Do urea-based fertilisers have a role in malting barley?

With high fertiliser prices continuing into early 2023, Dr. Richie Hackett of Teagasc Oak Park outlined the benefits and potential drawbacks of using urea-based fertilisers when growing malting barley.

Addressing the recent Teagasc National Malting Barley Conference, he explained that there are economic benefits of making the switch from CAN to urea-based fertilisers. Using market prices from earlier this year, he said, a 40ha farm could make savings of €5,000 when moving from more traditional type CAN products to urea products this year, when application rates are at 150kg of N/ha.

“Probably the big benefit of urea at the minute is the cost. It is also a more concentrated form of nitrogen. If you fill your fertiliser spreader full of urea versus CAN you will have more kilograms of nitrogen in your spreader.”

Presenting previous research, which examined the impact of CAN, urea and protected urea on malting barley yield and protein, he said: “Protected urea is a good option for tillage. It gives comparable yields on a consistent basis. It is comparable in terms of protein also.”

CAN-type fertiliser have been traditionally used in cereal and grassland situations in Ireland, but with legislative requirements to reduce greenhouse gas emissions from agriculture, Dr. Hackett pointed to the role that protected urea may play. Previous Teagasc research has shown that moving from CAN to protected urea reduces nitrous oxide emissions from grassland production systems. Although smaller, the same benefits exist for tillage.

Of course there are economic benefits of using unprotected urea in favour of CAN this year, but Dr. Hackett outlined chemical reactions that occur in the soil when unprotected urea is used that can potentially result in the loss of ammonia gases. This ammonia gas is generated during the breakdown of unprotected urea, which occurs relatively soon after application and can lead to the loss of a significant amount of nitrogen.

“One of the principal drawbacks of using [unprotected] urea is some of the nitrogen can be lost to the air as ammonia gas. When it’s lost to the air, it’s no good to the crop and it’s causing environmental issues," he explained.

To reduce this loss occurring, urease inhibitors are included in protected urea to slow down this chemical reaction. Urease is the enzyme which causes the breakdown of urea, making it available to the growing plant.

“When we talk about protected urea, we are slowing down this process. We are slowing down the release of gas and we are preventing the loss of nitrogen out of the soil and we are keeping it for the crop to use,” he explained.

Pointing to the risk factors that increase the potential for loss from unprotected urea, he explained: “Probably the worst case scenario is applying it to a moist soil, where the urea dissolves on the top of the soil. It’s not washed into the soil, it just dissolves on the surface and the soil starts to dry out. They are probably the high risk situations.

“High pH, particularly after liming, is also a risk factor. The advice is always, if you are going to apply urea, apply it before the lime rather than after the lime. High temperatures will tend to increase the loss as well. The risk can be a little bit higher on lighter soils than on heavier soils.”

On minimising the losses, he said: “If we can apply unprotected urea just before some light rain (10-15ml), that will reduce the loss of ammonia because it will dissolve the urea and wash it into the soil. These days the best way or the safest way to reduce the risk is to use protected urea.”

For farmers considering spreading urea-based fertilisers in 2023, he did offer a word of warning on the actual task of spreading the product accurately.

“Urea is less dense than CAN. It is a light product. It is more difficult to throw any distance. It is not that you can’t spread it, but it is more difficult to spread it at wider widths. If you are on 12 or 15m tramlines, you shouldn’t have any great difficulties, but once you start going up to wider trams, it becomes a bigger challenge to spread it evenly and once you go about 24m, you need to be really careful.”

Hackett also urged caution when using blends, particularly when fertilisers of different density or weight are being applied, as it increases the difficulty of achieving an even spread.

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