Part 1, Section 2: Soil Fertility Management
Soil Fertility Management
SOIL ACIDITY AND LIMING
Fineness
A liming material must be finely ground to be effective. This is important because (1) limestone’s solubility increases as it is ground finer, and (2) limestone affects only a very small volume of soil around each particle. Therefore, more finely ground limestone has more particles and, if there is adequate mixing, neutralizes more of the soil with which it comes into close contact. The effect of limestone fineness on changing soil pH is illustrated in Figure 1.2-1.
In each case in Figure 1.2-1, sufficient aglime was applied to neutralize the soil acidity to raise the pH to 7.0. Note that material larger than 20 mesh was of little value for increasing soil pH and that only 100-mesh material came close to achieving that goal in a short time. Therefore, it would seem desirable to use only limestone that is 100 mesh or smaller. However, this decision must be balanced against the high cost of grinding limestone to finer than 100 mesh. A compromise must be reached so that the material is fine enough to be effective agronomically but still economically sound.
Pennsylvania aglime regulations classify agricultural liming materials into the following three groups based on fineness:
| 1. Fine-sized |
|---|
| 95% through a 20-mesh screen |
| 60% through a 60-mesh screen |
| 50% through a 100-mesh screen |
| 2. Medium-sized |
| 90% through a 20-mesh screen |
| 50% through a 60-mesh screen |
| 30% through a 100-mesh screen |
| 3. Coarse-sized |
| All liming materials that fail to meet one of the above minimums for fineness. |
A material meeting the standard for a “fine-sized” liming material is considered adequate for meeting soil test recommendations in most situations. It is assumed that fine-sized materials will react rapidly enough to effect a change in soil pH in the year of application and typically will remain effective for about three years. The medium- and coarse-sized materials are slower to react; thus they are less effective in changing soil pH during the year of application and take longer to react completely.
The actual fineness must be printed on the label. The calculations and table for adjusting your recommendations for the CCE of your liming material assume that the material meets the minimum fineness standards for fine-sized limestone. When selecting a liming material, there generally is little advantage in exceeding the minimum standards for fine-sized material. In emergency situations where a very rapid change in soil pH is required, paying extra for a finer material may be warranted; however, planning ahead by using a less expensive material and giving it time to react normally, generally will give better and more economical results.