Getting the most out of lime applications
Correcting acid soil conditions through the application of lime can have a significant impact on crop yields, especially with alfalfa. Liming is one of the most essential, but often overlooked, management decisions a producer can make.
One important aspect of liming is the time required for pH change to occur. It can take some significant time for lime to react and raise soil pH. The exact amount of time is generally a function of lime particle size and soil moisture. Smaller particles have more surface area, and react faster in the soil. So when time is of the essence, using finely ground lime materials will result in a quicker pH increase.
Research has shown that the fine particles in ag lime, generally those that are smaller than 60 mesh, will react within 30 days. As particle size increases, the rate of reaction slows, since the relative surface area decreases as particle size increases. Particles between 30 and 60 mesh size may take as long as 1 to 2 years to react, while those between 8 and 30 mesh may take as long as 5 years or more. This is especially important when liming for new alfalfa seedings. Since seeding alfalfa is expensive and a stand is expected to last for several years, getting lime applied early enough to get the acidity problem corrected before seeding is critical.
Unfortunately lime is not always available close to where it may be needed. In many cases trucking and spreading costs may be more than the cost of the lime itself. Lime quality can also vary widely and no one wants to apply more than is necessary. So to make the best decisions on how much and what kind of lime to apply, it is useful to know how lime recommendations are made.
Crop Sensitivity To pH And Regional Differences In Target pH
A routine soil test will reveal the pH level of the soil, and this will determine whether lime is needed on the field. Crops differ in their sensitivity to low pH. In most cases, our crops are tolerant to pH levels in the higher ranges, as long as they don’t exceed pH 7.0. So it is generally best to lime to satisfy the needs of the most acid-sensitive crop commonly grown on that field.
Alfalfa is the crop most sensitive to acidity, and requiring the highest pH. Soybeans and red clover are intermediate, doing best at pH 6.0 to 6.4 in most areas; and wheat and corn are the most acid-tolerant crops.
Lime rates are given in pounds of effective calcium carbonate, ECC, per acre. Soils with more clay and organic matter (higher cation exchange capacity) will have more reserve acidity at a given pH, and will require more ECC to reach a target soil pH, than will a sandy soil. This is why two soils may have the same soil pH but have quite different buffer pHs, and different lime requirements.
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