Soil Test Interpretation Sheet
+
To calculate Sodium Adsorption ratio use the following formula. All units in meq/L: ( )= √ +2 +
Table 3. Minimum Levels for Sustainable Nutrition and Sufficiency Level of Available Nutrients macronutrient guidelines for soil test interpretation. Nutrient Extraction Solution SLAN (ppm) 1 MLSN (ppm) 2 Phosphorus Mehlich III 27 – 54 21 Bray P1 15 – 30 Olsen 12 – 28 Potassium Mehlich III 50 – 116 (sand) 37 (all) Mehlich III 75 – 176 (others) Calcium Mehlich III 500 – 750 331 Magnesium Mehlich III 60 – 120 (sand) 47 (all) Mehlich III 70 – 140 (others) Sulfur Mehlich III 15 – 40 7
+2
2
+
( )=
+2 +
+2
√
2
Example: A saturated paste extract test result reports the following: Na + = 1,000 ppm Ca +2 = 200 ppm Mg +2 = 100 ppm 1. Convert ppm to meq/L.
Na + = 1,500 ppm /23 = 44 meq/L Na Ca +2 = 300 ppm/20 = 10 meq/L Ca Mg +2 = 150 ppm/12.2 = 8.2 meq/L
1 Carrow et al. 2003b 2 Woods et al. 2016
44 √10+8.2 2
2. Place values into SAR equation: 14.6 =
44 √10+8.2 2
Table 4. Micronutrient guidelines for soil test interpretation.
3. Reference Table 1 to determine potential sodium hazard.
Nutrient
Acceptable 1
Test
Mehlich III, Bray-P1, and Olsen Mehlich III, Bray-P1, and Olsen procedures describe the amount of plant-available nutrients on soil exchange sites. Compared to a SPE test, these procedures better describe total soil nutrient reserves. Two methods of interpretation are outlined below. Sufficiency Level of Available Nutrients (SLAN) – Use SLAN as a minimum threshold to determine if soil test nutrient values are adequate to support plant growth. Values were originally developed as a guideline for crop nutrition; however, have been successfully applied to guide turfgrass nutrition. A fertilizer application should be considered when soil test values fall below the ranges indicated below. See Table 3 for SLAN guidelines . Minimum Levels for Sustainable Nutrition (MLSN) – Use MLSN as a minimum threshold to determine if soil test nutrient values are adequate to sustain healthy turf growth. Developed in 2014 by Pace Turf and the Asian Turfgrass Center following analysis of >3,500 soil samples which supported healthy turf, had pH values between 5.5 – 8.5, and a total exchange capacity of <6 meq/100 g. See table 3 for MLSN guidelines.
Iron
50 - 100
Mehlich III Mehlich III
Manganese
4 to 6 (pH < 7) 8 to 12 (pH > 7)
Zinc
1 to 2
Mehlich III Mehlich III
Copper
0.3 to 2.5
Boron
1 to 1.5
Saturated Paste Extract
1 McCarty, 2005
References Bray, RH and LT Kurtz. 1945. Determination of total, organic and available forms of phosphorus in soils. Soil Sci., 59:39-45. Carrow, RN, L Stowell, W Gelernter, S Davis, RR Duncan, J Skorulski. 2003a. Clarifying soil testing: I. Saturate past and dilute extracts. Golf Course Management, September 2003. pp. 81-85. Carrow, RN, L Stowell, W Gelernter, S Davis, RR Duncan, J Skorulski. 2003b. Clarifying soil testing: III. SLAN sufficiency ranges and recommendations. Golf Course Management, January 2004. pp. 194-198.
McCarty, LB. 2005. Best Golf Course Management Practices. Pearson Education, Inc., Upper Saddle River, New Jersey. Mehlich, A. 1953. Determination of P, K, Na, Ca, Mg, and NH4 soil test Div. Memo. NC Dept. Agric., Raleigh, NC 1953. Mehlich, A. 1978. New extractant for soil test evaluation of phosphorus, potassium, magnesium, calcium, sodium, manganese, and zinc. Commun. Soil Sci. Plant Anal., 9(6): 477-492. Mehlich, A. 1984. Mehlich 3 soil test extractant: A modification of Mehlich 2 extractant. Commun. Soil Sci. Plant Anal. 15:1409-1416.
Olsen, SR, CV Cole, FS watanabe, and LA Dean. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA circular 939. U.S. Govt. Printing Office, Washington, DC. Woods MS, Stowell LJ, Gelernter WD. 2016. Minimum soil nutrient guidelines for turfgrass developed from Mehlich III soil test results https://doi.org/10.7287/peerj.preprints.2144v1
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