Fourth tool in the Farming section, this one for working out how much agricultural lime you need.
Most lime calculators online are built for an American or British buffer pH test, SMP or Adams Evans, and a South African soil lab report simply does not give you that number. Here agronomists work in percentage acid saturation instead, the share of your soil’s exchangeable cations that are the acidic ones, aluminium and hydrogen, rather than the basic ones, calcium, magnesium, potassium and sodium. Grain SA’s general guidance is to manage that down to 0 to 15 percent. This tool uses the Cedara method, well documented and widely used in KwaZulu Natal, to turn your soil test figures into a lime requirement.
I want to be upfront about something I found while researching this. South African regions do not all agree on which method to use, the Western Cape mostly uses Eksteen, KwaZulu Natal mostly Cedara, the Free State its own ARC method, and a 2017 Stellenbosch University study that ran all of them against the same real soils found they can disagree by two to ten times on the amount of lime recommended. That is a genuinely large spread. So if you already have a figure from an accredited soil lab or your agronomist, it should win over this calculator’s estimate every time, there is a tab to enter it directly and skip the estimate entirely.
The part I think is actually useful is the product comparison. Two limes at the same price per ton rarely deliver the same neutralising value, since that depends on the calcium carbonate equivalent, CCE percent, and lime is heavy and bulky, so delivery often costs as much as the lime itself. A cheap coarse lime from a nearby quarry can beat a premium microfine product trucked in from far away, or lose to it, entirely depending on distance. The tool works out cost per effective tonne, adjusted for both CCE percent and delivery, so you can compare products honestly instead of just comparing the rand per ton on the price list. It also gives a dolomitic versus calcitic recommendation from your soil magnesium.
Reference lime prices came from a real, dated South African supplier price list rather than a guess, but prices vary a lot by region and distance from the quarry, so please check them against your own quote. If you use lime, I would value a sanity check on the numbers, and if gypsum versus lime is something you have questions about, there is an explainer in the FAQ on the page, gypsum does not raise pH the way lime does.