Green light to apply lime as conditions suit

Every year, the question is put to Teagasc advisers by farmers: “When is the best time to apply lime?”

In answer, now is the best time while weather and ground conditions allow. Spreading lime in the autumn will encourage growth in the coming spring by releasing organic nitrogen and phosphorous from the soil, encouraging earthworm and microbial activity, increased uptake and utilisation of chemical NPK fertiliser by grass plants and tillage crops. Also, spreading lime in the autumn reduces the risk of lime being taken up in silage crops next year. Excess lime in mown grass will inhibit silage preservation, resulting in poor quality silage.

Importance of Lime

Lime is the foundation of all soil fertility, grass growth and livestock production. Lime, along with phosphorous (P) and potassium (K) are all essential grassland nutrients whose use has declined in recent years. Ask most farmers when they last spread lime, and will they remember?

Lime can have a huge effect on animal thrive, resulting in extra liveweight gain and higher stocking rates. Lime supplies calcium and, in some cases, magnesium which is important for healthy bone development in livestock, for the production of milk and as a help towards reducing incidence of grass tetany.

Effects of Liming

Lime improves sward quality. It is necessary to correct soil acidity and facilitate healthy plant growth. Soil acidity is measured on the pH scale of 0 to 14. The optimum pH for good grassland is 6.3 to 6.5. Ryegrasses and clover perform best at this pH or higher, but are replaced by lower productive grasses, such as bent grass, when the pH drops below 6.0. Therefore, keeping grassland close to pH 6.3 is essential to maintain ryegrasses and clover.

Liming promotes soil micro-organisms and encourages earthworm activity that breaks down plant and animal residues to release plant nutrients, especially nitrogen. It is estimated that by liming an acid soil (pH 5.5), up to 75kg to 80kg of free nitrogen (48-64 units) is released from the soil per hectare annually.

Liming improves the availability of phosphorous to plants and aids its release from organic matter. At a time of high fertiliser prices, keeping soils at the recommended pH is a good investment.

With lime, the correct pH allows optimum use of other nutrients such as potassium (K) or potash. Lime is the cement in the mix of NPK that makes them available to promote plant growth.

Lime Losses

Lime is lost from the soil mainly in drainage water. This loss is from 250 to 265kg per hectare/year, depending on the rainfall, soil type and the amount of lime in the soil at the start.

Crops and livestock remove lime. An average crop of silage or hay removes 60 to 80kg per hectare per year of limestone. A good bullock removes nearly 25kg/head/year. High fertiliser N usage will increase soil acidity, for example, each 1 kilo of N applied will require approximately 2 kilos of lime.

Low lime levels will only improve with regular applications of lime. Completing a soil test is the first step to correct any lime deficiency. A standard soil test will give the soil fertility status for pH lime requirement as well as phosphorus (P) and potassium or potash (K).Follow any soil recommendations given by a Teagasc adviser or agricultural consultant carefully.


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