Fact Sheets And Publications
Using the Nutrient Management Fertility 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), ppm (Mn, Zn, S, B)|
|AgroLab||Mehlich 3||ppm, UD-FIV (for P only)|
|Brookside Laboratories, Inc||Mehlich 3
Bray 1 P
Ammonium acetate K
|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
Bray 1 P
Ammonium acetate K
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.
- Mehlich 1 soil extract
- Mehlich 3 soil extract
- Bray P1 (P), ammonium acetate (K, Ca, Mg), hydrochloric acid (HCl; Mn, Zn) soil extracts
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||Water (1:1)||Adams-Evans|
|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 Agricultural Laboratories, Inc.||Water (1:1)||Adams-Evans (KY location); Mehlich (NC location)|
|Waypoint Analytical||Water (1:1)||Mehlich; SMP (by request only)|
Adams-Evans buffer lime requirement tables
Commercial Agriculture Soil Test Notes
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