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The Anatomy of a Soil Test Report


March 10, 2023 - Author: and Christine Charles,

Adapted from D.D. Warncke, J. G. Dahl and M. L. Vitosh's "Understanding the MSU Soil Test Report" (2016) by Christine Charles and Christina Curell, Michigan State Extension Educators

The Background

The background information is already provided by the farmer before submitting samples. Consider providing the following information if possible when sending your samples to receive helpful footnotes and accurate fertilizer recommendations when getting test results back:

  • Plow Depth - the depth (inches) to which limestone will be incorporated if lime is needed. Listing the wrong depth could result in too much or too little lime being recommended. If information on “plow depth” is not given, 9 inches is used to determine the lime requirement.
    • When lime is spread and incorporated with a moldboard plow, the depth indicated should be the depth of plowing.
    • When the lime will be incorporated with a disk, chisel plow or similar equipment, indicate “plow depth” as only one-half of the implement’s working depth in the field. That’s because such tillage tools effectively incorporate surface broadcast materials to only one-half the depth of tillage.
    • For no-till systems, list two inches as the “plow depth” since limestone is not incorporated and will not appreciably alter the soil pH at depths greater than two inches. Where continuous no-till is being used for crop production, a second soil sample should be taken to a two-inch depth for determining pH changes near the surface and the appropriate lime need.
  • Previous Crop - the last crop which was grown in the field. When beans, alfalfa, or clover is the previous crop, a nitrogen credit is given. The nitrogen credit equals [40+(.60 times percent stand)] where over 5 to 6 plants/square foot in an established field is a 100 percent stand. If percent stand is not indicated, 70 percent is assumed and a nitrogen credit of 80 lb/acre [e.g. 40 + (.6 x 70)] is given. The nitrogen credit is reflected in the printed nitrogen recommendation.
  • 1st Crop: 2nd Crop - the next two crops to be grown (in sequence) or two crop options which may be grown. Fertilizer and lime recommendations are given for each crop but apply lime only once.
  • Yield Goal - the yield which the grower seeks to attain on that field. Yield goal is best based on a five-year yield average, not a highest one year yield. When figuring the yield average over several years, do not include unusually high or low yields. If a yield is not indicated by the farmer, the computer will select an average yield for that soil management group.

Soil Test Results

Soil pH - the level of soil acidity or alkalinity. Above 7.0 is alkaline, 7.0 is neutral and below 7.0 is acidic. This measurement, sometimes referred to as the soil water pH, is made with soil in distilled water. A pH between 6.0 and 6.8 is best for production of most field crops.

Lime Index - an indicator of the reserve or potential acidity in soil and is used to determine the quantity of lime needed to correct the pH of an acid soil. Lime index measurements are made only on samples testing less than pH 6.8. The lime index usually falls between 70 and 60. With a lime index above 70, no additional lime is needed. As the lime index decreases below 70, more lime is required to bring the pH back up to 6.5.

Soil test phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) values are reported in parts per million (ppm). For mineral soils, 2 lb/acre equals 1 ppm (parts per million). To interpret how specific ranges relate to your management goals and crop, contact your local extension agent or read "Understanding the MSU Soil Test Report" E-0015. Nitrogen (N) is not measured in this test despite being an essential macronutrient. As a dynamic nutrient with various pathways of movement, N content changes quickly; accurate testing requires immediate freezing and is an expensive process. Therefore, N recommendations are based on research, organic matter content, cropping history, and crop needs.

Organic Matter - is reported as percent of active organic matter in the soil. The active rather than the total organic matter content is reported because this part is important in nutrient holding and the adsorption of herbicides. Most mineral soils in Michigan have active organic matter contents between 1 and 4 percent and vary based on soil texture.

Cation Exchange Capacity (CEC)- an indicator of the nutrient holding capability of a soil. It is a relatively permanent characteristic of each soil and is not easily changed. In general, the greater the clay and organic matter contents, the higher the CEC of a soil. As the soil pH changes, the CEC value will also vary somewhat. The higher the CEC, the greater the capacity of the soil to hold nutrients and bind certain pesticides. The CEC of a soil is also important in determining permissible heavy metal loading rates associated with land application of sewage sludge.

% of Exchangeable Bases- information on the nutrient balance among potassium, calcium and magnesium. The percentages reported assume K, Ca and Mg comprise 100 percent of the exchangeable bases, and are used to determine potential magnesium deficient situations.

Fertilizer Recommendations & Footnotes

Fertilizer recommendations are based on the soil test results and crop information provided. Recommendations are given in pounds of N (nitrogen), P2O5 (phosphate) and K2O (potash) for the major nutrients and in pounds of element per acre for each of the micronutrients. Commercial fertilizer analyses are similarly reported as percent of the element present. When the cropping information is provided, fertilizer recommendations are given for two crops. These may be for a two crop sequence or two alternative crops. The nutrients recommended can be supplied from a wide variety of fertilizer materials and applied through various combinations of pre-plant broadcast, planting time band and side dress applications. Since many ways are available for a farmer to supply the nutrients in the recommendation, it is suggested that the farmer work closely with the local MSU Extension Service agricultural educator, a consulting agronomist, or horticulturist, and/or a fertilizer dealer to determine the most suitable fertilization program for their farming operation.




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