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Growth Watch: Deadline approaches for nitrogen and phosphorous applications


James Fitzgerald & Séan Cummins, Teagasc GreenAcres Advisors, discuss the approaching deadline for applications of chemical nitrogen and phosphorous fertilisers. They also get updates from farmers Pat Collins, Co. Cork, and Irvine Allen, Co. Westmeath.

The Advice

As August turns to September, the deadline for applications of chemical nitrogen and phosphorous fertilisers is drawing closer.

The chemical fertiliser spreading closed period begins on September 15 for the entire country and so – from this date onwards – the spreading of chemical fertiliser containing phosphorus (P) or nitrogen (N) is prohibited.

Work carried out in Teagasc Johnstown Castle indicated that a 30kg/ha (24 unit/ac) application of N generated a growth response of 27kg DM/kg N in August and just under 20kg DM/kg N in September, with both applications taking place at the start of the respective months.

After a period of restricted growth on many farms, growth rates have bounced somewhat on farms participating in the Teagasc Green Acres Programme over the past two weeks. This has resulted in most farms not requiring a split of N for the rest of the year to achieve the maximum farm cover by mid-September.

However, there are some variations. Where farms are struggling to reach the 1,000kg DM/ha average farm cover target by mid-September – and where growth rates are lagging – a split of nitrogen may be justified when an allowance is available as part of the farm’s Nutrient Management Plan.

With ground conditions still holding relatively well on many farms and a fine spell of weather forecast, there is an opportunity to ensure slurry tanks are emptied before conditions deteriorate.

The application of slurry now will also provide the grass plant with nutrients such as nitrogen, phosphorous and potassium which will help to build grass covers going into the shoulders of the year.

Pat Collins, Castlemartyr, Co. Cork

  • Growth: 87kg DM/ha/day
  • Demand: 33kg DM/ha/day
  • Average farm cover: 771kg DM/ha
  • Stocking rate: 2.45LU/ha

Growth has really rebounded here over the past two weeks. A growth rate of 87kg DM/ha/day was recorded this week, while demand is running at 33kg DM/ha/day.

With bulls housed for finishing, the demand has dropped by about 66%. On account of this, I've reduced fertiliser applications significantly.

However, with conditions coming optimum for growth, excellent soil fertility and a high proportion of white clover in the grazing paddocks, the average farm cover here has risen by 270kg DM/ha in the space of two weeks.

With just 2021-born calves and early-maturing heifers remaining at grass, the demand here will remain relatively low until housing.

To ensure that quality grass is maintained ahead of stock at the optimum pre-grazing covers, I have removed six paddocks in the form of surplus bales this week.

It is getting a little late in the season to be taking surplus bales, but with good growth rates expected this week and a relatively low demand for grass, I will still have sufficient grass to reach the maximum farm cover in mid-September.

Irvine Allen, Moate, Co. Westmeath

  • Growth: 32kg DM/ha/day
  • Demand: 43kg DM/ha/day
  • Average farm cover: 950kg DM/ha
  • Stocking rate: 2.12LU/ha

Growth has really taken off over the past 10 days and corrective action needed to be taken. To counteract this and to maintain quality grass in front of stock, I have targeted five paddocks for surplus bales this week.

It will probably leave me a little tight in the short term, but if I hadn’t of taken this step now I would have too much grass in the next week or two.

By removing these paddocks now, it corrects the average farm cover to 950kg DM/ha and it brings me close to meeting my silage requirements for the winter months.

Half of the calves are receiving 1kg/head/day of concentrate, with older calves set to receive meal in mid-September prior to housing.

In terms of finishing stock, concentrates have been introduced to 25 steers, which are destined for slaughter in early to mid-November. As a group, these animals are in excess of 500kg.

A bag of 18:6:12 per acre was applied to the grazing ground at home 10 days ago as soil fertility is challenging here.

The Teagasc GreenAcres Programme Advisors have regular contributions here on Teagasc Daily. You might also like to keep up to date by signing up to their e-newsletter. Find out more about the Teagasc GreenAcres Calf to Beef Programme here.