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Soil pH and Liming Facts
Successful crop production depends on a high level of soil fertility and on adequate soil pH. Prince Edward Island soils are naturally acidic (low pH) and require liming to improve crop production. the following points provide a reference to managing low pH soils:
- Soil pH is reported as measured in a water (H2O) solution. These measurements indicate how acid or alkaline the soil is. This measurement can be used to determine whether a soil needs liming or acidification.
- Soil pH values vary during the growing season by 0.25 units. The variation is usually greater on soils with a pH above 6.5 than on more acid soils.
- The buffering capacity of a soil is it's capacity to resist a change in pH.
- High buffering capacity soils need more lime to raise their pH levels by a given amount.
- Generally soils with high clay/organic matter levels have higher buffering capacities.
- The lime requirement of a soil is the amount of good quality limestone that should be added and worked in the top 20 cm (8-10 inches) to reach the target pH.
- The Soil and Feed Testing Laboratory provides lime requirement(s) on the soil test report when the crop to be grown or growing is specified.
- Hydrated lime or calcium hydroxide (Ca(OH)2) can be substituted for limestone but the liming recommmendations should be reduced by 25%.
- One of the principal reasons why hydrated lime neutralizes soil acidity more rapidly than limestone is because it is more finely pulverized.
- All liming materials have to be incorporated thoroughly into the plow layer to effect a rapid neutralization of the soil acidity.
- If the limestone cannot be incorporated into the plow layer the recommended rate may have to be reduced.
- If the liming recommendation exceeds approximately 7 tonnes per hectare (about 3 tons per acre) then 2 or more applications should be made.
- Dolomitic limestone contains magnesium (the content varies) and may be used to increase the levels of plant available magnesium on acid soils.
- Finer limestone particles have greater surface areas exposed to chemical reaction and will neutralize soil acidity faster than coarse limestone particles.
- Calcium is an important plant nutrient. Levels are adequate for plant growth by liming the soil to it's desired pH.
- Liming to raise the soil pH will increase the levels of available calcium in soils and generally also increase the concentration of calcium in crops.
- Liming may improve the soil structure of fine textured clay soils.
- Increasing the soil pH with liming will promote the decomposition (mineralization) of soil organic matter. Consequently, the liberation of plant nutrients in the organic matter may increase yields.
