N2O - Is this the greenhouse gas vets can ignore?

If you are reading this there is a reasonable chance you are a veterinarian who is interested in sustainable agriculture and climate change. You probably have read around the subject a little; you may have studied some aspects in considerable detail and have decided to focus part of your clinical activity on assisting clients reduce their methane outputs. Because as far as the general public are concerned agriculture is all about methane, right?

This article, despite that rather tongue in cheek introduction, will provide a broad summary of greenhouse gas (GHG) emissions before taking a more detailed look at the forgotten greenhouse gas, nitrous oxide (N₂O) and the potential influence veterinarians can have on its emission.

Ignoring water vapour, which is an ever-present, rapidly changing, very potent greenhouse gas, the major greenhouse gases are: 

• carbon dioxide 

• methane 

• nitrous oxide 

• several fluorinated gases¹

In comparing their global warming potential, a scale based on the 100 year warming potential of carbon dioxide equivalents has been generally adopted, the so-called GWP CO₂e. Using this, each gas can be compared to the equivalent warming effect of carbon dioxide over one hundred years. This method has been criticised on numerous occasions, including within our own articles² but it remains the global standard. 

For example, using this benchmark, a fluorinated gas such as sulphur hexafluoride, widely used as an electrical insulator, emerges as the most potent offender, with a GWP of around 23,500 times the 100 year CO₂ figure. But it is generally only present in very low concentrations in the atmosphere and its overall impact is minimal. 

In comparison, methane has a calculated GWP of around 28 and, while it is short lived in the atmosphere, breaking down to carbon dioxide after 7- 8 years, it is common and firmly linked in the mind of many with agricultural sources. The debate around methane, produced naturally as part of the biogenic carbon cycle, and how best to measure it continues; the impact of CO₂ released by the burning of fossil fuels is now beyond debate. 

But what of nitrous oxide?

It is a very potent greenhouse gas with a GWP of 273 x CO₂e and a lifetime in the atmosphere of around 121 years. It can be argued that this makes it a more important greenhouse gas than methane and, unlike methane, its major sources are predominantly agricultural. There are a number of undeniably agricultural sources linked to the emission of N₂O including manufactured fertilisers, livestock waste, the decomposition of crop residues, and soil, especially compacted or wet soils. The leaching of nitrates into waterways, frequently linked to algal blooms, is a news topic that occasionally hits the headlines and farmer awareness is growing; but the fact that leached nitrates also produce N₂O is not widely known. 

Veterinarians are increasingly involved in discussions with farm clients that extend beyond their immediate areas of expertise in animal health and welfare. It is thus important that they understand the complexity of GHG emissions when discussing such matters. And nitrous oxide emission is a cornerstone of the GHG chemistry of any farm. 

Research into changes in types of fertiliser utilised can point towards ways in which N₂O can be reduced, see for example, the deployment of nitrification inhibitors with fertilisers³. But simple changes in animal husbandry and health practices can also aid the reduction of emissions of this potent GHG.

Consider animal stocking rates for example. This simple statistic links closely to the incidence of many diseases or welfare issues, whether stock are intensively housed or extensively farmed. In the former situation, where is the slurry or manure being stored and how is it being used? In the latter, are pastures being compacted by over-grazing or is it being poorly managed so that frequent tillage is required? A more holistic approach to farm management sees veterinary advice on animal health flowing into issues such as these and thus linking to reduced N₂O emissions.

Awareness of N₂O and its impact on a farm’s emission picture, is a critical part of the armoury of any veterinarian working in this area. By highlighting the fact that as a result of your revised advice on animal health, the farmer can carry fewer replacement young stock in future, and so can apply less nitrogenous fertiliser (or maybe apply it more precisely), you may just be providing the final piece of N₂O reducing evidence that your client needs, and so convince them to introduce your new animal health program!

In conclusion, farm emissions analysis involves numerous complex scenarios and it is currently difficult to make precise predictions, particularly where soil chemistry is involved. At VetSalus we are focused on assisting vets into this highly influential consultant role, where their undoubted knowledge of the complex interactions on farm, involving both animals and environment, places them firmly in the centre of many critical farm decisions.

How much longer can we allow N₂O to remain the invisible gas, the GHG that is too easily ignored?