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Preparing to get nitrogen applications back on track

Preparing to get nitrogen applications back on track

Along with the associated grazing challenges, the wet spring has limited the opportunities for both organic and artificial fertiliser applications on many farms.

With limited quantities spread, and suggestions from industry that just 25% of normal fertiliser volumes have been sold up to the beginning of April, how farmers react and adjust their fertiliser spreading strategy will have an impact on the availability of grass and re-growth rates once weather and ground conditions finally permit an uninterrupted grazing season.

As part of the recent ‘Managing the herd in current weather conditions’ webinar, Dr Michael Egan, Grassland Research Officer in Teagasc Moorepark, presented a number of scenarios that dairy farmers may well find themselves in terms of spring nitrogen applications to date and the most suitable pathway to follow in each instance.

Before the most appropriate nitrogen fertilisation strategy can be selected, Michael advised that fertiliser should only be spread when conditions allow – that being soil temperatures above 6 degrees Celsius, to non-water logged soils and to avoid spreading in the 24-48 hour period in advance of a forecast heavy rainfall event.

He also reminded farmers who are planning to spread once conditions permit to source supplies now, adding: “Talking to any of the fertiliser reps, there is very little fertiliser sold or moving. If you have not got fertiliser bought, try and put in an order for it straight away because there is going to be huge delays if weather takes up with the tillage sector and the dairy sector trying to get fertiliser in yards with restrictions in terms of lorry haulage and feed mills being extremely busy.”

Scenario one – applications up to date

As part of the webinar, Michael outlined four different fertiliser strategies. Presented in table 1 below, these include: (1) up to date on fertiliser applications; (2) one round of fertiliser out; (3) slurry only spread; and (4) nothing spread.

For farmers in scenario one, where >70kg/ha of nitrogen has been applied and grazing is more than likely occurring when the opportunities present, Michael recommended applying 15-20kg/ha of nitrogen after each grazing event.

Scenario two – one round of fertiliser out

The second scenario, a position many farmers may find themselves in, is where one round of nitrogen of approximately 30kg/ha has been applied. For such farms, the aim is to get nitrogen applications up to the target of 70kg/ha by allowing four weeks to elapse between the previous application and then applying 30-35kg/ha of nitrogen before reverting to following the cows after grazing.

“Depending when it went out in March, try and leave a window of four to five weeks before your second application. Ideally if it was March 15, target April 15 for your second round,” Michael said.

Scenario three – slurry only

The third scenario highlighted by Michael related to farms that only applied 2,500 gallons/ac of slurry in January/February, but as of yet have yet to apply artificial nitrogen.

For these farms, Michael recommended: “Blanket spread everything as soon as conditions allow with something in the region of a bag of urea or a little under (~40kg/ha of nitrogen), depending on the cover of grass that you have and how much slurry and when the slurry went out.”

Scenario 4 – no slurry or fertiliser applied

The final scenario discussed related to farms where neither slurry nor artificial nitrogen has been applied. For these farms, Michael advised them to blanket spread with ~40kg/ha of nitrogen as soon as conditions allow.

“If there is no slurry out, apply your slurry after grazing. Prioritise chemical nitrogen over the slurry at this stage just because of trafficability issues unless it is a pipe that is going out,” he said.

Farmers in this scenario may be tempted to delay nitrogen applications until the paddocks have been grazed, but Michael argued that applying before grazing will be beneficial for re-growths following grazing, adding: “Try to spread everything at this stage unless the cows are currently in it. I think we are in a situation now where we need to get grass growing. It (grass growth) has been reasonably good but, with very little grazing done, re-growths are going to be hit and by not spreading those paddocks now, it is going to delay them further.”

Although some of these paddocks may have heavier covers, leading to a butt once grazed, he noted that failing to apply nitrogen to such paddocks will further delay regrowths by between five and 10 days.

Table 1: Fertilsier for grazing

 Scenario 1Scenario 2Scenario 3Scenario 4
  Up to date One round of fertiliser out Slurry only spread Nothing spread
Volume spread  +70kg/ha of nitrogen spread ~30kg/ha of nitrogen spread (March) ~2,500 gallons/ac (Jan/Feb) -
Advice Continue to follow cows after grazing Allow four weeks between applications - ~30kg/ha of nitrogen Blanket spread ~40kg/ha of nitrogen when conditions allow

Blanket spread ~40kg/ha of nitrogen when conditions allow

Apply slurry after grazing at a rate of 2,000 gallons/ac

The role of phosphorous

On account of regulation change, there is a heightened need for farmers to be fully aware of the phosphorous (P) allowances available to them to ensure they remain complaint. However, where farmers have an allowance to apply chemical P, Michael highlighted the key areas to where it should be targeted. He noted that it should be targeted at paddocks, with a potential requirement for P, which may have been damaged during early grazing this year to encourage tillering and to avoid the ingression of weeds. Where farmers have no chemical P allowance, slurry spread at a rate of 2,000 gallons/ac should be applied to provide such paddocks with P.

To see Michael’s full presentation, re-watch the webinar here.

Also read: Fertilising first cut silage crops - correct application ensures correct cutting date

Also read: Learnings from Ballyhaise - managing through a difficult spring