternatives to the status quo by closing these nutrient loops and reducing loss and input requirements. These options are essential in a resource constrained world.
We have recently seen that governments are prepared to intervene on food access, availability and distribution. This enthusiasm should be harnessed to transition to healthier diets that support more sustainable and resilient farming systems as part of getting to grips with the nitrogen challenge.
Source: https://www.soilassociation.org
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