FREQUENTLY ASKED QUESTIONS
The following are answers to some of the most commonly asked questions in relation to lime and managing soils that have been recently limed.
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Calcium limestone is the most common form of ground limestone available. Where dolomitic (Magnesium / Mg) limestone is used as a liming material, it is important that it is not used repeatedly without monitoring the soil Mg levels. The release of such Mg can be very slow, and frequent use of dolomitic limestone can cause soil Mg to rise to very high levels where it can impede the availability and uptake of other nutrients such as K.
The lime requirement is calculated in the laboratory based on a test that measures the soils buffering capacity. The buffering capacity is a measure of how much lime it takes to change the pH of the soil to the target pH.
Lime contains calcium and magnesium both of which are alkaline. The calcium and magnesium ions replace acidic hydrogen and aluminium ions through cation exchange. The full effects of lime may take two years to have an effect on soil pH.
If slurry is first applied, leave 1 week before spreading lime. If lime has been applied, avoid slurry application for three months.
Where there is either a history or risk of soils or herbage being high in Mo, it is recommended to reduce the lime application by 5t/ha. However this is a crude estimation and can be tailored for each situation depending on previous experience.
Problems with high Mo tend to be more common on wetter soils (or in wetter years) in swards with low ryegrass and/or high clover content and where annual rates of nitrogen fertiliser application is low.
To reduce the potential for Mn deficiencies, ensure lime is well incorporated during soil cultivations and seedbeds are well consolidated after sowing.
For silage it is better to apply lime before mid March for first cut or within one week after cutting on land which is being closed for a second cut as the presence of lime on the grass can increase the pH in the silage pit which affects silage preservation. Applying lime to heavy covers of grass intended for silage can reduce silage quality if the lime is not washed off the grass by rain.
The lime requirement is calculated in the laboratory based on a test that measures the buffering capacity of the soil. Buffering capacity is a measure of how much lime it takes to change the soil pH. Therefore soils that are returned with the same soil pH may be shown to have different lime requirements This is because the soils have different buffering capacities and require more or less lime to achieve the same increase in pH.
Soils that are heavier textured or have higher organic matter contents tend to have higher buffering capacities and higher lime requirements as a result. However while these soils may require more lime following the soil test, the higher buffering capacity should result in the soil retaining lime better in the future once it has been applied.
Specific requirements contained in SI 248/78 are as follows:
Product must have a Total Neutralising Value (TNV) of not less than 90%
All the product must pass through a 3.35 mm sieve.
Not less than 35% of the product must pass through a 0.15 mm sieve
The moisture content of the product must be less than 3.0%