Teagasc research has shown that every 1kg/ha nitrogen (N) applied in early spring (February and early March) produces in the region of 10kg DM/ha of grass.

This additional grass can be a significant saving if it can be utilised on the farm.

Urea-based N fertiliser is typically the product of choice for early season application in order to maximise nitrogen use efficiency (NUE), especially where soils have an adequate pH level greater than or equal to 6.3.

Urea conversion process

Urea goes through three conversion steps when applied to the soil. Urea first converts to ammonium through hydrolysis and the action of the urease enzyme. This ammonium can be quickly converted to nitrates through the action of nitrifying bacteria in soil.

Plants can utilise both ammonium and nitrate but under Irish soil conditions, conversion and uptake of nitrate-N forms is dominant. This nitrate can be more easily leached from the soil as it is negatively charged and is repelled by the negatively charged soil particles or soil organic matter.

The time for urea to be converted to ammonium depends on temperature and soil conditions but, typically, reaction will begin to occur within 24 hours after application and will be complete within three to seven days. This conversion is slowest in cooler, waterlogged soils and faster when soils dry out and begin to warm up from late spring onwards.

When urea is applied in unfavourable conditions such as to bare pastures or in windy and drying soil conditions, research has shown it is subject to increased N losses due to volatilisation.

It is best practice to spread urea in late spring and summer when 7mm to 10mm of rain is forecast within the following two days as this will ensure good soil incorporation, and help to reduce these losses.

Alternatively protected urea can be used anytime during the growing season.

Protected urea/urease inhibitors

To reduce ammonia emissions, urea-based fertilisers can be treated with a urease inhibitor, namely NBPT, NPPT or 2-NPT.

Urea treated with these urease inhibitors are called protected urea products and offer a cost-effective solution to reducing emissions. These inhibitors slow the transfer process of the urea to ammonium, reducing ammonia losses by up to 79%.

They increase the duration of N fertiliser supply in the soil for plant uptake between fertiliser application. This urease inhibitor concentrate is sprayed on to the urea granules, giving protection to each and every granule.

There are a number of products/ranges available from Irish fertiliser suppliers.

There is a list available from the Department of Agriculture to show approved urease inhibitor products. These are also approved/trialled by Teagasc.

Inevitably, these products will contribute to lowering greenhouse gas emissions and ammonia losses, thus helping meet Ireland’s 2030 emission targets.

Urea spreading and calibration

It is important firstly to understand the importance of fertiliser granule density and its effect on application spread patterns and distance travelled. Granule density is the mass to volume ratio of granules. This is a measure of the physical weight of one litre of fertiliser by a weighting scale.

Urea fertiliser granules have lower density which is 25% less than calcium ammonium nitrate (CAN). Urea is 0.75kg/litre compared with CAN at 1kg/litre.

Fertiliser density has a large impact on the spreading distances of both products

The denser fertiliser granules will spread wider at high spinning disc speeds.

It is important to check fertiliser spreader manufacturers’ spreading calibration setup for specific products and subsequently carry out a tray test.

It is not recommended to spread urea products on bout widths exceeding 24m, even in ideal conditions.