How to compare limes and other amendments
Before you buy a lime, it pays to know what job it does and how much it really delivers. This guide helps you compare products; it does not tell you how much to apply.
Two different jobs
Correcting soil acidity and supplying nutrients are two different jobs. A product can do one, the other, or both.
Agricultural lime (calcium carbonate) and dolomitic lime neutralise acidity and aluminium and also supply calcium; dolomite supplies magnesium as well.
Agricultural gypsum supplies calcium and sulphur but does not raise the pH. That is why two products with “calcium” on the bag can do very different jobs in your soil.
What PRNT means
PRNT (relative total neutralising power) tells you how strongly a product corrects acidity compared with pure, finely ground calcium carbonate.
It combines two things: the product's chemical purity — its neutralising value — and how finely it is ground. A coarse lime reacts more slowly, even when it is pure.
A PRNT of 100% means the product acts like pure calcium carbonate. At a PRNT of 50% you need twice as much product for the same effect.
The comparison
Each row neutralises the same as 100 kg of pure calcium carbonate (CaCO₃):
| Product PRNT | Product needed | Equals |
|---|---|---|
| 50% | 200 kg | 100 kg of pure CaCO₃ |
| 75% | 133.3 kg | 100 kg of pure CaCO₃ |
| 100% | 100 kg | 100 kg of pure CaCO₃ |
The rule: kg of product = 100 × 100 ÷ PRNT.
The 100 kg is a unit for comparing products, not a dose.
Compare with your recommendation
Were you recommended one product and want to use another? Enter the amount and see how much of the other you need for the same effect, and what changes in calcium, magnesium and sulphur. The example shows 1,000 kg/ha of dolomitic lime: replace it with your recommendation.
Corrects the same acidity
1,083 kg/ha
of Agricultural lime
PRNT 65 % → 60 % SoilApp · to calibrate
| kg/ha | Dolomitic lime | Agricultural lime | Difference |
|---|---|---|---|
| CaO | 310 | 574 | +264 |
| MgO | 200 | 0 | −200 |
You stop applying 200 kg/ha of MgO.
CaO, MgO and S contents: typical SoilApp values. Your bag may differ: check the label.
Calculated for 1,000 kg/ha of Dolomitic lime.
The most common products
Typical values; your bag may differ, so check the label. In the calculator above you can enter the PRNT printed on your bag.
| Product | Corrects acidity? | PRNT | CaO % | MgO % | Other | Use it if… |
|---|---|---|---|---|---|---|
| Limes: correct acidity and supply nutrients | ||||||
| Agricultural limecalcium carbonate | Yes | 60 % SoilApp · to calibrateCenicafé measured 62–93% | 53 | 0 | — | your magnesium is fine and you want to correct acidity. |
| Dolomitic limecalcium magnesium carbonate | Yes | 65 % SoilApp · to calibrateCenicafé measured 64–89% | 31 | 20 | — | your magnesium is low. |
| Compound amendmentsblends with silicate, gypsum or rock phosphate | A little | Not verifiedCenicafé measured 46–52% | Varies: read the label | Varies: read the label | S, P and SiO₂ in varying amounts | you know its PRNT: ask for it before buying, as they often correct less than they seem to. |
| Hydrated limeslaked lime | Yes, fast | 122 % SoilApp · to calibrateCenicafé measured 93–115% | 70 | 0 | — | you are about to plant: it acts fast, but is not used on established crops. |
| Quicklimecalcium oxide | Yes, very fast | 160 % SoilApp · to calibrate | 90 | 0 | — | you are about to plant: it is caustic, handle it with protection and do not use it on established crops. |
| Supply nutrients, hardly correct acidity | ||||||
| Agricultural gypsumcalcium sulphate | No | — | 32 | 0 | S 18 | you need calcium and sulphur without raising the pH. |
| Magnesium sulphatekieserite | No | — | 0 | 25 | S 20 | you need magnesium without changing the pH, for example when using agricultural lime. |
| Rock phosphatephosphorite | Hardly | Cenicafé measured 10–16% | 35 | 0 | P₂O₅ 28 | you want slow-release phosphorus; it does not correct acidity. |
If you swap dolomite for agricultural lime in the amount that corrects the same acidity, you stop supplying magnesium. If your soil is low in magnesium, review with your advisor how to make up for it, for example with magnesium sulphate.
- CaO, MgO, S and P₂O₅: typical content according to SoilApp; your bag may vary.
- “SoilApp · to calibrate”: the default NutriPlan uses when the label is silent; not yet measured in the field.
- “Cenicafé”: PRNT measured on products sold to coffee growers (Avance Técnico 516, 2020).
- “Not verified”: there is no reliable source, so we show no number.
How to read the label
- The PRNT. If the label does not state it, ask the supplier in writing; do not assume it.
- The calcium and magnesium content, and whether it is stated as oxide (CaO, MgO) or as element (Ca, Mg). It is not the same number: 10% CaO is about 7% Ca.
- Fineness: how much of the product passes each mesh. The finer it is, the faster it reacts.
What this guide does not do
It does not give you a dose: how much lime your plot needs depends on your soil analysis, the crop and the depth you want to correct.
Nor does it give the PRNT of any brand: always use the value the manufacturer declares.
Ready to apply it on your farm?
See how a soil analysis becomes a plan per plot.