Liming acidic soils has been one of the biggest developments in Irish agriculture. to-date The first applications of lime to soils revolutionised agriculture and enabled more grass and lime-sensitive crops such as clover, beet, beans and cereals to be grown on farms.

Today, more than ever, the benefits of lime applications will be called on to protect soil productivity and help farmers meet new environmental targets set out in the EU Green Deal and in the National Climate Action plan.

Recent Teagasc research has proven that raising soil pH through liming can reduce greenhouse gas emissions (nitrous oxide) by up to 40% on grassland soils.

Lime use in Ireland

Over the last two years, sales of lime in Ireland have increased to greater than 1.2m tonnes compared to the last three decades (1990s, 2000s and 2010s), where, on average, only 700,000t of lime was applied annually.

In the 1970s and early 1980s, an average of 1.7m tonnes of ground limestone was applied annually. Lower liming rates on Irish farms have led to increased soil acidity, but in the last five years, improvements have been seen.

However, there is still very little lime applied in some regions of the country.

Currently, national soil test results indicate that 47% of dairy farm soils, 57% of drystock farm soils and 39% of tillage soils require lime to neutralise high soil acidity levels

Increased soil N supply with lime

Efficient nitrogen (N) use starts with correcting soil pH and we can double our N efficiency by correcting soil fertility (pH, P and K), thus reducing fertiliser N use and reducing costs. Soil testing is the best indicator of how much lime is needed to reach the target soil pH.

On mineral grassland soils, the target pH level is 6.3 and up to 6.8 on grass-clover swards. For tillage crops, there is a target soil pH of 6.5 for cereals and up to 6.8 for legumes and beet is required. Raising the soil pH on acidic soil will increase the supply of N from organic matter by up to 65kg/ha/ year. In effect, this means that farmers can reduce chemical N applications by this amount and grow the same amount of grass annually.

At current fertiliser prices, this offers a considerable cost saving (€160/ha) on the annual fertiliser bill for a farm.

Take every opportunity

When it comes to applying lime, we must take every opportunity during the growing season. Lime can be spread any day of the year provided soil and weather conditions suit. Traditionally, the back end of the year – ie October, November and December – was the main period for applying lime.

However, approximately 30% of our annual rainfall comes at this time of the year.

Waiting until the late season to apply lime will generally result in less trafficable soil conditions and the opportunity to apply lime could be missed. The following identifies a number of opportunities during the year to apply lime;

  • Grazing ground – Once fields have been grazed off, it is an ideal time to apply lime. Earmark blocks of land that needs lime based on a recent soil test report. For example, this could mean ordering a load of lime (25t) after each grazing rotation to correct soil pH. Avoid applying lime on to heavier grass covers (= 750kg DM/ha) as this will reduce the time available for the lime to wash off the grass and into the soil.
  • Silage fields – Ideally, leave less than eight weeks between applying lime and closing for grass silage. If it gets too late to apply lime to silage fields this spring, you should plan to apply lime once the silage has been cut, as fields will be bare and soil conditions should be good.
  • Lime and slurry – Spreading slurry on to fields that have received lime applications in recent weeks, and before the lime has had time to wash into the soil, can result in a loss of up to 50% of the N in the slurry.
  • In order to reduce the potential for increasing N losses from slurry, it is recommended to apply the slurry first and then apply the lime seven to 10 days later.

  • Lime and urea – A similar situation to the lime and slurry in relation to N loss. It is recommended to apply the urea first and apply the lime seven to 10 days later to reduce the risk of N losses.
  • Where protected urea is used early, trial work indicates that it is safe to apply protected urea to fields that have received lime recently.