Ensure an optimum lime status for grazing swards to improve grass quality and intake.
Liming grassland is one of the best investments any dairy farmer can make, as it is often said that lime is the forgotten fertiliser.
Dr Jane Sayers, College of Agriculture, Food and Rural Enterprise (CAFRE) dairying adviser says that:
“Lime is the foundation of soil fertility, grass growth and subsequently milk production.” Lime, along with phosphorus (P) and potassium (K), is an essential grassland nutrient.
Jane outlines that:
“Lime is a soil conditioner, correcting soil acidity by neutralising the acids generated from nitrogen (N) fertiliser and slurry thus encouraging soil micro-organisms and earthworm activity to break down plant residues, animal manures and organic matter. This will encourage release of plant nutrients such as N, P, K and sulphur (S) and micro-nutrients for plant uptake and grass growth.”
Soil acidity is measured as soil pH which has significant influence on nutrient availability. Aim to maintain mineral soils in the pH range 6.3 – 7.0 and peat soils in the pH range 5.5 – 5.8 to maximise nutrient supply and optimise grass growth and production.
Benefits of liming are as follows:
Grassland soils can release up to 80kg N/ha (60 units N/acre) per year once restored to soil pH 6.3.
Maintaining the correct soil pH is critical for nutrient availability.
Increased persistence and productivity of rye grasses and clover.
Research shows where soil pH was increased from pH 5.5 to 6.3, the grass produced increased by at least an extra 1.0 tonne DM/ha annually.
Increased grass production from applying lime, to correct a deficiency, is worth at least £150/ha/year.
Every year, lime is lost from the soil through rainfall and drainage water. This loss can be from 250 to 265kg per hectare/year depending on the amount of rainfall, soil type and the amount of lime in the soil at the start.
Crops and livestock will also remove lime through cropping or grazing the sward. An average crop of silage removes 60 to 80kg per hectare per year of lime. A 400kgs dairy heifer removes nearly 25kg/head/year of lime from the soil through grazing.
Jane Sayers, CAFRE dairying adviser.
Jane advises that:
“High fertiliser N usage will increase soil acidity, for example, each 1 kilo of N applied will require approximately 2 kilos of lime. Consequently, aim to apply a maintenance level of lime to 20% of your dairy farm on an annual basis.”
It is advisable to sample soils in all fields on a regular basis (every 4 years) to determine lime requirements. Don’t exceed 7.5 t/ha (3.0 t/acre) lime in a single application. If you require application rates higher than 7.5 t/ha (3.0 t/acre), apply 50% now and reminder in 2 years’ time.
Follow the soil analysis recommendations carefully to avoid over or under liming. As a rule of thumb 2.5 t/ha (1.0 t/acre) application of lime will raise pH by 0.3 units on a medium textured mineral soil, so therefore if the pH is 5.5, an application of 5 t/ha (2 t/acre) will raise the pH to 6.1.
Jane continues that farmers should: “Target fields with the highest lime requirements first (low pH) and they should be limed as soon as possible. Lime can be applied at any time of the year; however, late summer and autumn are ideal as soils are usually drier and firm, there are increased spreading opportunities after cutting silage and grazing as there is less interference with slurry or N fertiliser applications.”
For grazing ground, apply lime to fields with very little grass cover (<1800 kg DM/ha), and avoid grazing until sufficient rainfall has occurred to wash the lime off the grass into the soil. Applying lime to grass intended for silage can reduce the silage quality if the lime is not washed into the soils by rain.
The type of N supplied in slurry and urea-based fertiliser is ammoniacal N and is prone to loss if applied to freshly limed soils. To avoid N loss, wait at least 3 months after liming before applying urea or slurry. Also allow 10 days after slurry or urea application before applying lime. Research indicates that no interval is required between liming and using protected urea.
Financial Benefits
Table 1 demonstrates as soil pH increases (5.0 to 6.0), nutrient utilisation increases. For example, at soil pH 6 applying one bag (50 kg) of straight N (27.0.0) over 89% nitrogen is utilised. In contrast at pH 5.0 only 53% nitrogen in the bag is utilised. In financial terms, this means for every 50 kg bag of 27% N/applied per acre costing £15/bag (£300/T), approximately 50% N or £7.50 is wasted. Over the grazing season if the equivalent of six bags of straight N is applied, £45 is lost (6 x £7.50), which would pay for spreading 2 t/lime per acre (5t/ha).
Table: Liming increases fertiliser performance
Lime Type
Calcium ground limestone will work over a period of months, with some 65% broken down and utilised within 6 months, while 35% can take up to two years to break down. It allows for steady pH adjustment. Magnesium (Mg) ground limestone is slower to react but has higher liming value.
Mg limestone may help reduce the incidence of grass tetany and Mg deficiency where soils are low in Mg. Granulated lime is fast acting and is flexible in that it can be applied with a fertiliser spreader however it is more expensive than ground limestone. It is very suitable if small amounts are required to maintain soil pH and can be applied every year. 125kg per ha (50kg per acre) of granulated limestone is considered equivalent to 370kg (150kg per acre) per ha of ground limestone.
Jane concludes: “It is important that dairy farmers do not neglect the lime status of their soils, carry out regular soil analysis and take every opportunity that arises throughout the year to apply lime to correct soil pH. Liming soils will bring major benefits in terms of soil nutrient availability and the more efficient use of applied nutrients encouraging more grass growth.”
Learn more about liming through the Soil Nutrient Health Scheme (SNHS) training or ask your local CAFRE adviser to help interpret the soil results.