Nutrient Recommendations

A blue tractor spraying / applying nutrients to a field.

Nutrient Recommendations

 

Nutrient recommendations are based upon soil test calibration studies that relate the probability of a profitable plant response to nutrient addition to the plant nutrient concentration in the soil as measured by a soil test.

Review the "Using the nutrient recommendations" below and then select an crop type to view a PDF with individual recommendations.

USING THE NUTRIENT RECOMMENDATIONS

 

Converting from Soil Test Results to University of Delaware Fertility Index Value (FIV)


Nutrient recommendations are based upon soil test calibration studies that relate the probability of a profitable plant response to nutrient addition to the plant nutrient concentration in the soil as measured by a soil test. However, the concentration of a soil nutrient measured by a specific soil test extracting solution is a function of the chemical composition of extracting agent and the forms of the nutrient present in the soil. Consequently, the concentration of a plant nutrient measured on a soil sample will vary with the soil test extracting solution used.

University of Delaware Nutrient Recommendations are based on the Mehlich 3 soil test. The University of Delaware Soil Testing Program reports results for phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) as a Fertility Index Value (FIV). Results for manganese (Mn), zinc (Zn), sulfur (S), and boron (B) are reported in pounds per acre (lb/ac). Other regional soil testing laboratories may use different soil test extractions or report results in different units (Table 1).

 

Table 1. The most common soil tests used by laboratories that analyze samples from Delaware and the Delmarva Peninsula.
Laboratory Soil Test Method Reporting Units
University of Delaware (UD) Mehlich 3 UD-FIV (P, K, Mg, Ca), lb/ac (Mn, Zn, S, B)
AgroLab Mehlich 3 ppm, UD-FIV (for P only)
Brookside Laboratories, Inc Mehlich 3
Bray 1 P
Ammonium acetate K
ppm
Penn State University Mehlich 3 ppm
Rutgers University Mehlich 3 lb/ac or ppm
Spectrum Analytical Laboratories Mehlich 3 lb/ac or ppm
Virginia Tech Mehlich 1 lb/ac
Waters Agriculture Laboratories, Inc Mehlich 1 lb/ac
Waypoint Analytical Mehlich 3
Mehlich 1
Bray 1 P
Ammonium acetate K
ppm

 

If available soil test results were obtained from a soil testing laboratory that uses a soil extract other than Mehlich 3 or that reports Mehlich 3 results in units other than UD-FIV (P, K, Ca, Mg ) or lb/ac (Mn, Zn, S, B), it is necessary to first convert those soil test values to the equivalent UD-FIV or Mehlich 3 equivalent in lb/ac before making a nutrient recommendation.

NOTE: Nutrient recommendations prepared using the University of Delaware Nutrient Recommendations from soil test results that were not properly converted to UD-FIV or Mehlich 3 (lb/ac) may be completely inaccurate. Inaccurate recommendations could result in under- or over-application of the required nutrient and subsequent loss of yield or unnecessary expense.

Conversion factors are available based on correlation studies between Mehlich 3 and the other extracts using 300 Delaware soil samples) in the following tables. NOTE: Some laboratories offer multiple extractants (e.g., Brookside, Waypoint). Confirm which soil test extractant was used with the soil testing laboratory before selecting a conversion table.

 

Calculating the Lime Recommendation

To determine the lime requirement for a field, follow these steps:

Select the appropriate lime table from the list below based upon the target pH of the crop as listed in the recommendation section.  Locate the value in the table where the Water pH row (shown along the left side of table) and the Buffer pH column (shown across the top of the table) intersect (see example).

Determine whether a lime credit is necessary. Lime credits are used to account for any lime that was applied in the past 18 months which has not had a chance to react. The equation for calculating the lime credit and an example can be obtained by clicking here.

Determine the the type of lime recommended (e.g., calcitic or dolimitic) by clicking here.

 

Writing a Lime Recommendation

Step-by-step instructions for writing a lime recommendation is available in Calculating the Lime Recommendation Using the Adams-Evans Soil Buffer.  If the lime requirement test was performed by laboratory using a different buffer pH method (Table 2), refer to Measurement and Management of Soil pH for Crop Production in Delaware.
 

Table 2. Methods for water and buffer pH tests used by regional soil testing laboratories.
Laboratory Soil pH Method Lime Requirement Method
University of Delaware (UD) Water (1:1) Adams-Evans
AgroLab Water (1:1) SMP
Brookside Laboratories, Inc Water (1:1) SMP/Sikora
Penn State University Water (1:1) Mehlich
Rutgers University Water (1:1) Adams-Evans
Spectrum Analytical Laboratories Water (1:1) Sikora
Virginia Tech Water (1:1) Mehlich
Waters Agriculture Laboratories, Inc Water (1:1) Adams-Evans (KY location); Mehlich (NC location)
Waypoint Analytical Water (1:1) Mehlich; SMP (by request only)

 

 

University of Delaware Lime Tables

These tables are designed to be used with the Adams-Evans buffer pH. If the lime requirement test was performed by laboratory using a different buffer method, contact the laboratory for the appropriate lime tables.

 

Commercial Agriculture Soil Test Notes

Related Fact Sheets


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  • DELAWARE GARDENER’S GUIDE TO SOIL PH

    Soil pH is a measure of soil acidity or alkalinity. On the pH scale a value of 7 is neutral, pH values less than 7 are acidic, and pH values greater than 7 are alkaline. Homeowners and gardeners are interested in soil pH because soil pH directly affects the growth and quality of many landscape plants.

  • FERTILIZER BASICS

    Proper fertilization will enhance plant growth without polluting the environment. However, misuse of fertilizer can harm the environment and injure landscape plants by causing fertilizer burn to leaves and/or roots.

  • HOW TO TAKE A SOIL SAMPLE?

    Soil tests such as those conducted by the University of Delaware Soil Testing Laboratory will help you to develop and maintain more productive soil by providing more information about the fertility status of your soil. This helps you to select the proper lining and fertilization program so that you can obtain optimal growth of lawn, garden and ornamental plants.

  • MEASUREMENT AND MANAGEMENT OF SOIL PH FOR CROP PRODUCTION IN DELAWARE

    The pH scale ranges from 0 to 14; a pH value of 7 is considered neutral, while pH values less than 7 are acidic, and pH values greater than 7 are alkaline. The pH values of soil usually range from pH 4.0 to pH 8.0; higher or lower pH values are very rare and are normally found only in severely disturbed soils or in soils that have been amended with some type of acidic or alkaline material.

  • NUTRIENT RECOMMENDATIONS

    Nutrient recommendations are based upon soil test calibration studies that relate the probability of a profitable plant response to nutrient addition to the plant nutrient concentration in the soil as measured by a soil test.

  • PHOSPHORUS MANAGEMENT STRATEGIES FOR DELAWARE’S AGRICULTURAL SOILS: THE PHOSPHORUS SITE INDEX

    Long-term use of fertilizer and manure nutrients on the Delmarva Peninsula has led to an enrichment of agricultural soils with phosphorus (P). Consequently, many soils in Delaware are now considered high or excessive in soil test P (Fig. 1). In some situations, high P soils contribute to eutrophication of surface waters; therefore, P management strategies that maintain both agricultural profitability and environmental quality are necessary. 

  • PHOSPHORUS REMOVAL BY DELAWARE CROPS

    In Delaware, applications of phosphorus to “high P” soils (soil test P ≥ 150 FIV, as defined by the Delaware Nutrient Management Commission) cannot exceed a three-year crop removal rate unless alternative P management strategies (i.e. N-based management during one or more years of a crop rotation) are permitted based on results of a P Site Index.

  • RECOMMENDED SOIL TESTING PROCEDURES FOR THE NORTHEASTERN UNITED STATES

    Northeastern Regional Publication No. 493
    3rd Edition- Agricultural Experiment Stations of Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and West Virginia. Prepared by: The Northeast Coordinating Committee for Soil Testing (NECC-1312)

  • SOIL MANAGEMENT OPTIONS BASED ON THE PHOSPHORUS SITE INDEX

    Minimizing nonpoint source pollution of surface waters by P from agricultural cropland requires management practices that control both the supply and transport of soil P. The basic objective of environmentally sound P management is to maintain soil P fertility levels in a range that is optimum, but not excessive, for crop growth while reducing the loss of particulate and soluble P by processes such as erosion, runoff, or drainage. 

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