Michigan State University Extension
Soils & Soil Management - Fertilizer - 06029706
07/10/97
Fertilizer Recommendations for Field Crops in Michigan Extension Bulletin E-550A, March 1992
D. R. Christenson, D. D. Warncke, M. L. Vitosh, L. W. Jacobs and J. G. Dahl, Department of Crop and Soil Sciences
Mineral Soils. Soil reaction is expressed as pH. A soil having a pH of 7.0 is neutral-neither acid nor alkaline. A soil having a pH of 6.0 is mildly acid; pH 5.0 is strongly acid, while pH 8.0 is mildly alkaline.
Nutrients are most available in mineral soils having a pH between 6.0 and 7.0. For general field crops it is recommended that acid soils be limed to pH 6.0-6.5. If alfalfa is being established, lime the soil to pH 6.8.
The lime requirement of acid soil samples submitted to the MSU Soil Testing Laboratory is determined by measuring the total acidity. The total acidity is composed of both soluble and exchangeable aluminum and hydrogen. This method of determining lime requirement is more precise than estimates made from soil pH measurements alone, because it measures total acidity instead of just active acidity of the soil. The degree of acidity is reported as the "lime index." Lime requirement for mineral soils based on lime index is given in (Vis. 2).
When the lime requirement is less than one ton per acre, applying lime is of questionable value because of the difficulty of uniform spreading and the economic value. When the lime requirement is less than 1 ton, the soil pH is usually adequate for optimum crop production. Retest these soils in two to three years to determine lime needs.
Do not apply more than 6 tons of lime per acre in any one season. Applying more may cause localized zones of high alkalinity, reducing the availability of essential nutrients. Retest soil with a lime index of 6.4 or below two years after application to determine if more lime is needed. When the lime need is greater than 4 tons per acre, apply the lime in a split application - i.e., half before plowing and half after plowing, more effectively neutralizes the acidity in the plow layer than one large application.
For potatoes, the soil is generally limed to pH 6.0. If there is no history of scab, or if it is not suspected because resistant varieties are grown, consider liming to pH 6.5. Do not exceed 2 tons of lime per acre at any one time. Apply lime following potato harvest, but not later than the fall prior to planting potatoes.
Lime practices need special attention under no-till crop production where nitrogen is applied to the surface of the soil. Surface applied nitrogen can cause the surface to become acid very quickly. This condition is not detected in a sample taken to the usual 8-10 inches. In this case take a sample from the top 2 inches in addition to the standard sample depth. An acid surface can reduce the effectiveness of triazine herbicides.
See Extension Bulletins E-471 and E-1566 for further information.
Organic Soils. Field crop production does not benefit from liming organic soils unless the soil pH is below 5.3 (1:2 soil: water suspension).
In some cases, the surface layer of soil may have a pH around 5.5, but the subsoil will have a much lower or higher pH. If the soil is plowed to a sufficient depth to bring some of the subsoil to the surface, the plow layer soil pH and lime requirement will change. Therefore, lime according to a soil test on a sample taken after plowing.
Problem areas in some fields may be due to acid or alkaline layers in the rooting zone. In newly established fields and problem areas, check the soil pH at 6-inch intervals to a depth of 2 to 3 feet to determine pH variations.
Lime recommendations for organic soils are based on soil pH rather than lime index. (Vis. 2) gives the lime recommendations for organic soils below pH 5.3.
| Visual title - Visual size | Visual title - Visual size |
|---|
| Limestone needed to raise soil pH of mineral soils - 61K |
