Part 1, Section 2: Soil Fertility Management
Soil Fertility Management
SOIL TESTING
Recommendations
Limestone recommendation
Limestone is applied to neutralize the acidity in the soil and thus raise the soil pH to the optimum range for crop growth. The limestone recommendation is based on the amount of exchangeable acidity measured in the soil and the optimum soil pH level for the crop. The recommended limestone application is a one-time application to cover the three years on the test. For most agronomic crops, the optimum pH is 6.5. For alfalfa and barley, the pH goal is 7.0. The pH requirements vary from crop to crop. However, because only one limestone recommendation is made for three years, the recommendation on the report will adjust the pH for the most sensitive crop to be grown during the three years. The actual pH goal used to make the limestone recommendation is indicated next to the recommendation on the report.
Lime requirement can be estimated using the following formulas. The exchangeable acidity is given at the bottom of the Penn State Soil Test Report (see Figure 1.2-3). Some soil testing labs report exchangeable acidity as “Exchangeable H+.”
- For a desired pH of 7.0, the lime requirement in lb CCE/A can be estimated as follows:
- Lime requirement = exchangeable acidity × 1,000
- For a desired pH of 6.5, the lime requirement in lb CCE/A is estimated as follows:
- If the exchangeable acidity is greater than 4.0, then:
- Lime requirement = exchangeable acidity × 840 or
- If the exchangeable acidity is less than 4.0 and the soil pH still less than 6.5, then:
- Lime requirement = 2,000 lb/A
- Otherwise, no lime is recommended.
The recommendation is based on liming an acre furrow slice approximately 7 inches deep, using a liming material that is 100% calcium carbonate equivalent (CCE) in neutralizing power and a material that is at least “fine sized” as defined by Pa. Aglime regulations (see Soil Acidity and Liming earlier in this chapter). If a liming material that is not near to 100 percent CCE (90- 110 percent CCE) is used, the rate must be adjusted for lime quality. Table 1.2-1 gives the details for making this simple but important adjustment. If the limestone will be mixed with a larger volume of soil (i.e., if the plow depth is more than 9 inches), the recommendation is adjusted as follows:
| Plow depth | Adjusted limestone requirement |
|---|---|
| Less than 9 inches | No adjustment |
| 9 to 11 inches | Basic requirement x 1.5 |
| More than 12 inches | Basic requirement x 1.8 |
See Agronomy Facts #3 Soil Acidity and Liming for details on limestone recommendations, liming material quality, and liming practices.