How effective is protected urea in grassland swards?

Protected urea is urea nitrogen (N) fertiliser made safe from ammonia loss through the addition of a urease inhibitor.

Despite the fact that protected urea can grow more grass than either calcium ammonium nitrate (CAN) or urea, it can also give the quickest reductions in greenhouse gas (GHG) and ammonia emissions within agriculture.

With the unpredictability in weather, the price of fertiliser, and the new constraints around how much fertiliser you can use, choosing the most effective fertiliser has never been more important.

With the introduction of the National Fertiliser Database (NFD), farmers had to complete a closing stock of fertiliser left on the farm on September 14, and had a month after that date to submit these records online.

Co-ops have to make regular returns to the database of the herd numbers that bought fertiliser, the date, type and amount of fertiliser purchased.

This monitoring and data collection has raised concerns amongst farmers who fear the possibility of exceeding their fertiliser limits.

With this in mind, it is important for farmers to understand the role of protected urea, understand their fertiliser limits and what to apply to allow for maximum growth.

Grass growth

In short-term Teagasc trials, the quantity of grass grown by using CAN, protected urea and urea was similar across all fertiliser types.

However, protected urea grew 13% more grass on average compared to standard urea in a long-term trial at Johnstown Castle, Co. Wexford. In the same trial, CAN yielded 9% more than standard urea.

From the trial illustrated above, protected urea and CAN had greater responses in growth rates in six out of the seven years of the trial, with 2018 being the exception due to drought when water was the limiting factor not nitrogen. 

The cost of protected urea

Protected urea is cheaper than CAN per kg of N, and it is more expensive than standard urea (on a per tonne basis).

However, it will give the same effective N for the plant as standard urea, at a 12% lower spreading rate as N losses from standard urea are significantly higher.

Protected urea is the cheapest option. The value of retaining N that had previously been lost as urea has increased substantially with increasing fertiliser costs.

Also with the new NFD and limits on N usage, it makes more sense to use less of a more effective product.

The relative cost of an application of N using different fertiliser types has been provided by Teagasc, as follows:

The reason for 57kg N/spread of standard urea is because it is the equivalent quantity of N needed to achieve the same plant available N, allowing for the extra losses with standard urea.

As a general rule of thumb, there is the same of amount of N in three tonnes of protected urea (46%) as there is in five tonnes of CAN (27%).

Based on February 2024 figures, three tonnes of protected urea will cost €1,650, while five tonnes of CAN will cost approximately €1,940 for the same amount of actual N.

Protected urea has been calculated to have 71% lower nitrous oxide emissions than CAN, proving that it has a key role to play nationally in terms of being an easy strategy of reducing GHG emissions.

By using protected urea, you will be contributing to the ammonia reduction targets for agriculture as it significantly reduces the calculated ammonia emissions by 78% compared to straight urea.

Application

Farmers can use protected urea from January to early September, which is a big advantage of the fertiliser.

The fertiliser is most effective in the spring time during damp conditions – during the summer months, it releases N slower and more effectively than CAN due to the inclusion of the urease inhibitor.

Due to the higher N content, the application rate will be lower than CAN and the fertiliser density is also lower for urea fertiliser versus CAN, which makes it more difficult to spread at wider bout widths.

However, larger and stronger granules indicate that fertiliser is of better quality. Protected urea has the potential to draw more moisture which can lead to issues with your spreader if it is not washed out properly after use.

It is important before you spread any form of fertiliser, that you set the spreader accordingly to match the fertiliser’s quality on the spreader manufacturer’s database which will assess size and strenght.

You can use the manufacturer’s app to determine the bout or width capabilty and the spreader settings from disc vane to hopper height and angle to ensure accurate spreading.