Reduce nitrogen fertiliser and use urease inhibitors

Reducing the use of nitrogen-based fertiliser is a measurable way of reducing the amount of nitrogen entering the soil that's available to be transformed into nitrous oxide.

How it works

Nitrous oxide is produced by naturally occurring soil microbes. The microbes convert urea or animal urine into different forms of nitrogen, such as ammonium and nitrate, but also nitrous oxide.

Reducing nitrogen-based fertiliser use is a step that all farmers could consider. (Note that nitrogen-based fertilisers also release a small amount of carbon dioxide when applied to land, so reducing their use will reduce that gas as well as nitrous oxide).

Another action to consider is the use of fertiliser containing urease inhibitors. This reduces volatilisation losses of ammonia from urea use and maximises nitrogen available for plant uptake, meaning less nitrogen needs to be used (typically 10%), which in turns leads to less nitrous oxide being emitted. Urease inhibitor use is increasing in New Zealand - currently around 35% of urea sold has a urease inhibitor coating

Farmers and growers could also consider using precision agriculture technologies to ensure nitrogen-based fertiliser is applied only in the places and quantities needed. See the farmer case studies featuring Jay Clarke (horticulture) and Craige Mackenzie (arable) for more information on this approach. 

More information on fertiliser use in New Zealand can be found on the Statistics New Zealand website

How will this affect my GHG number?

Emissions from nitrogen fertiliser use make up about 3.7% of New Zealand's carbon dioxide equivalent agricultural emissions. Research for the Biological Emissions Reference Group found that if all nitrogen fertilisers in New Zealand were coated with a urease inhibitor, the national reduction in carbon dioxide equivalent emissions would be 0.2%. Therefore, reducing nitrogen fertiliser use won't have a big impact nationally. It can, however, substantially influence the emissions from cropping and horticultural enterprises.

Reducing nitrogen fertiliser use will also have co-benefits for reducing nitrogen leaching. High nitrogen fertiliser use on pastures can also mean a high concentration of nitrogen in the diet of grazing animals, resulting in increased nitrogen in urine, which influences nitrous oxide emissions and nitrogen leaching losses.

Many farmers and growers have already done all they can to reduce nitrogen fertiliser use, often with the help of nutrient budgeting tools like OVERSEER and/or implementing good management practices through Farm Environment Plans. If you haven't already, you should also find out what your on-farm greenhouse gas emissions are.

Risks

Plants need nitrogen to grow and sub-optimal nitrogen supply will affect plant productivity, resulting in reduced crop and pasture yields. On pastoral farms, if reduced pasture production means more off-farm feeds need to be purchased, profitability could go down while the net reduction in emissions may be negligible.

More information

For more on the sources and science of nitrous oxide, see: