Fertilizer Recommendation Program

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• Crop and Field Information
• Soil Test Information
• The Fertilizer Recommendation Program Report

Crop and Field Information

Enter information about your soil, management, and crops that will be important for making the correct nutrient and lime recommendations.

Field ID and Date

Provide a field identifier and the date the soil sample was collected. These values will be included on the recommendation report for your reference only. No information you enter into the tool is collected or stored by MSU.

Soil Type

Indicate whether the soil is a mineral soil (loam, sandy, clay, etc.) or an organic (muck) soil.

Acres

The number of acres represented by the soil sample, which will appear on the recommendation report for your reference only.

Tillage 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 tillage 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 soil will not be moldboard plowed within two years of the lime application and the lime will be incorporated with a disk, chisel plow, or similar equipment, indicate tillage 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 tillage 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 requirement.

Crop Type and Current Crop

Choose the crop type (Field Crop, Vegetable, Fruit, Grass/Ornamental, or Shrubs & Flowers) and select the crop you would like recommendations for from the drop-down menu. Crops are listed alphabetically within each category. The 3-digit number next to each crop is a unique identifier used by the MSU Soil and Plant Nutrient Laboratory (SPNL) database.

Yield Goal

The yield that the grower seeks to attain on that field. For field crops and vegetables, the program will automatically populate this entry field with an average yield goal value for the chosen crop, as well as display the range of yield goals considered by the tool for reference. Yields outside of this range cannot be entered. If your yield goal is above the included range, enter the highest value listed. 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.

Previous Crop

The last crop that was grown in the field. Some previous crops, particularly legumes, will trigger a nitrogen credit in the program for the following crop. The tool assumes a fixed nitrogen credit for some crops like soybean (25 lb N/acre credit) and dry edible beans (20 lb N/acre credit). For other previous crops, the nitrogen credit is determined by a formula that considers percent stand. For example, a nitrogen credit from clover is calculated as [40+(0.5 times percent stand)] where over 5 to 6 plants/square foot in an established field is considered to be a 100 percent stand. If percent stand is not indicated, 25 percent is assumed and a conservative nitrogen credit of 52 lb/acre [e.g. 40 + (0.5 x 25)] is given. The formulas used by the program for various previous crops can be found in Table 5 in Extension Bulletins E2904 and E2934 (Link). Note that these are general estimates and not all potential nitrogen credits from previous cash crops and cover crops are considered by the tool. The nitrogen credit is reflected in the nitrogen recommendation given in the report.

Manure has been or will be applied prior to planting a crop?

For field crops and vegetables only. Select “Yes” or “No” to indicate whether or not manure has been, or will be, applied to the field. When “Yes” is selected a footnote will be included in the fertilizer recommendation report explaining that a credit should be taken for the nitrogen, phosphorus, and potassium added in the applied manure. The credits will depend on the type, form, timing, and rate of the manure being applied. No credits or adjustments are actually included in the nutrient recommendations provided in the report. If no data is provided about manure application, the program will default to “No.”

Price of N ($/lb); Price of Corn ($/Bu); and Irrigated?

For corn only. Information entered in these fields is used to calculate a nitrogen recommendation for corn that provides for the maximum economic return on investment in N fertilizer (MRTN). This N recommendation takes into consideration the yield potential, N:corn price ratio, irrigation availability (yes/no), and previous crop (corn, soybean, or small grain). For more detailed information and calculations on corn MRTN recommendations in the Corn Belt, visit the Corn Nitrogen Rate Calculator.

Blueberry Plant Age

For blueberry only. The age (in years) of the blueberry planting.

Soil Test Information

Enter soil test results obtained from a certified soil testing laboratory. The accuracy of nutrient and lime recommendations will depend on the quality and compatibility of the data provided.

The first step is to collect a good, representative soil sample. More information on proper soil sampling can be found in “Sampling Soils for Fertilizer and Lime Recommendations,” MSU Extension Publication E0498.

The MSU Fertilizer Recommendation Program is built off the database and recommendation algorithms of the MSU Soil and Plant Nutrient Laboratory (SPNL), and is therefore optimized for the analytical procedures used by the SPNL. That said, soil test results from most certified soil testing laboratories can be used to obtain accurate MSU recommendations with the tool as long as the procedures used are compatible and appropriate corrections (where necessary) are applied.

The MSU SPNL uses soil testing procedures recommended by the North Central Region Committee on Soil Testing and Plant Analyses (see NCR Pub. 221), which are noted for each nutrient below. In contrast to these methods, many commercial soil testing labs now use the Mehlich-3 “universal” extractant for determining the availability of P, K, Ca, Mg, and other plant-essential nutrients. While Mehlich-3 results are highly correlated with the values obtained by the standard SPNL methods, in some cases applying a conversion factor [https://ohioline.osu.edu/factsheet/anr-75] to raw Mehlich-3 values before entering them into the Fertilizer Recommendation Program may improve the accuracy of recommendations, most notably for phosphorus (see below). Soil testing labs may also already apply such a conversion before reporting the results to you. Therefore, you may need to contact your soil testing lab to clarify the methods they use and how values are reported. If your soil test came from the MSU SPNL, no conversions are needed.

A note about units

The MSU Fertilizer Recommendation Program accepts P, K, Ca, Mg, and micronutrient soil test values reported in parts per million (ppm). Most soil testing labs now report results as ppm. In the event that soil test results are reported in lb/acre instead, you can convert them to ppm before entering them into the tool. For mineral soils, 1 ppm is equal to approximately 2 lb/acre of soil to a depth of 6 2/3 inches. Therefore, values in lb/acre can be divided by 2 and entered as ppm. For organic soils, assuming a bulk density of 0.66 grams per cubic centimeter, 1 ppm equals 1 lb/acre, and no conversion would be needed.

Soil pH

Soil pH provides an indication of the level of active soil acidity or alkalinity. This measurement, sometimes referred to as the water pH, is generally determined on a 1:1 soil:distilled water mixture by volume. Values above 7.0 are alkaline, 7.0 is neutral, and values below 7.0 are acidic. The optimum pH varies by crop, but on mineral soils a pH between 6.0 and 6.5 is typically desirable. However, alfalfa, for example, grows best at pH 6.6 - 7.2. For organic (muck) soils, the target pH generally ranges from 5.3 to 5.8, depending on crop.

Lime Index

The lime index provides an indication 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.

The lime index is determined in the lab by adding SMP (Shoemaker, McLean, Pratt) buffer solution to a 1:1 soil:water slurry and measuring the resulting pH. Some labs will report this value directly as the “buffer pH.” In general, lime index = buffer pH x 10, (e.g., a buffer pH of 6.7 on a commercial soil test report can be entered into the Fertilizer Recommendation Program as a lime index of 67).

Soils with greater reserve acidity have a higher capacity to resist change in pH. Therefore, clay soils which have high levels of reserve acidity require more lime to bring about a 1.0 pH unit change than do sandy soils which have lower levels of reserve acidity. Hence, a clay loam soil and a sandy loam soil with the same soil pH will have different "lime indexes" and lime needs.
For more information on liming, see MSU Extension Bulletins E-471, Lime for Michigan Soils, and E- 1566, Facts About Lime.

Phosphorus (P) and P Test Method

The MSU SPNL measures an index of available P using the Bray-Kurtz P1 (weak acid) test. Most commercial labs now measure P using the Mehlich-3 extractant, although results are often reported as “Bray-P1 equivalent” values. On soils with free calcium carbonates, the Bray-Kurtz P1 extraction is less effective. The Olsen test (0.5 N sodium bicarbonate) provides a better indication of P availability on calcareous soils with pH above 7.2 and a Bray-Kurtz P1 test of less than 10 ppm.

Getting the right P fertilizer recommendations from the tool requires indicating the correct P test method. Select “Bray P1/Mehlich” if the soil test results came from either of these methods (most common). If Mehlich-3 values are reported as “Bray-P1 equivalent” they can be entered into the tool without any correction. However, if raw Mehlich-3 values are reported, first divide by 1.35 [https://ohioline.osu.edu/factsheet/anr-75] to convert to Bray-P1 equivalent before entering into the tool. Mehlich-3 P values tend to be about 35 percent higher than Bray P1 values. Select “Olsen” if your values came from the Olsen test (less common, based on specific conditions above). You may need to contact your soil testing lab to clarify the methods they use and how values are reported.

In general, P test levels less than 10ppm are very low, 20-30 ppm are medium and above 50 ppm are very high for most field crops grown on mineral soils. Many vegetables require higher levels of available P so that a soil test of 50-75 ppm may be more desirable.

Potassium (K), Magnesium (Mg), and Calcium (Ca)

The MSU SPNL measures an index of available K, Mg, and Ca by extraction with 1 N neutral ammonium acetate. Most commercial labs use the Mehlich-3 extractant, although soil test results may already be reported as ammonium acetate equivalent values using regressions developed by the lab. If raw Mehlich-3 values are reported, conversion factors are available for K, Mg, and Ca [https://ohioline.osu.edu/factsheet/anr-75] to correct values before entering into the tool. However, the differences between the two methods, particularly for K, are much smaller than for phosphorus and could be considered negligible.

Potassium (K) test values of less than 30 ppm are very low for most field crops, 80 to 105 ppm are medium and above 150 ppm are very high. For many vegetables, a potassium test level of 140 to 150 ppm may be desired.

Magnesium (Mg) levels are considered inadequate for most crops when any of the following conditions exist:

• Soil test values are less than 35 ppm on sandy soils, less than 50 ppm on fine-textured soils, or less than 75 ppm on organic (muck) soils.
• Magnesium accounts for less than 3 percent of the total exchangeable bases (Ca + Mg + K, on an equivalence basis).
• Relative to the total bases content (percent bases), the magnesium percentage is less than the potassium percentage.

Calcium (Ca) levels are generally adequate in Michigan soils. Even acid soils needing lime generally contain sufficient calcium for plant growth. This test value is used primarily to calculate nutrient balances and in making magnesium recommendations.

Zinc (Zn), Manganese (Mn), Copper (Cu), and Boron (B)

Analyses of these micronutrients generally need to be requested in addition to the standard soil test. The MSU SPNL measures an index of Zn, Mn, and Cu by extraction with either 0.1 N (Zn, Mn) or 1.0 N (Cu) hydrochloric acid. DTPA is used as an alternative extracting solution for Cu, Mn, and Zn, especially for calcareous soils. The hot water extraction procedure is used for boron (B). Again, most other commercial labs use the Mehlich-3 extractant for these nutrients, although soil test results may be reported as equivalents to the SPNL standard methods using regressions developed by the lab. If uncorrected Mehlich-3 values are reported, using these values in the tool may result in lower than expected fertilizer recommendations (since the Mehlich-3 solution tends to extract more of the nutrients than the other extractants). Broadly accepted conversion factors for these nutrients are not currently available.

Adequate levels of Zn and Mn vary with the crop and soil pH. Deficiency of Mn is most likely to occur above pH 6.5. Deficiency of Zn is most likely above pH 7.0. For most crops, a Mn level of 20 ppm is sufficient and less than 10 ppm is inadequate. A Zn level of 10 ppm is sufficient and less than 2 ppm is inadequate. Sufficiency in between these levels depends on the crop and the soil pH. As soil pH increases, higher Mn and Zn soil test levels are required in order to provide sufficient amounts for optimum plant growth. Copper (Cu) levels are adequate (above 0.5 ppm) in most Michigan mineral soils. Copper deficiencies are most likely on newly developed organic soils.

For more information on interpretation of soil test nutrient levels and nutrient management, see the following MSU Extension Bulletins:

• E2904: Nutrient Recommendations for Field Crops in Michigan
• E2934: Nutrient Recommendations for Vegetable Crops in Michigan

The Fertilizer Recommendation Program Report

The soil test information entered in the tool appears in the “Soil Nutrient Levels” and “Additional Results” sections of the Fertilizer Recommendation Program Report. In addition, a graphical representation of the nutrient status for P, K, and Mg is provided, in addition to calculated CEC and percent exchangeable base values, as explained below.

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. CEC is calculated by adding together the amount of soil test values of potassium, calcium, magnesium, and hydrogen held on the soil particles. It is expressed in milliequivalents per 100 grams of soil. Loamy sands and sands usually have a CEC less than 8. The CEC of sandy loams frequently falls between 8 and 12. Loams, clay loams and clays usually have a CEC greater than 12. 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.

Percent 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. Mg should be above 3 percent and greater than the percentage of K. For example, 6.8 percent K and 4.2 percent Mg indicates a Mg-deficient soil situation.

The “Recommendations” section provides lime and crop nutrient recommendations based on the crop and soil test information provided.

Lime

When lime is required to neutralize excess soil acidity, the lime recommendation includes two pieces of information. First, the target pH to which the soil should be increased by liming is provided. This is dependent on the soil type and crop being grown. For most field and vegetable crops on mineral soils, pH 6.5 will be indicated, but when alfalfa is grown for example, pH 6.8 will be indicated. Next, the tons of lime required to achieve this pH is provided, which is calculated based on the entered starting pH and lime index of the soil and the tillage depth. Tillage depth will be printed only if a value was entered; if nothing is printed, a 9 inch tillage depth was used in calculating the recommendations. Additional recommendations regarding lime applications may appear in the footnotes/messages provided at the bottom of the report.

Major Nutrients

Alongside the chosen crop and expected yield, nutrient recommendations are given for the major macronutrients (N, P, and K) in lb N/acre (for nitrogen), lb P2O5/ac (for phosphorus) and lb K2O/ac (for potassium). Commercial fertilizer percent nutrient analyses are similarly reported in these terms. The nutrient rate recommendations given are those that will result in the most economical yields. This of course assumes that the soil sample is representative, that a realistic yield goal has been chosen, that average weather prevails, and that good management practices are used. However, due to variations in these factors, the most economical fertilizer rates may vary from those given.

Secondary Nutrients

Magnesium (Mg) is the only secondary nutrient for which a recommendation is given on the recommendation report. The need for Mg is indicated by one of two footnotes at the bottom of the report: 1) "Magnesium tests low, use dolomitic limestone," or 2) "Magnesium tests low, broadcast 50-100 lb Mg/acre or row apply 10-20 lb Mg/acre.” The first footnote is printed when lime is required to neutralize excess soil acidity. The second footnote is printed when the magnesium test is low but the soil pH is adequate so that no lime is needed.

Micronutrients

The micronutrients for which recommendations are provided by the tool are zinc (Zn), manganese (Mn), copper (Cu) and boron (B). Recommendations for Zn, Mn, and Cu are based on crop response, soil pH, and soil test level. No recommendation will be given for these three micronutrients without a soil test value. Boron is recommended based on crop response, soil texture, and soil pH. Recommendations are given as pounds of element per acre for each of the micronutrients, and commercial fertilizers are similarly labeled according to the percent of a micronutrient contained.

Footnotes/Messages

Footnotes appear at the bottom of the report in special situations to provide additional information or to help you better understand the recommendations and maximize crop production through proper management.

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, sidedress, and foliar applications. Given the many ways a farmer can supply the nutrients in the recommendation, consider working closely with your local Cooperative Extension educator, consulting agronomist/horticulturist, and/or fertilizer dealer to determine the most suitable fertilization program for your farming operation.

To learn more on your own, see these Additional Resources from MSU Extension.

To find additional assistance with the tool, interpreting your soil test report, or with lime/nutrient/fertilizer management on your farm see the Help page to connect with MSU Extension educators and specialists.

 The information in this guide was adapted for the MSU Fertilizer Recommendation Program from Understanding the MSU Soil Test Report by Dr. Darryl Warncke.