We need to talk about nitrogen

The Soil Association has called for action to tackle the “overlooked” greenhouse gas that also causes harm to human health. Foodservice operators have a role to play, as Nick Hughes reports.

Isn’t nitrogen essential to life on earth? It certainly is. Nitrogen is a constituent of all living matter and is fundamental to food production since crops require nitrogen to grow.

So what’s the problem? Too much nitrogen becomes a damaging pollutant threatening climate, nature and human health. In a new report, the Soil Association says the growth in use of synthetic fertilisers, in particular, is contributing to climate change both through the greenhouse gas emissions produced during their manufacture and in the form of nitrous oxide emissions from the use of fertilisers in agriculture. The report cites research estimating that food and farming contributes more than half of all human-induced nitrous oxide emissions. It says emissions need to fall to near zero to achieve the widely shared ambition of net zero greenhouse gas emissions.

But is there any way to reduce emissions if we need nitrogen to produce food? Nitrogen is supplied naturally in animal manures which plants such as peas and beans then fix in the soil creating a virtuous nutrient loop. This is still a feature of agro-ecological and organic farming systems where grazing animals are rotated with nitrogen fixing crops to build soil fertility. But then synthetic fertilisers were invented.

So synthetic nitrogen bad, naturally fixed nitrogen good? Not exactly. The Soil Association notes that “nitrogen, and other nutrients like phosphorous, can leach from manures and ploughed grass leys, causing pollution of waterways and the atmosphere”. In its Achieving Net Zero report, the NFU said it is “an unavoidable consequence of soil processes that a small amount of nitrogen in an agricultural system will be emitted as nitrous oxide”. In summary, Soil Association chief executive Helen Browning, herself an organic farmer, says all farmers, including organic, need to manage nitrogen better.

What impacts are there besides greenhouse gas emissions? The Soil Association says reliance on synthetic fertilisers often leads to a reduced focus on healthy soil ecosystems that nourish crops. It cites Defra analysis showing that most arable soils in the UK have lost 40-60% of organic matter, washing away fertility and crucial soil carbon stocks. Excess nitrogen from intensive agriculture also risks creating dead zones in rivers and seas where it leaves aquatic ecosystems devoid of oxygen and life.

And what about the impacts on our health? An excess of nitrogen in the atmosphere from various sources – principally transport but also agricultural emissions – has been shown to have adverse impacts on human health including on lung function and growth as well as the respiratory system; it can also impact on asthma prevalence and incidence, cancer, heart disease and adverse birth outcomes. The Soil Association quotes data that estimates air pollution cuts short 40,000 lives across the UK annually, with an annual cost of up to £20bn.

Which foods are most nitrogen hungry? Modern varieties of wheat grown under intensive conditions provide extremely high yields but this productivity comes at a cost. Globally, wheat crops use almost half the total nitrogen fertiliser applied, while a recent life cycle analysis of a typical UK wheat-to-bread supply chain found that synthetic fertilisers account for more than 43% of the total global warming potential of a loaf of bread.

So we need to eat less bread? If only it were that simple. Cereal crops are often destined for animal feed, which is especially critical to intensive livestock systems; in Europe animal feed accounts for 80% of all nitrogen inputs, largely in the form of synthetic fertiliser. The Soil Association says this creates an additional issue in that the large volumes of manure generated can become a problematic waste product when not reapplied to the land in a rotational farming system. Manure releases nitrous oxides as well as methane, which can lead to greenhouse gas emissions during storage and processing.

So what are the solutions? The Soil Association says more efficient use of animal manures and greater use of nitrogen fixing crops in rotations will be crucial to replace synthetic nitrogen as part of the process of rebuilding soil fertility. In this regard, it says grass-fed ruminant livestock will play a crucial role. Technical fixes, such as adoption of precision farming techniques, can also mitigate the problem. In its net zero report the NFU points to the potential for the use of controlled release fertilisers and inhibitors to increase efficient use of nitrogen and reduce emissions. A report by the House of Commons environmental audit committee, in 2018, suggested the government also explore other incentives for reducing artificial fertiliser use, such as nitrogen and phosphorous budgets, and the concept of a nitrogen price. The government, meanwhile, is looking at setting stricter targets for levels of the most damaging air pollutants including nitrogen oxides as part of its new Environment Bill.

And how can foodservice operators play their part? Serving “less but better” meat and dairy is one way to affect rapid change, according to the Soil Association. It points to evidence showing that just applying nationally recommended healthy diets, such as the UK’s NHS Eatwell Diet, across populations would enable farming to reduce nitrogen (and phosphorous) application by 10-15%. Businesses can also look to source meat and dairy from extensive, outdoor and pasture-based livestock systems.

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