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Catherina Cunnane
Catherina Cunnane
Catherina Cunnane hails from a sixth-generation drystock and specialised pedigree suckler enterprise in Co. Mayo. She currently holds the positions of editor and general manager at That's Farming, having joined the firm during its start-up phase in 2015.
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The ‘forgotten fertiliser’ on Irish farms

According to Mark Plunkett, Teagasc Johnstown Castle, lime is most definitely the forgotten fertiliser on Irish farms.

Irish farmers are currently only applying 50% of the country’s national requirements. In addition, 80 to 85% of soils are testing sub-optimal for major nutrients such as soil pH P & K.

Plunkett believes lime will be a key technology in the toolbox to increase sustainability on farms. Furthermore, he said it will help to meet new environmental targets set out in the EU Green Deal and the Farm to Fork and Biodiversity strategies.

Efficient N use, he pointed out, starts with correcting soil pH. For example, Irish farmers a double N efficiency by correcting soil fertility (pH, P & K), thus reducing fertiliser N use and reducing costs.

Changes in the timing of applications required

Traditionally, the back end of the year, i.e., October, November, and December, was the main period for applying lime.

On average, over the last five years, these months have been the wettest, as 30% of our annual rainfall comes at this time of the year.

“Waiting until the late season to apply lime will, generally, result poorer and less trafficable soil conditions, and the opportunity to apply lime could be missed.”

“Therefore, aim to apply lime earlier in the year when soil and weather condition are move favourable.”

“We can capitalise on the benefits of liming to use N more efficiently and to help reduce the total farm N requirements while at the same time protecting the environment.”

According to Plunkett, when it comes to applying lime, farmers must take every opportunity during the growing season. “Lime can be spread any day of the year provided soil and weather conditions are suitable.”

Apply ground limestone to Irish soils

He has produced a new factsheet on lime answers several common questions /myths when it comes to applying ground limestone to Irish soils, as follows:

1 – Paddock availability

Once fields have been grazed off and grass covers are low, it is ideal to apply lime.
Identify blocks of land that require lime.

For example, this could require ordering a load of lime (20t) after each grazing rotation to correct soil pH (covers approx. 10 ac @ 2t/ac lime application rate). Aim to avoid high grass covers > 800kg DM/ha.

2 – Residue on grass

Ideally, apply lime to low grass covers to reduce the risk of residues. Rainfall will typically wash most of the lime from the grass down to the soil.

Where a small amount remains on the leaf will not affect grazing animals. Grass covers on farms tend to be the lowest (500kg DM/ha) during April and August (PastureBase Ireland (PBI)) and presents good timing for application.

3 – Softening of the ground/sod

Soil types where a relatively thick (5-10cm) organic layer has formed above the topsoil may be more prone to poaching during the year’s wetter period. This organic layer holds a large store of acidity.

Liming these soils to neutralise acidity and raise pH will create favourable conditions for biological activity (e.g. grassroots, earthworms, ect) and the release of the nutrients stored in the organic matter.

As nutrients are released from organic matter, the resistance of the top few centimetres of soil to heavy trafficking may be temporarily reduced. To minimise these effects, apply on ‘a little and often basis’ and improve soil pH in stages over time.

Furthermore, do not exceed 5t/ha in a single application or apply split applications (2.5t/ ha) over a number of years.

4 – Silage fields

Leave sufficient time (up to 3 months in dry weather) between applying lime and closing for grass silage for the lime to be fully washed into the soil.

If lime is transported to the silage clamp or picked up in the baled silage, it may affect good preservation conditions for the silage (acidic conditions).

5 – Lime & slurry

Spreading cattle slurry on fields that have received lime recently or freshly limed land, where the lime has not had sufficient time or rainfall to be washed into the soil, can result in a loss of up to 50% of the available slurry N.

To minimise these N losses from slurry, apply cattle slurry first. Then, apply lime 7 to 10 days later.

6 – Lime & urea

For urea, a similar situation to cattle slurry where increased N loss (ammonia-N volatilisation) may occur where straight urea fertiliser is applied on recently limed land.

Therefore, apply urea first and apply the lime 7 to 10 days later to reduce the risk of N losses.

However, where protected urea is being applied, early trial work indicates that it is safe to apply protected urea to fields that have been limed recently.

7 – Lime & high Molybdenum soils

Soils with high Mo status may increase the risk of inducing a copper deficiency in grazing animals.

On these soils, increasing soil pH above pH 6.2 increases Mo’s availability in the soil and higher uptake of Mo by actively growing grass.

Where farms are affected by high Mo soils, maintain soils at or below soil pH 6.1 – 6.2. Alternatively, apply as recommended and supplement animals with copper.

8 – Speed of reactivity

Once lime is applied and is washed in, it starts to adjust soil pH. At least 35% of ground limestone (350 kg/tonne) has a particle size < 0.15mm.

This component is fast-acting and very reactive and will start working immediately (0-6 months).

The remaining 65% lime (650 kg/tonne) will be broken down in the soil in the medium term (6-24 months). This helps to maintain soil pH levels in the longer-term until the soils are re-sampled in year 4-5.

9 – Return on investment (ROI)

Research shows that liming acidic soils increases grass production by 1.0t DM/ha. On a drystock farm, this is valued at €105/tonne DM and €180/t DM on a dairy farm.

An application of 5t/ha of ground limestone to correct soil pH represents a cost of €25/ha/year over five years.

The return on investment from lime gives €4 to €7 worth extra grass for every €1 invested in lime.

10 – Type

Two main types of ground limestone are available nationally – calcium & magnesium. calcium lime is most widely available, while magnesium is mainly available in the southeast.

For more farming tips and advice, click here.

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