Spreading slurry? Here’s how long you need to wait before applying urea

Farmers spreading urea and slurry at this time of year need to spread out the time between each application, according to Teagasc’s Mike Egan.

Egan spoke at a recent Teagasc Spring Grazing Farm Walk in Banagher Co. Offaly, where he said farmers should leave seven days between slurry and urea spreading.

Farmers should spread slurry first, he said, to allow the slurry to absorb into the ground first and to avoid covering the urea granule with slurry.

“The problem with spreading slurry after urea is that the slurry coats the urea granules and stops it from working.

“It ties up the Nitrogen in the urea and makes it unavailable to the grass.

“Urea needs oxygen to work and if the slurry is spread after urea it reduces the N available to the grass from the urea,” he said.

The Teagasc Post Doctoral Researcher said that farmers should aim to spread slurry before urea at a rate of 3,000 gallons/ac on grazed ground.

Teagasc research shows that slurry is a carbon source and when it is spread directly after slurry it results in the loss of N. This is the case for both urea and Calcium Ammonium Nitrate (CAN).

He also recommended spreading slurry in the spring time, as this is when grass can use the N content of slurry in the best way.

1,000 gallons of slurry/ac will provide six units of N, this can reduce the amount of urea or CAN needed.

Teagasc research shows that the cool temperatures in the spring are the best time to apply slurry, as N is lost to the atmosphere during warm sunny weather in the summer time.

Soil temperatures should reach six degrees Celsius before farmers spread slurry. Once the soil reaches this temperature grass starts to grow and use N, it shows.

Teagasc's Mike Egan speaking at the farm walk.
Teagasc’s Mike Egan speaking at the farm walk.

Another factor Egan said needed to be considered was the amount of time between slurry spreading and grazing.

“Farmers need to leave six weeks between slurry applications and grazing to avoid cows turning their noses up at soured grass.

“The length of time can be reduced by two weeks if a trailing shoe is used, as the slurry is placed directly onto the soil and not the leaf,” he said.

Spring fertiliser applications

Egan also spoke about Nitrogen applications this spring and he recommended that farmers stick with urea.

The Teagasc representative said that farmers should aim to spread 70 units of N/ac by April 10 and this application should be split in two (half a bag and a full bag of urea two weeks apart).

He said that spring fertiliser applications are important to maintain the covers of grass on paddocks and to stop them disappearing with the cold harsh weather.

“Holding the herbage on the paddocks is important. Farmers might not be getting a huge response to N at the moment.

“Growth rates are slower this spring due to the frost at night. The typical response from one unit of N applied in the March is 15kg of grass dry matter/ha, but it has not reached these levels yet,” he said.

Work carried out in Teagasc Johnstown Castle shows there is no difference in the amount of grass grown from either urea or CAN applications in the spring, but urea is a lot cheaper to apply.