Turning to lime to reduce costs for dairy farmers

Irish Teagasc advisor, Marion Fox, says farmers need to turn to lime to help reduce fertiliser costs, but at the same time boost soil fertility. Lime is very cheap when compared to fertiliser, costing around €27 per tonne.

Correcting soil pH

Fox argues that the application of lime has an influence on the availability of stored nutrients in the soil. The optimum pH of soils for grassland is pH 6.3. The target is to have soil at the optimum pH in order to optimise soil fertility. If the lime requirement is greater than 7.5 t/ha, it should be split into 2 dressings in year 1 and year 2.

Some farmers may choose to apply granulated lime compared to ground lime, and while more expensive, it has a quicker response and should be treated as a fertiliser, being applied each year. When the soils are acidic and there is a lime requirement, chemical and organic fertiliser won’t perform to the maximum. And if soils require lime, the availability of the essential nutrients are reduced as they are bound to the clay particles in the acidic soil – therefore it is important to optimise the soil pH as this will increase the availability of soil nitrogen, phosphorus and potassium.

Applying lime

Maintaining optimum soil fertility increases the efficiency of applied nitrogen from 35% on low fertility fields to 63% on field with an optimum pH, phosphorus and potassium. Once fields have been grazed-off and grass covers are low, Fox believes it is an ideal time to apply lime.

“Identify blocks of land that require lime; for example, this could require ordering a load of lime (20 t) after each grazing rotation to correct soil pH. Aim to avoid high grass covers >600 kg DM/ha.”

Spreading cattle slurry on fields that have received lime recently or freshly limed land where the lime has not had a chance to be washed into the soil can result in a loss of 50% of the available slurry nitrogen. To minimise these nitrogen losses from slurry, apply cattle slurry first and then apply the lime 7-10 days later.

Urea

For urea, a similar situation to cattle slurry where increased nitrogen loss (ammonia-nitrogen volatilisation) may occur, where straight urea fertiliser is applied on recently limed land. Fox therefore again stresses the need too apply the lime 7-10 days later to reduce the risk of nitrogen 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.

Silage ground

Fox makes the following points:

• 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).
• In the current year, it is very important for farms to keep cost to a minimum and only spread fertiliser on silage ground and grazed ground if farmers are going to utilise it.
• Ensure that slurry goes on silage ground first as it is very valuable in the current situation.

Fellow Teagasc drystock adviser, Shane Devaney, says farmers should apply lime to grazing ground as soon as the weather permits to ensure benefits are realised later in the spring and summer.