As a quick reminder, ammonia is a gas made from nitrogen and hydrogen. Ammonia loss is almost totally associated with agriculture and farming accounts for 99% of all emissions. Because it is a pollutant, it is considered essentia,l but agriculture is beginning to grapple with this problem. As well as being a loss of nitrogen from the land, it is also a challenge too our heritage and sensitive ecosystems.

Being a gas, ammonia is easily taken up into the atmosphere. But it is also very soluble in water and dissolves in rain to be washed back down again to earth. This means that nitrogen (N) is leaving nitrogen risk-intensive agricultural systems, but potentially falling on low-end sensitive parts of the country. Most people can imagine the consequences of N being washed down and back onto a sensitive landscape like the boring in Co Clare. But there are many other equivalent sensitive areas we may be less conscious of.

As well as the impact of rain-washed N on ecosystems, it can also be a problem for surface water. Rain that contains additional N as dissolved ammonia can increase the N levels in highly-sensitive water bodies. Here, elevated levels of N can cause serious problems, both to the life therein and to the potential for eutrophication in that water body.

For these reasons, it is important for farming to address the problem of the ammonia loss. The major sources of ammonia loss are associated with livestock enterprises and the application of nitrogen fertiliser, especially urea. The categorisation of the losses is shown in the chart above, with almost 90% associated with livestock systems.

The N conundrum

Different forms of N fertiliser present different risks of ammonia loss. By far the lowest offender for ammonia loss is CAN, with an estimated 0.8% loss. Urea, on the other hand, is by far the worst offender, with 15.5% potential loss as ammonia. Protected urea is being designed to reduce this risk and Teagasc estimate that its ammonia loss is down to 3.3%.

So why are Teagasc recommending protected urea when CAN has even lower ammonia loss risk? The reason is that protected urea represents lower overall environmental risk when both ammonia and nitrous oxide are taken into account.

It is acknowledged in the Teagasc assessments that a switch to protected urea will slightly increase ammonia emissions relative to CAN, but the net benefit is far greater when the reduction of the more damaging nitrous oxide is assessed.

The major sources of ammonia loss are associated with livestock enterprises and the application of nitrogen fertiliser, especially urea

That said, it is important to realise that N forms are continuously changing in soil. This change, or transformation, is generally brought about by soil organisms, but the degree and direction of change is influenced by other management factors such as soil pH and the concentration of N in the soil.

Having soil pH up around the optimum of 6.2 to 6.5 for grassland helps in the utilisation of all nutrients. This, in turn, helps in the utilisation of N, as it allows more growth to take place. The more of the total N that is used by growing plants, the lower its concentration in the soil will be and, therefore, the lower the risk that some of that N will be turned into ammonia and lost.

We cannot escape the fact that high nitrogen levels in soil are, in themselves, a driver for ammonia production and loss

Ammonia can be lost following any form of N fertilisation, but it would be slower with CAN and faster following urea. However, even with protected urea, having high or concentrated N levels in the soil will most likely result in transformation into ammonium, then into ammonia, and volatilised, or lost as gas.

So, we cannot escape the fact that high nitrogen levels in soil are, in themselves, a driver for ammonia production and loss. The only way that this can be tackled is with a reduction in the overall soil N levels. Getting this optimum rate right is a challenge, but achieving an improvement in nitrogen use efficiency brings many rewards to both the farmer and the environment, without loss of yield potential.