Acidic Soil Can Be Neutralized by Adding Lime: 7 Ways

Acidic soil can be neutralized by adding lime, and the usual choice is ground agricultural limestone (calcium carbonate). The carbonate reacts with the hydrogen ions that make soil acid and raises the pH, as University of Maryland Extension explains. For most field crops the target is a pH of about 6.0 to 7.0, according to Penn State Extension.

Quicklime and hydrated (slaked) lime also neutralize acid soil. Clemson says hydrated lime acts more rapidly than limestone. Gypsum and Epsom salts do not, even though they contain calcium or magnesium. This page compares seven liming materials by strength, shows the lime rate a soil test gives you, and has a calculator for tons and cost per field.

Which substance neutralizes acidic soil?

Farmers add liming materials: carbonates, oxides or hydroxides of calcium and magnesium. Penn State lists ground calcitic and dolomitic limestone, burnt lime (calcium oxide), hydrated lime (calcium hydroxide), marl and shells, slags and some industrial by-products. About 99 percent of the aglime used in Pennsylvania is ground limestone (Penn State Extension, last updated 2014).

Some common household and lab chemicals are not field options. Penn State states that calcium sulfate (gypsum) and magnesium sulfate (Epsom salts) are not liming materials, because they cannot neutralize soil acidity. Strong acids and other lab reagents do not belong on a field at all. If a quiz asks which substance neutralizes acidic soil, the answer is lime.

Why lime works on acidic soil

Soil pH is a logarithmic scale. A one-unit change is a ten-fold change in acidity, so a small pH gap can mean a large lime need (Penn State Extension). In the soil, the carbonate part of lime binds hydrogen ions. The calcium itself does not do the neutralizing work (University of Maryland Extension).

What goes wrong in acid soil:

• Below pH 5.5, aluminum and manganese dissolve and can reach levels that damage roots, and calcium and magnesium uptake falls (Penn State Extension).
• Phosphorus binds to aluminum and iron in acid soil. Penn State suggests keeping pH between 5.5 and 6.8 to limit phosphorus problems.
• Nitrogen-fixing Rhizobia bacteria in legume roots become less active below pH 6.0 (Penn State Extension).
• Liming fine-textured soils can improve structure, with less surface crusting and better emergence of small-seeded crops (Penn State Extension).

The yield cost can be large. The Arkansas Wheat Production Handbook says wheat growth and yield may be reduced by 20 to 50 percent when soil pH is below 5.6, and the handbook says 24 percent of the state’s wheat acres had a pH below 5.4 in an earlier survey it cites (no year given) (University of Arkansas Division of Agriculture, updated 2014). In North Carolina, about 58 percent of mineral soil samples submitted for cotton in fiscal year 2020 needed lime (NC State Extension, 2026 Cotton Information).

Acidity builds up over time. Rain leaches calcium, magnesium and potassium out of the root zone, crops remove them at harvest, and ammonium-based nitrogen produces acid. That is why a field that tested fine ten years ago can need lime now. Retest every few years.

▶ Why soil organic matter matters for farming. · 7:33

Test first: how much lime does your field need?

Liming without a soil test is guessing. A test gives two numbers: pH, and the reserve (exchangeable) acidity that sets the lime amount. Penn State says the lime amount depends on the reserve acidity and the crop’s target pH, not on pH alone (Penn State Extension).

Sample at the right depth. Purdue Extension advises separate 0 to 4 inch samples for pH and liming in conservation-tillage fields, and 0 to 8 inches under conventional tillage (Purdue Extension, AY-368-W). Iowa State notes that lime rates for no-till, pasture and hay (2 to 3 inch sampling) are set for a shallower layer of soil. Samples taken to 6 inches can be used, but the lime rate should be cut to about half (Iowa State University Extension). Tell the lab the depth you sampled.

Targets differ by crop and state. For corn and soybean, Iowa State sets pH 6.5 where the subsoil is acid and 6.0 where it is naturally high in lime. For alfalfa it recommends 6.9. Penn State says legumes and barley respond better at pH 6.5 to 7.0, while oats tolerate 5.5. Use your state laboratory’s target.

7 ways to neutralize acidic soil with lime

These are the seven liming materials and forms in use, with what the extension sources say about each. CCE is the calcium carbonate equivalent: how much acid the material neutralizes compared with pure calcium carbonate (100).

1. Ground agricultural limestone (calcitic)

The standard choice. Pure calcitic limestone has a CCE of 100 by definition, and real products vary with purity. Fineness matters too: the finer the particles, the faster the lime works (Clemson Extension, reviewed May 2026). University of Florida notes that calcitic lime raises pH faster than dolomitic lime (UF/IFAS Extension).

Best for: acid soils where magnesium is not short. Limit: it reacts slowly, so apply it months ahead of acid-sensitive crops.

2. Dolomitic limestone

Dolomitic limestone has a CCE of about 109 (Penn State Extension) and supplies magnesium as well as calcium. Oregon State says magnesium shortage on acid soil can be corrected with dolomitic lime (Oregon State Extension, EC 1478). University of Florida advises choosing between dolomitic and calcitic mainly on price, and warns that dolomite used only as a magnesium source can cause other nutrient problems where pH is above 6.3.

Best for: acid soils that test low in magnesium. Limit: skip it if soil magnesium is already high.

3. Quicklime (calcium oxide)

Burnt lime has a CCE of 179, the highest of the common materials, so less product neutralizes the same acidity (Penn State Extension). It is reactive. Wear gloves, eye and breathing protection, follow the supplier’s safety sheet, and mix it into the soil rather than leaving it in a layer.

Best for: cases where a supplier recommends it and the equipment and training are in place. Limit: handling risk.

4. Hydrated (slaked) lime

Hydrated lime, calcium hydroxide, has a CCE of 136 (Penn State Extension). Clemson Extension says to use it with caution because it neutralizes acidity more rapidly than regular limestone (Clemson Extension). Too much, too fast, can overshoot the target pH.

Best for: small areas, gardens and greenhouse beds. Limit: easy to overapply; dusty.

5. Pelletized and granular lime

Granular and pelletized lime are ground limestone made into pellets. Clemson (garden-scale guidance) notes they are less likely to clog fertilizer spreaders and are easier to apply on turf and lawns (Clemson Extension). Compare cost per unit of neutralizing power (CCE), not per bag or per ton of product.

Best for: small farms, lawns and spreaders built for fertilizer. Limit: price per unit of neutralizing power may be higher, so compare quotes.

6. By-products: water-treatment lime, slags, shells and ash

Marl and shells have a CCE of 70 to 90, and slags 60 to 90, while other industrial by-products vary (Penn State Extension). University of Florida says lime from municipal water treatment plants can work well, but it arrives as a wet paste, reacts quickly because it is so fine, and the suggested rate is about 80 percent of the limestone rate. By-products fall outside the lime-quality law in Florida, so the buyer takes on more responsibility (UF/IFAS Extension). Ask for a lab analysis of neutralizing value and contaminants first.

Best for: farms near a reliable, tested source. Limit: variable quality and spreading problems.

7. Fluid (suspension) lime

Fluid lime is finely ground lime mixed into water and applied as a liquid with special equipment. Ask the supplier for the same label figures you would want on dry lime: the CCE and fineness, plus the water content, so you can compare the cost per unit of neutralizing power. Test the field again after the next crop.

Best for: contractors that already run the equipment. Limit: needs special application equipment.

Compare the liming materials

The table shows the neutralizing value of each material from the Penn State tables. A higher CCE means you need less product for the same job. It does not show price or speed. Compare quotes in dollars per ton of CCE, not per ton of product.

Penn State’s example shows how labels work. A product with 35 percent calcium and 2 percent magnesium converts to a CCE of about 96 percent (35 x 2.50 plus 2 x 4.17). Lime recommendations are usually given in pounds of CCE per acre for a seven-inch layer of soil, so the actual product amount changes with the CCE, moisture and incorporation depth (Penn State Extension).

Chart

Neutralizing value of liming materials

Calcium carbonate equivalent (CCE), pure calcitic limestone = 100; midpoints for ranges

How much lime to apply, and when

The soil test report converts your pH and buffer reading into pounds of pure calcium carbonate per acre. Iowa State’s table shows how that figure rises as the buffer pH falls. Laboratories use different buffer scales and methods, and the Iowa values apply to its SMP and Sikora methods, so use your own lab’s table for your rate. The chart below plots the amounts for a 6-inch soil layer and a target pH of 6.5.

Chart

Lime rate rises as buffer pH falls

lb of calcium carbonate per acre to reach pH 6.5, 6-inch soil layer (SMP/Sikora buffer methods, Iowa)

Large requirements need care, and your lab or state guidance may set a maximum per pass. Penn State’s own rule of thumb for surface-acid no-till fields is 2,000 pounds of CCE per acre when the surface pH is under 6.2 and the standard test shows no lime need. Penn State suggests splitting a large requirement into two applications about six months apart, or working lime in by tillage, and smaller, more frequent applications for no-till (Penn State Extension).

Timing: Clemson, whose factsheet is garden-scale guidance, says to apply limestone two to three months before planting (Clemson Extension). NC State says at least three months for cotton (NC State Extension). Penn State notes even finely ground materials need several months to react. Lime also needs moisture, and mixing it into the soil improves contact.

Calculate the tons and cost for your field

Enter the lime requirement from your soil test report, the CCE and moisture from the supplier’s label, and a delivered price. The result is the product you need, total tons and the cost. All figures are examples. Replace them with your own.

Try the numbers for your own farm below.

Fertilizer keeps acidifying your soil

Ammonium-forming nitrogen fertilizers add acid every year. Penn State gives the pounds of calcium carbonate needed to offset one pound of nitrogen (these are Penn State figures; other services may quote different values): about 3 for urea, ammonium nitrate, UAN and anhydrous ammonia, 5.3 for DAP, and 7 for ammonium sulfate, MAP and APP (Penn State Extension). Clemson adds that ammonium or urea fertilizers speed up acidification (Clemson Extension).

Chart

Lime needed to offset 1 lb of nitrogen

Pounds of calcium carbonate per pound of N applied, by fertilizer

A field that gets 150 pounds of nitrogen per acre as urea needs about 450 pounds of calcium carbonate per acre to offset the acid, using the Penn State figure of 3 to 1. This is a rough guide, since leaching and crop removal add to it. Soil tests remain the guide.

Common liming mistakes

• Liming without a test, or sampling at the wrong depth. See the sampling notes above (Purdue Extension).
• Overliming. University of Florida says manganese and other micronutrient shortages can appear when pH goes above about 6.3 on its low-manganese soils, and that time is the best cure for an over-limed soil (UF/IFAS Extension). Oregon State notes micronutrient shortages rarely occur when pH is below 6.5 (Oregon State Extension).
• Buying by ton instead of by CCE and fineness. A cheaper product with a low CCE can cost more per unit of acid neutralized.
• Leaving reactive lime on the surface where roots need to feel the change, or spreading it on dry ground and expecting a fast result. Moisture is essential for the reaction (Clemson Extension).
• Treating gypsum as lime. It adds calcium or sulfur but does not raise pH.

Always follow the product label, your lab’s recommendation and local rules on spreading near water. For crop-specific rates or legal limits, ask your county extension office or a certified crop adviser.

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What about alkaline soil?

Searchers also ask how basic soil can be neutralized. Lime does the opposite: it raises pH. To lower the pH of alkaline soil, extension services point to elemental sulfur. Oregon State says elemental sulfur gives the most rapid reduction in soil pH, because soil bacteria oxidize it to sulfuric acid, and it must be mixed into the soil (Oregon State Extension, EC 1560). University of Florida cautions that sulfate forms of sulfur will not lower pH, and that where high pH comes from natural carbonates, lowering it across a whole field is impractical. Banding sulfur with micronutrients is suggested instead (UF/IFAS Extension).

Map lime zones with satellite data

Acidity often varies within a field, from knolls to low spots and across soil types. Zone sampling with GPS, as described by Purdue Extension, lets you map pH and apply different rates in each zone. Satellite vegetation maps cannot measure soil pH. They can show where crop growth is weak, so you know where to take extra soil samples. Farmonaut shows field vegetation maps through the season, and you can compare a patchy area with your soil test map.

Use the satellite map to choose sampling spots, then let the laboratory test decide the lime rate.

▶ How satellite NDVI maps show crop stress across a large farm. · 4:09

FAQ

What is added to acidic soil to neutralize it?

Lime. Ground limestone is the standard product. Quicklime, hydrated lime, dolomitic limestone and some by-products also work (Penn State Extension).

Why do farmers add lime to acidic soil?

Lime raises pH, which lowers aluminum and manganese toxicity, makes phosphorus, calcium and magnesium easier for roots to take up, and supports soil microbes and legume nitrogen fixation. Sources: Penn State Extension and Clemson Extension.

How long does lime take to work?

It depends on fineness, moisture, soil and how well it was mixed. Clemson recommends two to three months before planting; NC State at least three months for cotton. Hydrated lime acts faster than limestone.

How do I know how much lime to use?

Take a soil test with a lime-requirement (buffer pH) reading, tell the lab your crop and sampling depth, then adjust the recommended amount for the CCE of the product you buy. The calculator on this page does the adjustment.

Is slaked lime or quicklime better than limestone?

They neutralize more acid per ton, with CCEs of 136 and 179 against 100 for calcitic limestone, but they react fast and are harder to handle. Ground limestone is the standard choice and is easier to handle. Which is cheaper depends on local quotes, so compare the cost per unit of CCE.

Can I lower soil pH instead?

Yes, for alkaline soil. Elemental sulfur is the usual material. Lime will not help.

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