Synthetic Nitrogen - Can't live without it, Can't live with it

Without doubt the elephant in the room when discussing the environmental costs of food production is nitrogen. The so called Green Revolution was triggered by the ability to convert atmospheric nitrogen into a usable form for agricultural production. The Harber-Bosch process, by which synthetic nitrogen is produced, made nitrogen cheap and readily available. Today we put 80 million tons of synthetic nitrogen on agricultural fields every year at a cost of more than $100 billion.

But there is nothing green about it. There is a massive environmental cost associated with this nitrogen production and use and like many environmental issues much of that costs cost is externalised, kicked down the road to be dealt with another day. Synthetic nitrogen has enabled us to grow food production to keep up with the world's burgeoning population but it is simultaneously ensuring that we will not be able to carry on producing food at the rate we need to.

The production of synthetic nitrogen is very energy intensive using up a little over a 1% of world's annual energy production. Mostly this is from natural gas and aside from the high energy use it is also associated with significant methane emissions. This energy intensive product is also incredibly wasteful. Once the nitrogen hits the field the majority leaks away with only between 10 and 40% making it to the plants it was intended for. So where does the remaining 90-60% go? It doesn't remain in the soil for next year's crop but rather leaks into our water and our atmosphere.

Much of this nitrogen makes its way into our ground water, streams, rivers, lakes and seas. The excess nutrients cause eutrophication, massive algal growth, which in turn causes toxic conditions where nothing else can grow. This results in dead zones with the most infamous example being the large dead zone at the mouth of the Mississippi River. Dead zones have been reported from more than 500 coastal and inland water systems across the world, affecting a total area the size of Germany. In the EU 40% of surface waterbodies and more than 50% of groundwater sources are affected by nitrogen pollution. In all cases the main source is agricultural fertilisation.

Nitrogen also volatilises to form nitrous oxide (N2O) in the atmosphere, nitrous oxide is commonly known as laughing gas but when it comes to greenhouse gasses it is no laughing matter. It is 298 times more potent than carbon dioxide and agriculture - mostly fertiliser and poorly managed manure - accounts for 60% of anthropogenic nitrous oxide emissions.

In terms of food production synthetic nitrogen has a major negative impact on soils, organic matter, carbon stocks, acidity and soil microbiology are all adversely effected. These impacts decrease the capacity of the soil to function effectively and over time more and more nitrogen is needed to make up for the deteriorating soil. Between 1961 and 2010 synthetic nitrogen use in agriculture increased 6 times.

The wheat plants in this picture were planted with nitrogen fertiliser applied below the seed and then an organic fertiliser was added on the surface. There is a clear line at the level of the seed, you can see that below where the synthetic nitrogen was applied no association between the soil and the root has taken place. Above the seed you can see a healthy rhizosheath. Credit: Dr Christine Jones

The addition of synthetic fertilisers also limits the ability of plants to take up minerals and trace elements. Due to the "free" nitrogen, phosphorus and potassium from the fertiliser plant roots do not develop the appropriate relationships with soil microbiology. Without relationships with soil bacteria and fungi the plant is unable to access the other minerals and crucial trace elements from the soil. The result is well grown but nutrient deficient plants.

 
Excess nitrogen in plants also makes plants more susceptible to attacks from pests and diseases resulting in more pesticides having to be used.

Oat roots with nitrogen fertilizer (left) and without (right) showing how the nitrogen fertilizer stops the development of a healthy rhizosheath. Photo Credit Phill Lee

Finally when synthetic nitrogen breaks down it forms ammonium and nitrate. Nitrate (NO3) has the ability to form carcinogens. Aside from the nitrates that leak into our drinking water it also makes its way from the soil into our food. When synthetic nitrogen is applied in high levels to soils lacking in micro organisms and available carbon the nitrate can't be converted to amino acids. This results in plants taking in nitrates and accumulating them in the fruits, vegetables and grains we eat.

For all of the above reasons arguably the single biggest thing man could do to improve our rapidly deteriorating environmental situation is to switch off synthetic nitrogen production. This would force a regenerative revolution as farmers would quickly have to move to alternative sources of nitrogen and the only way to do that would be to farm regeneratively. Aside from the negatives of synthetic nitrogen slowly disappearing from the planet there would be all the other positives of regenerative agriculture like fixed carbon and water cycles, and the slowing of biodiversity loss.

There is an example where this has occurred but due to politics rather than environmental and health concerns. In Cuba after the collapse of the Soviet Union they lost access to subsidised Soviet fertiliser and overnight they had to change the way they farmed to stop the county starving.

One way we could cut back nitrogen use and bring about change would be to introduce a tax for synthetic nitrogen. The tax would be to cover the true cost of its use, just like companies paying a carbon tax. The tax could be a progressive tax that increases over time giving the agricultural industry time to adapt.

Of course the establishment will scream from the rooftops that this isn't possible and that the world will starve. But there are millions of farmers across the world producing food without synthetic nitrogen and it is well known that the problems of hunger across the planet are not caused by insufficient food production. In the US, which produces a third of the worlds maize, the vast majority of that maize crop goes to ethanol and livestock, not people. Global hunger is about access not production.

Secondly as the understanding of soil microbiology and how plants and soils interact improves the capacity to get soils to be highly productive without synthetic nitrogen grows. There are many bio-stimulants that are progressively being added to global food production and together with the diversity from cover crops and crop rotations these can all work to replace synthetic nitrogen in our food production.

Perhaps it's time to stop kicking the can down the road. It's certainly time to start discussing stopping.

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