The inclement weather and particularly high rainfall levels experienced in the winter months have delayed fieldwork this spring. There have been very few opportunities for farmers to get slurry or farmyard manure applied early in the season, while reports indicate that very low levels of chemical fertiliser have been applied to-date.

Despite this situation, winter grass growth has been relatively good with above normal temperatures sustaining a low level of growth.

Philip Creighton, Sheep Enterprise Leader at the Animal & Grassland Research and Innovation Centre, Mellows Campus Athenry, notes that some of this growth was boosted by swards utilising residual nitrogen available, which in many cases has now been depleted.

This is showing in recent weeks with grass growth rates stagnant when normally there should be upward momentum at this time of year.

The aim now for sheep farmers is to avail of any opportunity that presents itself to get fertiliser applied, says Philip.

“While growth has been reasonably good and opening covers are for many on target or close to target levels, grass reserves will be quickly depleted and sward recovery times reduced without applied nutrients to replenish fertility. Rain again this week and lambing commencing are presenting challenges but it is important that any opportunity to apply nitrogen is taken.”

Application rates

Table 1 (see below) details Teagasc advice for applying nitrogen fertiliser based on stocking rate and also outlines suggested application dates to ensure sufficient grass is available. This is based on typical grass growth rates across the grass growing season.

The advice for highly stocked enterprises with a stocking rate of upwards of 12 ewes/ha is 25kg N/ha (20 units per acre) in February / March, rising to over 30kg/ha (24 units/acre) for flocks stocked at 14 ewes/ha.

These systems will be under the greatest pressure for grass and as such the urgency to apply nitrogen is at its highest level.

The ideal scenario is where fertiliser can be blanket spread across the farm. Where this is not possible due to, for example, unsuitable ground conditions, there is even greater merit in targeting areas where fertiliser can be applied. Likewise, the optimum situation is where fertiliser is applied to swards with a cover of grass and organic manures to grazed swards.

Lowly stocked farms are under slightly less pressure to get fertiliser applied, but a March application is still warranted. The recommended application rates are also based on swards being closed in adequate time in 2023.

Where grass supplies are running behind target then this needs to be factored in to the equation when selecting the most appropriate application rate.

Targeted applications

Fertiliser prices have reduced somewhat after record prices in recent years. Teagasc advice during this period was to focus on applying nitrogen fertiliser if possible – the aim was to limit expenditure on fertiliser but still sustain grass growth.

This advice concerned fertiliser applications on lands where soil fertility and soil pH were at adequate levels and where strategic use could be made of organic fertiliser applications to target phosphorus (P) and potassium (K).

This approach has in some cases led to soil fertility being depleted, and the focus should now be returning to addressing soil fertility.

Philip says that spring fertiliser applications will still, in the main, be dominated by applications of straight nitrogen products, but he advises that greater attention may need to be placed on the use of compound fertilisers in April and May.

“We need to be realistic about the challenges that have faced farmers in recent years in terms of input costs. The overall approach needs to remain on tackling the areas that can deliver the best return. Recent soil analysis information is the starting point.

“Then we need to prioritise lime application to deliver the right soil conditions and then focus on getting the most from the nutrients inside the farm gate and the areas that deliver the greatest response.”

He adds that opportunities for applying slurry or farmyard manure have been limited, but stressed that this should not alter the focus on using these strategically to address soil fertility issues and also to replenish fertility where significant offtakes will be removed through silage / hay.

The approach in 2024 will likely be to continue to work on the areas that deliver the best response for your investment and expanding from this as finances allow.

Teagasc advice majors on the use of protected urea over urea/CAN. Table 2 (see below) details the fertiliser plan for the research demonstration flocks currently being examined in the clover trial in Athenry. The flocks are stocked at 10 to 11 ewes per hectare.

Taking stock

The advice for producers is also to get out and walk closed fields to ascertain what grass is available and to allow plans to be put in place. The target average farm cover for March lambing flocks is in the region of 600kg DM/ha to 650kg DM/ha.

Knowing the volume of grass present in a paddock and the weekly growth rate are invaluable tools for managing grass. For example, in early lactation a ewe’s intake is approximately 2.4kg DM/ha to 2.5kg DM per day.

This increases for a twin suckling ewe to 3.2kg DM in week five and 3.4kg DM in week seven of lactation and eases off thereafter following peak milk. From here until weaning it remains pretty static.

Knowing the volume of grass in a field and the growth rate will allow farmers to budget grass supplies to demand. For example if we take 10 ewes grazing with a grass demand of 2.5kg DM/ha, daily demand is 25kg DM.

Take a paddock with 7cm grass height on average across a sward or 1,050kg DM/ha there is enough grazing in theory for 42 days, or for 50 ewes there is just over eight days grazing without taking current growth into account.

If grass supplies are running behind target and there are challenges in getting fertiliser applied then the next task may be to consider supplementing ewes in early lactation to conserve supplies.

Fertiliser application tips

  • Tailor application rates to feed demands, and target areas that will deliver the greatest response.
  • The minimum soil temperature required for growth is 6oC. The majority of soils are above this level presently.

  • Base fertiliser applications on recent soil analysis.
  • Correcting soil pH through the application of lime will release N, P and K tied up in the soil.
  • Refrain from applying fertiliser on wet soils as it will result in possible nitrogen loss and soil damage. Do not apply organic or inorganic fertilisers within 48 hours of heavy rainfall forecast.
  • Young swards with a high perennial ryegrass content and fields with a grass cover (5cms or above) should be prioritised for chemical fertiliser application. Fields with lower grass covers should be targeted where feasible for slurry/farmyard manure.