Question 1

How much lime do I need per acre to raise pH?

Accepted Answer

The amount of lime needed per acre to raise soil pH depends heavily on your soil type. Sandy soils need the least — approximately 1–4 t/acre to raise pH by 1.0 unit. Clay soils need significantly more — 5–9 t/acre for the same pH increase. Peaty soils can require 8–14 t/acre. This is because clay and organic matter act as pH buffers, resisting change. This calculator uses the AHDB RB209 lime requirement tables which are the standard UK reference for lime recommendations.

Question 2

What is soil pH and what should it be?

Accepted Answer

Soil pH is a measure of acidity or alkalinity on a scale of 0–14. Most UK agricultural soils fall between pH 4.5 and 8.0. The optimal pH for most arable crops is 6.5 — below this, phosphorus becomes less available to plants and aluminium toxicity can occur. Grassland targets a slightly lower pH of 6.0–6.2. Sugar beet and most brassicas prefer pH 7.0. Potatoes are more tolerant of acidity and are typically grown at pH 5.8–6.0 to reduce scab disease pressure. Below pH 5.5, most cropping becomes uneconomic without liming.

Question 3

What is neutralising value (NV) in lime?

Accepted Answer

Neutralising value (NV) is the measure of a lime product's ability to neutralise soil acidity, expressed as a percentage relative to pure calcium oxide (CaO). Ground limestone has an NV of around 50%, meaning it takes twice as much ground limestone as burnt lime (NV ~90%) to achieve the same pH correction. The NV is always stated on the product delivery note and should be used to adjust the application rate accordingly. This calculator automatically adjusts the rate for your chosen lime product's NV.

Question 4

How often should I apply lime?

Accepted Answer

Soil pH should be tested every 3–4 years on arable land and every 4–5 years on permanent grassland. On most UK farms, lime is needed every 5–10 years depending on soil type, rainfall (acid rain leaches calcium), and cropping system. Heavy rainfall areas like Wales, Scotland and the West of England lose calcium faster and may need more frequent applications. Avoid applying more than 7.5 t/ha of ground limestone in a single application — split large requirements over two seasons to avoid over-liming.

Question 5

Can I apply lime and fertiliser at the same time?

Accepted Answer

No — lime and most nitrogen fertilisers (particularly ammonium-based products like AN or urea) should not be applied at the same time. Lime reacts with ammonium to release ammonia gas, causing significant nitrogen losses. Leave a minimum of 4 weeks between lime and nitrogen applications. Lime and phosphate fertilisers can be applied together, as lime does not significantly affect phosphate availability at normal application rates. On grassland, avoid applying lime within 2 weeks of applying slurry.

Question 6

Should I apply lime before or after ploughing?

Accepted Answer

On arable land, lime is best applied to the surface 2–6 months before ploughing so it can start working into the topsoil before being incorporated. Applying immediately before ploughing buries the lime before it can start reacting. On established grassland, lime is applied to the surface and relies on rainfall to work it into the upper soil horizon — this is slower but effective. Avoid applying lime to frosted or waterlogged ground.

Question 7

What is the difference between ground limestone and magnesian limestone?

Accepted Answer

Ground limestone is calcium carbonate (CaCO₃) with an NV of around 50%. It is the standard agricultural lime and the most widely used. Magnesian limestone (also called dolomitic limestone) contains both calcium carbonate and magnesium carbonate, and typically has an NV of 55%. It is useful on soils with confirmed magnesium deficiency — if your soil analysis shows a low Mg index (Index 0), magnesian limestone kills two birds with one stone. Do not apply magnesian lime routinely without a soil test showing Mg deficiency, as excess magnesium can cause soil structural problems.

Soil Type	pH +0.5	pH +1.0	pH +1.5	pH +2.0	pH +2.5	pH +3.0+
Sand / Light Sandy	2.5	4.5	6.5	8	9.5	11
Sandy Loam	3.5	6	8.5	11	13.5	16
Loam	4.5	7.5	11	14	17	20
Clay Loam	5.5	9.5	13.5	17.5	21	25
Clay / Heavy Clay	7	12	17	22	27	32
Peaty Mineral	9	15	21	27	33	39
Peat	12	20	28	36	44	52

Lime Application Rate Calculator

Soil pH

Soil type

Field & product

UK Lime Requirement Reference — Ground Limestone (t/ha)

Frequently Asked Questions — Lime Application