In Ireland, about 60% of soils on dry stock farms are sub-optimal for lime, approximately 40% of soils on dairy farms and about 40% of tillage soils are sub-optimal.

In Ireland, about 1m tonnes of lime is spread per year, Mark Plunkett training and development specialist with the Teagasc signpost programme told the Irish Farmers Journal at the 'Farming for a Better Future' open day at Teagasc Johnstown Castle in Co Wexford on Wednesday.

However, he estimated that another 0.5-0.75m tonnes of lime should be spread annually to meet the desired requirements.

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This would help contribute to optimal soil pH. For example, in grassland soils, the optimal pH range is 6.3 to 6.5 and tillage soils have a slightly higher optimal pH range of 6.5 to 6.8, he said.

Lime usage in Ireland has increased over recent years, but Plunkett added that more lime is still required on many farms in Ireland, especially on the grassland side and dry stock farms.

“The soil test results are saying that about 64% of dry stock farms need lime,” he said.

Lime application rates range from 5 to 7.5 t/ha with 5t/ha (2t/ac) being the typical application rate. This costs €175/ha or €70/ac and when costed over five years, it represents a lime maintenance cost of €14/ac/yr.

Small investment

This small investment of €14/ac per year in lime can deliver significant production, economic and environmental benefits.

Having soils at optimum pH ensures that nutrients applied (N and P) to crops are utilised by the growing plant efficiently, reducing the risk of nutrient loss to waters.

In terms of nitrogen, getting soil pH to that sweet spot can help to mineralise about 70kg of nitrogen per hectare per year, coming from the soil organic matter.

As a result, this can help reduce chemical fertiliser use, increase grass production and productivity and also increase the availability of soil phosphorous.

Correcting mineral soil pH levels to the optimal range can increase grass production by up to 2.5t DM/ha/year.

This is worth €17,000 in extra grass production on a 100-cow dairy farm or €10,500 on a 40-cow suckler farm.

Soil phosphorous

“Here today we're saying that by getting the pH up from say, a pH of 5.5 up to 6.3, we can improve the soil P by an index,” Plunkett outlined.

“If we were to do that with bag fertiliser, we're talking about 150kg of phosphorus, and that's something like 1.5t of 10-10-20.”

Plunkett recommended that before trying to improve the soil phosphorus through chemical fertiliser, farmers should be getting the soil pH right to improve both the soil supply and the efficiency of either the nitrogen, phosphorus or the potassium that is applied on an annual basis, reducing the use of chemical fertilisers.

He highlighted that with recent volatility and price increases in the fertiliser sector, it is essential to get the soil pH correct with the use of lime, so that fertiliser can be used more efficiently and to get more out of the soil whether it's crops, grass production or animal health.