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Use of CAN and Urea for Early Grass Production

When deciding whether to use a Urea or CAN (Calcium Ammonium Nitrate) product, multiple factors should be taken into consideration such as economic, climatic and environmental.

Nationally, CAN sales are five times the volume of Urea sales with national Urea sales in the region of 115000 tonnes, however, the importance of Urea is increasing in recent years, especially for early grass production. Urea is a perfect source of Nitrogen at this time of year with limited losses. On a per unit basis Urea is 20% cheaper than CAN and can provide significant savings. Care is necessary when spreading Urea as it is 80% the bulk density of other products like CAN and so will have a narrower bout width, it is wise to set the spreader correctly and do your tray tests.

Urea Application

Urea goes through three steps before being available to the plant. Firstly, the Urea goes to Ammonia by hydrolysis and undergoes a conversion to Ammonium. This Ammonium is converted to Nitrate via Nitrite. Plants can utilise Ammonium and Nitrate but under normal Irish soil conditions it converts to Nitrate before grass uptake.

The reaction time for conversion to ammonium depends on temperature and soil conditions but typically reaction will begin to occur around 24 hours after initial application and will be complete within 3–7 days, but this reaction time is slowest in cooler, waterlogged soils.

When Urea is applied in unfavourable conditions to bare pastures or in windy conditions research has shown it is subject to losses due to volatilisation, therefore it is critical to have rain forecast just after or during application to ensure good soil incorporation to reduce these losses.

It is best practice to spread Urea with 7 – 10 mm of rain forecast within the following 2 days. Urea undergoes hydrolysis after its incorporation within 3 – 7 days. Urea is then converted to ammonia and this has to be nitrified to convert to nitrate before it can be utilised by the plant.

Depending on soil temperature this can vary as you can see in the table below:

Conversion of ammonium to Nitrate

This Nitrate is easily leached from the soil as it is negatively charged and is not held by the negatively charged soil particles or soil organic matter.

Target Fertilisers have developed products that will slow down the conversion of Urea to Ammonium and thus reduce ammonia loss by 80% and this comes in the form of an inhibitor called NBPT which is liquid coated onto the Urea granule marketed as Targets “UREAMAX + S”.

Target Urea Products:

  1. 46% Urea – This is the standard Granular Urea supplying the single nutrient Nitrogen
  2. 40% Urea + 6% S – This is for use where you have a Sulphur requirement. Amino acids are the building blocks of protein and two of them contain sulphur. The supply of S is therefore critical to optimise the efficient use of N.   It is good practice to apply N & S in a ratio of 12:1 across the season.
  3. Ureamax + S (40% N; 6%S + NBPT) – This was produced by Target Fertilisers in the response for the need to reduce GHG’s. Changing from CAN use to Urea reduces the Green House Gas, Nitrous Oxide but increases Ammonia emissions. These ammonia emissions can be reduced by up to 80% by using NBPT.   N-Protect B (NBPT) is a Urease inhibitor and has an active ingredient N- (n-butyl) thiophosphoric triamide. It protects the Urea from the urease enzyme, thus slowing down the process of the transfer of Urea to Ammonium and thus reduces the incidence of Ammonia volatilisation


Expert’s Recommendation:   Early Nitrogen for grass is max. 30 Kg/Ha

To learn more about nitrogen application for early grass production, read our previous blog post

To learn more about Target Fertiliser’s product range, click here

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