Soil Liming

Why pH Alone Is Not Enough to Select a Liming Material and Its Application Rate

Knowing soil pH alone is not enough to select a liming material. You need to assess the need to neutralise acidity, soil properties, magnesium availability, crop requirements, and the quality of the liming material. Two fields with the same pH may require different application rates.

What Is Soil Liming?

Liming is the application of materials capable of neutralising excess soil acidity. It helps create more favourable conditions for root development and crop nutrition when acidic soil conditions limit crop growth.

Under excessively acidic conditions, the risk of aluminium and manganese toxicity increases, while phosphorus availability may decrease. However, the target pH is determined for the specific soil and crop rotation: there is no need to bring every field to pH 7.

Why Does pH Not Determine the Liming Rate?

pH indicates the reaction of the soil environment, but not the entire reserve of acidity that needs to be neutralised. Additional indicators and methods suitable for the relevant soil type are used to determine the lime requirement.

A light sandy soil generally offers less resistance to pH changes than a clay soil with a higher organic matter content. Therefore, even with the same initial pH and target soil pH, the required application rates may differ.

Pay attention to how pH was measured: in water or in a salt extract, such as KCl. These results cannot be interpreted using the same scale without accounting for the method. Check with the laboratory which method the thresholds and recommendations refer to.

What Do Buffering Capacity, CEC, and Base Saturation Mean?

Buffering capacity is the soil’s ability to resist changes in pH. It is influenced by soil texture, organic matter, and the properties of clay minerals.

Cation exchange capacity, or CEC, describes the soil’s ability to retain and exchange positively charged ions. Base saturation indicates the proportion of CEC occupied by calcium, magnesium, potassium, and sodium, as determined by the laboratory method.

These indicators help describe the soil, but they do not replace the determination of its lime requirement. CEC is not a direct measurement of buffering capacity. Calculations use indicators such as hydrolytic or exchangeable acidity, or a buffer test, depending on the laboratory method adopted.

When Should You Choose Limestone, and When Should You Choose Dolomite?

Limestone materials, including ground limestone based on CaCO₃, neutralise acidity and supply calcium. They can be considered when the need for liming has been confirmed and additional magnesium is not required.

Ground dolomite contains calcium and magnesium carbonates. Applying dolomite is appropriate when acidic soil also has low magnesium availability. If the pH already meets the crop’s requirements, magnesium deficiency alone is not a reason for liming: another source of magnesium nutrition should be selected.

Acidic soil conditions do not automatically indicate a deficiency of both elements. The material should therefore be selected based on the combined analytical results, rather than solely on its name or calcium content.

Which Characteristics of a Liming Material Affect the Result?

In addition to calcium and magnesium content, check the material’s neutralising value, fineness of grinding, moisture content, and suitability for uniform spreading. These characteristics determine how much product needs to be applied and how quickly it will react in the soil.

Equal masses of two products do not necessarily have the same neutralising effect. Compare the cost of achieving the required effect per hectare, including delivery and application, rather than just the price per tonne.

How to Determine the Liming Rate for a Field

• Identify the crops in the rotation and the target soil pH together with an agronomist.
• Collect representative samples. Assess areas with different soil properties separately.
• Obtain a laboratory assessment of acidity and lime requirement, specifying the method and soil sampling depth.
• Check magnesium and calcium availability and select the type of liming material.
• Convert the laboratory lime requirement into an application rate for the specific product, accounting for its neutralising value, moisture content, and other relevant quality indicators.
• Coordinate the application and incorporation method with the tillage system. Allow sufficient time for the reaction before scheduling a follow-up soil test.

Do not use a universal formula based solely on pH. The recommendation must clearly state whether the requirement is expressed as a CaCO₃ equivalent or as the actual mass of a specific liming material. This will help avoid errors during purchasing and application.

Frequently Asked Questions About Liming

Can the Application Rate Be Determined from pH Alone?

pH alone is not enough for a sound field recommendation. A methodologically consistent assessment of lime requirement, information about the soil and crop, and the material’s characteristics are needed. Regional tables are applicable only within the conditions for which they were developed.

Should All Acidic Soils Be Limed in the Same Way?

No. The crop, initial acidity, buffering capacity, tillage depth, and properties of the liming material all matter. The requirement may vary even within a single field.

Is Dolomite Always Better Than Ground Limestone?

No. Dolomite supplies additional magnesium, which can be an advantage when magnesium is deficient. Where magnesium availability is sufficient, the choice depends on the quality of the materials, their neutralising effect, and application costs.

Does Every Calcium-Containing Fertiliser Reduce Soil Acidity?

No. The presence of calcium does not imply an ability to neutralise acidity. For example, gypsum is not a substitute for a limestone material when the aim is to raise pH.

Can Too Much Lime Be Applied?

Yes. An excessive increase in pH can reduce the availability of certain nutrients. This is why the application rate needs to be calculated for the target conditions, and the result should be monitored through soil testing after application.

Start with Data About Your Field

To select a liming material, prepare your soil test results, information about your crop rotation, and details of your tillage system. If you do not have a current soil analysis, contact Makosh about the “Soil Audit” service. Before ordering, confirm the list of indicators needed specifically to calculate the lime requirement.

Makosh Soil Audit
https://makosh-group.com.ua/audyt-gruntu/