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HOME / LABORATORY SERVICES / SOIL, FEED AND WATER CHEMISTRY TESTING LABORATORY / SPECIAL PRODUCTS TESTING /

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:

1. 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.
2. 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.
3. The buffering capacity of a soil is it's capacity to resist a change in pH.
4. High buffering capacity soils need more lime to raise their pH levels by a given amount.
5. Generally soils with high clay/organic matter levels have higher buffering capacities.
6. 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.
7. 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.
8. Hydrated lime or calcium hydroxide (Ca(OH)²) can be substituted for limestone but the liming recommmendations should be reduced by 25%.
9. One of the principal reasons why hydrated lime neutralizes soil acidity more rapidly than limestone is because it is more finely pulverized.
10. All liming materials have to be incorporated thoroughly into the plow layer to effect a rapid neutralization of the soil acidity.
11. If the limestone cannot be incorporated into the plow layer the recommended rate may have to be reduced.
12. If the liming recommendation exceeds approximately 7 tonnes per hectare (about 3 tons per acre) then 2 or more applications should be made.
13. Dolomitic limestone contains magnesium (the content varies) and may be used to increase the levels of plant available magnesium on acid soils.
14. Finer limestone particles have greater surface areas exposed to chemical reaction and will neutralize soil acidity faster than coarse limestone particles.
15. Calcium is an important plant nutrient. Levels are adequate for plant growth by liming the soil to it's desired pH.
16. 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.
17. Liming may improve the soil structure of fine textured clay soils.
18. 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.