27 May 2025

Don’t miss the opportunity to apply lime

When it comes to applying lime, farmers have been encouraged to take every opportunity to do so during the growing season, Specialist on the Teagasc Signpost Programme, Mark Plunkett reminds us of the key benefits of liming.

To maximise the return from applied fertilisers, soil pH must be maintained in the optimum zone through the regular application of lime based on up-to-date soil test results. 

Optimising soil pH will increase the soil supply of nitrogen (N), phosphorus (P) and potassium (K) at least cost. In addition, it will increase the efficiency/uptake of nutrients such as applied organic (cattle slurry) or chemical fertilisers (protected urea, 18-6-12 etc.).

Soil N supply

Liming acidic mineral soils to the optimum pH 6.3 to 6.5 will result in the soil N supply increasing by up to 80kg of N/ha/year. This will increase farm N supply and support grass growth during the growing season, while controlling fertiliser N costs by ~€110/ha (€45/ac) per year.

Nitrogen Use Efficiency (NUE)

Maintaining optimum soil fertility increases the efficiency of applied N from 35% on low fertility fields to 63% on fields with optimum pH, P and K (see figure 1 below).

Correcting soil pH alone will result in an improvement in N efficiency from 35 to 53% where soil P and K is sub-optimal (see figure 1). 

With tighter fertiliser N legislative limits, spending money on lime to correct soil pH will ensure a better return from each kilo of N applied. For example, for every 100kg N/ha applied, the available N increases from 35 to 53kgN/ha from correcting soil pH to the optimum soil pH alone.

Figure 1: Percentage NUE and grass growth response to N fertiliser across grassland fields according to the status of soil pH, phosphorus (P) and potassium (K) fertility

Soil P availability

Correcting the soil pH increases the availability of soil P and the utilisation of P as either cattle slurry or chemical P fertiliser by the growing crop. A study completed at Johnstown Castle demonstrates how critical lime application can be for increasing soil P availability (see figure 2 below). 

For example, liming an acidic soil (pH<5.5) alone increased the soil P by ~6mg/l (2 Soil P Indexes). On many farms, this would remove the need for building soil P levels and increases the productivity (+ 1 tonne dry matter/ha) of the grass sward at least cost. 

With P being the most expensive nutrient in a more regulated environment, maintaining optimum soil pH pays many dividends for farm productivity and profitability.

Figure 2: Average change in soil test P (Morgan’s P test) across 16 mineral soils treated with P (100 kg/ha of P), Lime (5 t/ha of lime), and P + Lime and re-tested after 12 months (Sheils, T., et al, 2013)

Clover requires higher soil pH levels

Recent trial work from Johnstown Castle shows that by increasing soil pH from 5.5 to 6.8, the productivity of grass-clover swards for a lower input of chemical N increases (see figure 3 below). To boost clover productivity and the N-fixing ability of existing clover swards, aim to maintain higher soil pH 6.8. Where grass clover swards are being established, aim to correct soil pH, P and K levels in advance of reseeding to ensure fast, successful clover establishment and sward longevity.

Figure 3: Effect of soil pH on the productivity of grass clover swards

When and where to apply lime?

Grazing ground

Once fields have been grazed off, it is an ideal time to apply lime. Earmark blocks of land that need lime based on a recent soil test report. For example, this could mean ordering a load of lime (20 or 25t) after each grazing rotation to correct soil pH.

This could be done on number of occasions over the coming months, as soil and weather conditions are more favourable. This will not impact on grazing animals, as the lime will be applied to low grass covers. Even in the event where a small amount of lime remains on the leaf, it will not affect grazing animals.

Silage fields

With earlier silage harvests in 2025, now is a good time to apply lime to these fields where a second cut is not planned. Check soil pH levels and plan lime applications over the coming weeks.

Lime and slurry

Leave three months between the application of lime and cattle slurry to reduce the risk of losing up to 50% of the N.  Alternatively, to reduce N losses from slurry, it is recommended to apply the cattle slurry first and then apply the lime 7 to 10 days later.

For more tips and advice of applying lime, view the Signpost Programme’s guide (PDF) here.