Changing the timing of lime application

Lime is most definitely the forgotten fertiliser on Irish farms. Farmers are currently only spreading 50% of the national lime application required.

In addition, 80-85% of our soils are testing suboptimal for major nutrients such as soil pH, phosphorus and potassium. This is according to Mark Plunkett, a soil and plant nutrition specialist at Teagasc.

Mark stated that: ”Lime will be a key technology in the toolbox to increase sustainability on farms and will help to meet new environmental targets set out in the European Union (EU) Green Deal and the Farm to Fork and Biodiversity strategies.

”Efficient nitrogen (N) use starts with correcting soil pH. For example, we can double our N efficiency by correcting soil fertility (pH, phosphorus (P) and potassium (K)), thus reducing fertiliser N use and reducing costs.”

Changes in timing of lime application is required

Mark stated that the timing of lime application may need to be changed: ”Traditionally, the back end of the year; 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 [in] 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 conditions are move favourable,” he continued.

”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.”

Ten tips for lime application

1.Paddock availability

Once fields have been grazed-off and grass covers are low, it is an ideal time to apply lime.

Identify blocks of land that require lime; this could require ordering a load of lime (20t) after each grazing rotation to correct soil pH (covers approx. 10ac at 2t/ac lime application rate).

Aim to avoid high grass covers (> 800kg DM/ha).

2.Lime residue on grass

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

A small amount of lime remaining on the leaf will not affect grazing animals.

Grass covers on farms tend to be lowest (500kg DM/ha) during April and August (PastureBase Ireland (PBI)) and this presents good timing for lime 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 wetter periods of the year.

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 (grass roots, earth worms) 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 lime on “a little and often basis” and improve soil pH in stages over time. Don’t 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 three months in dry weather) between applying lime and closing for grass silage in order 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 and 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 nitrogen (N).

To minimise these N losses from slurry apply cattle slurry first and then apply the lime 7-10 days later.

6.Lime and Urea

For urea, a similar situation to cattle slurry, 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 7-10 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 and high molybdenum soils

Soils with high molybdenum (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 the availability of Mo 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 lime 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/t) has a particle size <0.15mm.

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

The remaining 65% of lime (650 kg/t) will be broken down in the soil in the medium-term (6-24 months) and helps to maintain soil pH levels in the longer-term, until the soils are resampled in year four to five.

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/t 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 an extra €4-7 for every €1 invested in lime.