How much lime per hectare? A guide for acid soils

What sets the rate

Soil Quality's national fact sheet says the amount of lime depends on the soil pH profile (top and lower layers), lime quality, soil type, farming system and rainfall. The NSW version adds the topsoil's ECEC (how many nutrients the soil can hold). ECEC is higher in clays than sands, so clays need more lime for the same pH shift.

• Buffering. A well-buffered soil resists pH change: it turns acid more slowly but takes more lime to fix (Corangamite CMA Brown Book, Victoria).
• Organic matter. Queensland guidance says soils high in organic matter and clay need larger rates. The Brown Book says peaty soils need more lime than low organic matter soils.
• How far, and how deep, you need to move pH.
• The lime itself: its neutralising value and fineness (see below).

Field experiments cited in Victoria's Brown Book found it took up to 1.5 t/ha on sandy soils and up to 5 t/ha on clay loams to raise pH by one unit. Treat these as rough guides. Queensland guidance recommends asking the lab for a 'Lime Requirement' or 'Buffer pH' test, which gives a rate to lift the top 10 cm of a hectare to a target pH.

Choose a target pH

Most targets use pH measured in calcium chloride (pHCa). pH in water can read 0.6–1.2 units higher, so check which one your report shows. See reading a soil test.

• Soil Quality (national, WA-based): keep the topsoil above pHCa 5.5 and the subsurface above 4.8.
• Soil Quality's NSW sheet (revised by NSW DPI, 2013): topsoil above 5.2 and subsoil above 4.8.
• Queensland: a target of 5.5 is generally suggested for the lime requirement test.
• Victoria (Brown Book): consider lime once pHCa drops below 5.0 if you grow sensitive species.
• Tasmania: lime if surface pH (in water) is below 5.5.

Correction versus maintenance

• Recovery (correction): the topsoil is below target, so you apply enough to lift it back. Soil Quality's Tasmanian sheet suggests at least 2.5 t/ha for a good response, and no more than 7.5 t/ha in one go.
• Maintenance: topsoil and subsurface are both above target, so you apply enough to cancel the ongoing acidification from farming.

Victorian guidance says paddocks need re-liming about every 10 years, depending on how fast they re-acidify. Your nitrogen choice matters too: Queensland rates ammonium sulphate, MAP and DAP as highly acidifying and urea as medium. See urea vs ammonium sulphate.

In WA, surveyed growers said their most common rates would rise from 1–1.5 t/ha to 1.5–2 t/ha, but in many cases much more lime is needed to recover the profile. Across 69 WA lime trials, liming lifted grain yield by 0.2 t/ha (10%) on average.

Lime quality: neutralising value and fineness

• Neutralising value (NV) compares a product with pure calcium carbonate, which scores 100. The Brown Book says NV should ideally be over 95.
• Fineness. In Victoria, lime sellers must state the share of particles finer than 0.25 mm. Very fine lime has 98–100% fines, and that is the grade to buy.
• Finer lime reacts faster, which helps when you are recovering acid soil. Higher NV means less lime for the same pH change.

To convert a rate given for pure lime: tonnes needed = pure-lime rate × 100 ÷ NV. For example, 2 t/ha at NV 100 is 2.5 t/ha of an NV 80 lime.

Dolomite also carries magnesium. Soil Quality's Tasmanian sheet says good dolomite has an NV of 95–98% with 22% calcium and 12% magnesium, but warns that constant use may cause a nutrient imbalance.

Granulated ultrafine products are another option. Calciprill lists NV 95 and Magprill (granulated dolomite) NV 98 in their brochures; there is also Calciprill +B with boron. Their brochure rate guides (for example 300 kg/ha top-dressed for a 0.5 pH rise on sands) are well below the independent figures above. Treat those as manufacturer claims and ask for the trial data. Compare Calciprill and Magprill, or browse calcium products.

Subsurface acidity and depth

• Sample the surface and the subsurface (for example 10–20 and 20–30 cm), and repeat every 3–4 years. The Brown Book says field kits should not be used to set lime rates.
• Lime if the subsurface is below pHCa 4.8, even if the topsoil is fine. An acid band at 10–20 cm still blocks roots from better soil below.
• Keeping the topsoil above 5.5 lets enough alkalinity move down to treat subsurface acidity.
• Lime moves slowly, about 0.5–1 cm a year. Working it into the top 10 cm or deeper speeds it up; incorporated lime lifts 0–10 cm pH within 1–3 years (Tasmania).
• South Australia's 'catch-up' estimate aims to raise acidic 0–10 cm soil to pHCa 5.5 and acidic 10–20 cm layers to 5.0.

Always check with your agronomist before acting. If your soil also crusts or goes milky when wet, read gypsum vs lime.