How is a lime requirement calculated?

Multiply the liming factor for your soil type and land use by the difference between your measured soil pH and the target pH, which is 0.2 above the optimum pH for your cropping system. The result is tonnes per hectare of ground limestone or chalk at neutralising value 50. This is the method given in AHDB RB209 Section 1, Table 1.2.

What is the optimum soil pH for arable land?

RB209 Table 1.1 gives an optimum of pH 6.5 for continuous arable cropping on mineral soils, 6.2 on organic soils and 5.8 on peaty soils. For continuous grass or grass-clover swards the optimum is 6.0 on mineral soils. Lime to a target 0.2 pH above the optimum.

Does the type of liming material change the rate?

Yes. RB209 expresses recommendations as tonnes of ground limestone or chalk at neutralising value (NV) 50 to 55, and states that the application rate is adjusted to take account of differences in NV. A material with a higher NV neutralises more acidity per tonne, so less is needed. Hydrated lime is about NV 70, burnt lime about NV 80 and sugar beet lime 22 to 29.

Why does clay need more lime than sand?

Clay and organic soils buffer pH more strongly, so more lime is needed to raise pH by the same amount. RB209 liming factors reflect this: 6 for sands and loamy sands under arable cropping, 7 for sandy loams and silt loams, 8 for clay loams and clays, 10 for organic soils and 16 for peaty soils.

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Lime Requirement Calculator

Enter the pH from your soil analysis and get tonnes of lime per hectare, using the liming factors and target pH values in the AHDB Nutrient Management Guide (RB209), Section 1.

England and Wales. RB209 methods are for soils in England and Wales. For Scottish soils see FAS Technical Note TN714.

Your field

Measured soil pH From your soil analysis, or a field test kit Soil type Clay and organic soils need more lime than sands Cropping system Sets the optimum pH from RB209 Table 1.1

Depth being corrected

Topsoil Subsoil (20–40 cm)

Topsoil = 20 cm cultivated, or 15 cm grassland

Liming material Rates are quoted at NV 50 and adjusted for your material

Area (optional)

ha acres

To get the total tonnage to order

How this works

RB209 gives the calculation directly: multiply the liming factor for your soil type and land use by the gap between your measured pH and the target pH, where the target is 0.2 above the optimum for your cropping system. The answer is tonnes per hectare of ground limestone or chalk at neutralising value 50.

Liming factors (RB209 Table 1.2)

Soil type	Arable	Grass
Sands and loamy sands	6	4
Sandy loams and silt loams	7	5
Clay loams and clays	8	6
Organic soils	10	7.5
Peaty soils	16	12
Subsoil (20–40 cm)	5	4

Optimum soil pH (RB209 Table 1.1)

Cropping system	Mineral	Peaty	Organic	Subsoil
Continuous arable cropping	6.5	5.8	6.2	6.3
Grass with an occasional barley crop	6.2	5.5	5.7	6.0
Grass with an occasional wheat or oat crop	6.0	5.3	5.5	5.8
Continuous grass or grass-clover swards	6.0	5.3	5.7	5.8

Lime to a target 0.2 pH above these values. Soil pH should not vary by more than ±0.5 of the optimum. Over-liming may trigger trace element deficiencies and faster lime losses, so this is not a case of “more is safer”.

Source

AHDB Nutrient Management Guide (RB209) — Section 1, Principles of nutrient management and fertiliser use, March 2026 edition: Table 1.1, Table 1.2 and the liming materials list.

Contains public sector information licensed under the Open Government Licence v3.0. This tool is a calculator, not advice — check the guide, and your own soil analysis, before ordering lime.