Lime Calculator (South Africa)

South Africa does not have one single lime-requirement method. The Western Cape mostly uses the Eksteen method, KwaZulu-Natal mostly uses the Cedara method, and the Free State has its own ARC Small Grain Institute method, among others. A 2017 Stellenbosch University study that ran all of these methods against the same real soils found they can disagree by two to ten times on the amount of lime recommended. That is not a typo, it is a genuine, published finding. This calculator uses the Cedara acid-saturation method, the one with the most complete, unambiguous published specification, and that same study found it tends to run somewhat conservative rather than over-recommend. If you have a figure from an accredited soil lab or your agronomist, it is the authoritative one for your soil, enter it directly in the first tab rather than relying on the estimate.

Acid saturation is the percentage of your soil's exchangeable cations that are aluminium and hydrogen, the acidic ones, rather than calcium, magnesium, potassium and sodium, the basic ones. It matters more than pH alone because crop damage from acid soils comes mainly from aluminium toxicity, and two soils at the same pH can have very different acid saturation and very different risk. Grain SA's general guidance is to manage acid saturation to 0 to 15 percent. Most international calculators instead use a buffer-pH test, SMP or Adams-Evans, that measures how strongly a soil resists a pH change. A South African soil lab report does not give you a buffer pH reading at all, so those calculators simply cannot be filled in correctly with a local soil test.

You need exchangeable acidity, aluminium plus hydrogen, in cmolc/kg, and your calcium, magnesium, potassium and sodium figures, which South African lab reports usually give in mg/kg. Tick the mg/kg option above and the calculator converts them for you using the standard equivalent weights. Exchangeable acidity itself is always reported in cmolc/kg, there is no mg/kg version of that figure.

It comes down to your soil's magnesium status. If your magnesium is low, below about 40 mg/kg, dolomitic lime is usually the better choice because it corrects the magnesium shortfall while it raises pH. If your magnesium is already adequate, calcitic lime is the better choice. A lot of South African fields have actually swung the other way after years of routine dolomitic lime use, carrying too much magnesium relative to calcium, which can harden and crust the soil surface over time. The calculator gives you a recommendation once you enter your soil magnesium.

No, and this is a common mix-up. Lime raises soil pH by neutralising acidity. Gypsum, calcium sulphate, does not change pH at all, it works by moving calcium down into the subsoil and displacing aluminium there, which is useful for subsoil acidity that ordinary surface-applied lime struggles to reach. Gypsum is not a substitute for lime on an acidic topsoil, and dolomitic lime is often applied together with gypsum specifically to restore the topsoil magnesium that the gypsum's calcium displaces downward. This calculator covers lime only, ask your agronomist about gypsum for subsoil acidity specifically.

South African law, Act 36 of 1947, sets minimum standards. Standard agricultural lime must have all its particles under 1 700 microns and at least half under 250 microns, while microfine or colloidal lime must have 95 percent under 250 microns and 80 percent under 106 microns. Both must have a minimum calcium carbonate equivalent, CCE, of 70 percent. Finer, higher-CCE lime reacts faster and neutralises more acidity per ton, which is exactly why the calculator asks for CCE% and works out cost per effective tonne rather than just cost per ton.

Lime is cheap per ton compared to most fertilisers, but it is heavy and bulky, so transport can easily cost as much as the lime itself, sometimes more over a long haul. A cheaper, coarser lime from a nearby quarry can beat a premium microfine product delivered from far away, or lose to it, depending entirely on the distance. The calculator lets you add a delivery cost per ton so the cost-per-effective-tonne comparison reflects the price actually landed on your farm, not just the ex-quarry price.

It depends on your lime requirement, the product you choose, and how far you are from a supplier, since cartage often costs as much as the lime itself. As a rough illustration at the July 2026 reference prices above, correcting 2 tons per hectare of standard agricultural lime costs roughly R700 to R900 a hectare before delivery, add your own cartage quote for the real landed figure. It is also worth knowing that bulk agricultural lime and small retail bags are priced very differently, a 25 or 50 kg bag from a hardware or garden store commonly works out to five to ten times the bulk agricultural price once you do the sums per ton, which makes sense for a small garden bed but not for a field. The calculator above works this out for your own area, product and delivery cost.

Lime needs to react with soil moisture and mix through the root zone, so the effect builds over weeks to months rather than happening immediately. Most agronomists recommend applying and working lime into the soil at least two months before planting so the reaction is substantially complete by the time the crop needs it. Finer, higher-CCE lime reacts faster than coarse standard lime.

The Cedara method used in this calculator is calibrated for lime worked into the top 20cm of soil, which is the standard depth for most row-crop liming. Lime that sits on the surface reacts very slowly, disking or ploughing it in is what gets the full benefit. Subsoil acidity below normal cultivation depth is a separate problem that surface-applied lime does not reach, that is where gypsum or deep incorporation comes in.

Yes. Over-liming wastes money for no extra benefit, and can push pH high enough to lock up micronutrients like manganese and zinc, causing new deficiencies. Repeated dolomitic lime use without checking magnesium levels is a common way South African fields end up with a skewed calcium-to-magnesium ratio, which can harden and crust the soil. This is exactly why the calculator works from your soil test figures rather than a generic rule of thumb, and why re-testing after liming matters.

Yes, ideally a season or two after application, once the lime has had time to react fully. Soil acidity is an ongoing process, nitrogen fertilisers in particular re-acidify soil over time, so liming is a maintenance task, not a once-off fix. A follow-up test tells you whether you hit your acid-saturation target and whether the next application, if any, should be smaller.

Lime prices vary a lot by region and distance from the source, since transport is often the biggest part of the landed cost. As a July 2026 reference point, standard agricultural calcitic lime is roughly R350 a ton and standard agricultural dolomitic lime roughly R360 a ton, ex-quarry, before delivery. Microfine or colloidal lime, finer and faster-reacting, costs more per ton but delivers more neutralising value, which is why comparing on cost per effective tonne rather than cost per ton matters. These reference figures are estimates, always get a delivered quote for your own area.