Soil Parameter |
Test Method |
Potassium |
Potassium is extracted from soil by combining 1.5g soil with 15ml ammonium acetate extractant, which is then shaken for 5 minutes. The centrifuged extract is tested using an ICP spectrometer at 766.491nm. |
Phosphorus |
The Bray P1 extractant is used for neutral and acidic soils and Olsen extractant for alkaline soils. One gram of soil is shaken with 10ml of extractant for 5 minutes. The centrifuged extract is tested using an ICP spectrometer at 213.618nm. |
Nitrogen |
Nitrate nitrogen is extracted from soil by combining 5.0g soil with 25ml of a KCl solution and placing on shaker for 30 minutes. Nitrate is determined by reduction to nitrite using zinc dust, diazotized with sulfanilamide and is coupled to Napthyl-ethylenediamine to form a red-purple color, which is tested along with standards, using a spectrometer at 520nm. |
Calcium and Magnesium |
Same as for potassium, except that absorption is tested at 315.887nm and 285.213nm for calcium and magnesium respectively. |
Organic Matter |
Organic matter is tested using the Loss on Ignition method. A 2g sample of soil is placed in a crucible, and heated as 110'C for two hours. The initial weight of the crucible containing the soil is recorded. Then, the crucible is heated in a furnace at a temperature of 360'C for two hours, and then allowed to cool. The difference between the initial weight and the final weight is used to calculate the percentage organic matter. |
Soil pH Test |
We test soil pH by combining 12g soil and 12ml water and testing the mixture with a calibrated ph meter. |
Lime Requirement |
Lime requirements are determined using direct titration with lime. To three 1:1 mixtures of soil and water are added different amounts of lime. The mixtures are shaken for three hours and the final pH of each sample is measured. A curve is generated relating lime added to final pH, and the lime required to achieve a desire pH is derived from the curve. |
Soluble Salts |
Conductivity is using a 1:1 soil paste with distilled water. Results are presented as mS/cm. |
Metallic Micronutrients |
The metallic micronutrients are extracted by combining 10g of soil with 20ml of DTPA-AB extractant, and then shaken for 2 hours. The metal concentrations are tested using an ICP spectrometer which is set for the wavelength required for each metal. |
Sulfur |
A 1:2.5 mixture of soil and a solution of calcium phosphate monobasic are shaken for 30 minutes. The centrifuged extract is tested using an ICP spectrometer at 182.034nm. |
Boron |
Boron is tested using the hot water extraction method. Ten grams soil is mixed with 20 ml of a 0.1% solution of CaCl2 and boiled gently for 5 minutes. The centrifuged extract is tested using an ICP spectrometer at 208.956nm. |
Texture |
Texture is measured using the hydrometer method. Briefly, 50 grams of soil is dried, ground and sifted through a 2 mm sieve to separate the gravel fraction. Then the finer fraction is thoroughly mixed with 1000 ml of a dilute sodium hexametaphosphate solution in a sedimentation cylinder. The soil particles gradually settle to the bottom of the cylinder. The density of the solution is measured using a Bouyoucos hydrometer at 40 seconds and 2 hours to determine the silt and clay content of the soil. The sand content is determined by subtraction.
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Heavy Metal Screening |
The metals are extracted from the soil using a mixture of dilute mineral acids heated to 80'C for three hours. The extract is centrifuged and tested using an AA spectrometer at to determine lead and cadmium concentrations. The arsenic concentration is determined using the Hach Company colorimetric arsenic test.
Please note that we do not use the official EPA methods to test for heavy metals. The EPA methods are laborious and expensive to perform and impractical for ordinary screening purposes. We believe that our methods give results that are sufficiently accurate to provide a good indication of whether heavy metals are present in the soil at above normal levels.
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