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TEST PROCEDURES & METHODS

For the best use of soil testing results, it is important to know the following:

  1. Laboratory method used for each analysis.
  2. Units reported for each analysis.
  3. Any conversion or calculation used for specific tests.

Actual nutrient availability in the soil is determined by changing factors including: soil moisture, temperature, pH, clay content, internal drainage, organic contact and physical barriers. As any of these factors change, the availability will also change.

For a printable PDF with all methods, click here.

SOIL

- All soil samples are dried and ground, except for soil microbial analysis.

Analysis

Units

Method Description

Soil pH

--

1:1 Soil/Water Slurry

Buffer pH (Buffer Index)

--

Sikora Buffer Method

Soluble Salts (EC)

mmhos/cm

1:1 Soil/Water Slurry

Potassium

ppm

Ammonium Acetate Extraction

Phosphorus, Bray 1

ppm

Bray 1 Extraction

Phosphorus, Olsen

ppm

Olsen Extraction, when soil pH >7.2

Calcium, Magnesium and Sodium

ppm

Ammonium Acetate Extraction

Sulfur

ppm

Monocalcium Phosphate Extraction

Copper, Iron, Manganese and Zinc

ppm

DTPA Extraction

Boron

ppm

DTPA Extraction

Nitrate-Nitrogen

lb/acre

CaSO4 Extraction, Chromotropic Analysis

Ammonium-Nitrogen

lb/acre

KCl Extraction

Organic Matter

%

Loss on Ignition (LOI), expressed as OM%



 

Soil test methods are described in:

  • Soil, Plant and Water Reference Methods for the Western Region. 2005 3rd Edition, WREP 125.

 

PLANT TISSUE

- All plant tissue samples are dried and ground.

Analysis

Units

Method Description

Total Nitrogen

%

Combustion

Minerals:

 

 

     P, K, S, Ca, Mg, Na

%

Nitric Acid/Hydrogen Peroxide Digestion

     Cu, Fe, Mn, Zn, B, Al

ppm

Nitric Acid/Hydrogen Peroxide Digestion

Nitrate-Nitrogen

ppm

Water Soluble

Phosphate-Phosphorus

ppm

Water Soluble

Plant tissue test methods are described in:

  • Plant Analysis Handbook. 2014, 4th Edition, Micro-Macro Publishing, Inc. Athens, GA.

           

MANURE

- All manure samples tested and reported “as received”.

Analysis

Units

Method Description

Dry Matter/ Moisture

%

Oven Drying at 85°C, 16 hours

Nitrogen (TKN)

%

Total Kjeldahl Digestion

Minerals:

 

 

     P, K, S, Ca, Mg, Na

%

Nitric Acid/Hydrogen Peroxide Digestion

     Cu, Fe, Mn, Zn

ppm

Nitric Acid/Hydrogen Peroxide Digestion

Ammonium-Nitrogen

%

Direct Distillation

Nitrate-Nitrogen

%

DeVarda's Distillation

Organic Nitrogen

%

Calculated: (TKN – Ammonium-Nitrogen)

pH

--

1:2 Manure:Water Slurry

Electrical Conductivity (EC)

mmhos/cm

1:2 Manure:Water Slurry

 

 Manure test methods are described in:

  • Recommended Methods of Manure Analysis. 2003, University of Wisconsin Extension Publication A3769