Soil Analysis Application Package for Cannabis

Procedures for Soil Extractions and Analysis for PO₄-P, NO₃-N, K*, Ca, Mg, pH and Conductivity

Cannabis cultivation requires precise nutrient management to ensure optimal growth and yield. This application note provides detailed procedures for soil extractions and analysis of key nutrients such as phosphorus (PO₄-P), nitrogen (NO₃-N), potassium (K)*, calcium (Ca), magnesium (Mg), pH, and conductivity. By following these procedures, cultivators can accurately assess soil nutrient levels and make informed decisions to optimize their cannabis crops.

Summary Table

Extractant	Analyte(s)
Mehlich 2	Phosphorous, Magnesium, Calcium
Mehlich 1	Potassium *(Kit PN 2460000)
Calcium Sulfate	Nitrate-Nitrogen
Aqueous Extraction	Conductivity and pH

Soil Extractions

Mehlich 2 Extraction for Soil (Calcium + Magnesium and Phosphorus)

The Mehlich 2 soil extractant is used for extracting calcium and magnesium and phosphorus from soils. It is suitable for all classes of soils. With highly calcareous soils, calcium and magnesium results will be artificially high.

Before extraction, dry the soil sample, then screen it to a fineness of 0-2 mm using the Hach Soil Sieve. Careful preparation is important to assure volumetric measurement of the soil sample.

Reagents:

• 2266349 = Mehlich 2 Soil Extractant, 500-mL
• 27200 = DI water, 3.78 L (or equivalent)

Apparatus:

• 1862400 = Round Mixing Bottle, 25-mL
• 590900 = Polyethylene Bottle, 200-mL
• 591200 = Sprinkler with Screen (flip cap for bottle)
• 217240 = Graduated Cylinder, 25-mL
• 50658 = Circular Filter Paper, 100/pk
• 2415582 = Polyethylene Funnel, 82-mm
• 2657202 = Soil Scoop, 2-gram
• 4615900 = Soil Sieve

Preparing the Mehlich 2 Extractant

1. Measure 20 mL of the Mehlich 2 Soil Extractant Concentration into a 25-mL graduated cylinder.
2. Transfer the extractant concentration to one of the flip-top dispensing bottle.
3. Add deionized water to the dispensing bottle until the volume reaches the bottom of the neck, ~200 mLs. Invert several times to mix.

Mehlich 2 Extraction Procedure

1. Using the 2-gram scoop, measure 1 scoop of the prepared soil sample into a round sample bottle.
2. Using the 25-mL graduated cylinder measure 20 mLs of the diluted Mehlich 2 soil extractant into the cylinder, and transfer to the sample bottle.
3. Repeat steps 1–2 for each soil sample being extracted.
4. Cap and shake the sample bottle for 5 minutes.
5. Using the plastic funnel and filter paper (fold the round filter paper in half twice forming a triangular shape). Open the filter in a manner that forms an inverted cone.
6. Filter the contents of the bottle into another round sample bottle.
7. Use this filtered extract for the calcium and magnesium and phosphorus analysis.

Mehlich 1 Extraction for Soil (Potassium method 10321)

Before extraction, dry the soil sample, then screen it to a fineness of 0-2 mm using the Hach Soil Sieve. Careful preparation is important to assure volumetric measurement of the soil sample.

Reagents

• Mehlich 1 Soil Extractant, 1000-mL (7 mL Sulfuric Acid and 41.7 mL Hydrochloric Acid diluted to 1 L with 27200 (DI Water))
• 27200 = DI Water, 3.78 L (or equivalent)

Apparatus

• 1862400 = Round Mixing Bottle, 25-mL
• 590900 = Polyethylene Bottle, 200-mL
• 591200 = Sprinkler with Screen (flip cap for bottle)
• 217240 = Graduated Cylinder, 25-mL
• 50658 = Circular Filter Paper, 100/pk
• 2415582 = Polyethylene Funnel, 82-mm
• 2657202 = Soil Scoop, 5-gram
• 4615900 = Soil Sieve

Preparing the Mehlich 1 Extractant

1. Measure 20 mL of the Mehlich 1 Soil Extractant Concentration into a 25-mL graduated cylinder.
2. Transfer the extractant concentration to one of the flip-top dispensing bottle.
3. Add deionized water to the dispensing bottle until the volume reaches the bottom of the neck, ~200 mLs. Invert several times to mix.

Mehlich 1 Extraction Procedure

1. Using the 5-gram scoop, measure 1 scoop of the prepared soil sample into a round sample bottle.
2. Using the 25-mL graduated cylinder measure 25 mLs of the diluted Mehlich 1 soil extractant into the cylinder, and transfer to the sample bottle.
3. Repeat steps 1-2 for each soil sample being extracted.
4. Cap and shake the sample bottle for 5 minutes.
5. Using the plastic funnel and filter paper (fold the round filter paper in half twice forming a triangular shape). Open the filter in a manner that forms an inverted cone.
6. Filter the contents of the bottle into another round sample bottle.
7. Use this filtered extract for the potassium analysis.

Calcium Sulfate Extraction for Soil (Nitrate-Nitrogen)

The Calcium Sulfate Extraction is used to extract nitrate-nitrogen from soils and can be used for all classes of soils.

Before extraction, dry the soil sample, then screen it to a fineness of 0-2 mm using the Hach Soil Sieve. Careful preparation is important to assure volumetric measurement of the soil sample.

Reagents

• 1232120 = Calcium Sulfate Powder, 20 grams
• 27200 = DI water, 3.78 L (or equivalent)

Apparatus

• 1862400 = Round Mixing Bottle, 25-mL
• 217240 = Graduated Cylinder, 25-mL
• 50658 = Circular Filter Paper, 100/pk
• 2415582 = Polyethylene Funnel, 82-mm
• 51100 = Measuring Spoon, 0.1-gram
• 2657205 = Soil Scoop, 5-gram
• 4615900 = Soil Sieve

Aqueous Extraction Procedure

1. Using the 5-gram scoop, measure 2 scoop of the prepared soil sample into a round sample bottle.
2. Using the 0.1-gram plastic spoon, add 1 level spoonful of Calcium Sulfate to the round sample bottle containing the sample.
3. Using the 25-mL graduated cylinder measure 20 mLs of DI water and transfer it to the round mixing bottle.
4. Repeat steps 1–3 for each soil sample being extracted.
5. Cap and shake each bottle vigorously for 1 minute.
6. Using the plastic funnel and filter paper (fold the round filter paper in half twice forming a triangular shape). Open the filter in a manner that forms an inverted cone.
7. Analyze this extract for nitrate-nitrogen within 2 hours. If this is not possible, then the extract may be refrigerated for 24 hours before analysis.

Aqueous Extraction Method for Soil (Conductivity and pH)

Use the Aqueous Extraction method to prepare the soil sample for conductivity and pH. The soil suspension does not need to be filtered to determine these parameters, the measurement can be made directly in the suspension.

Before extraction, dry the soil sample, then screen it to a fineness of 0–2 mm using the Hach Soil Sieve. Careful preparation is important to assure volumetric measurement of the soil sample.

Reagents

• 27200 = DI water, 3.78 L (or equivalent)

Apparatus

• 108041 = Polyethylene Beaker, 50-mL
• 217240 = Graduated Cylinder, 25-mL
• 2657205 = Soil Scoop, 5-gram
• 4615900 = Soil Sieve

Aqueous Extraction Procedure

1. Using the 5-gram scoop, measure 4 scoop of the prepared soil sample into a 50-mL beaker.
2. Using the 25-mL graduated cylinder measure 20 mLs of DI water and transfer it to the 50-mL beaker.
3. Repeat steps 1-2 for each soil sample being extracted.
4. Using the spatula, stir the contents of the beaker for 1 minute at 10-minute intervals over a 30-minute period.
5. After 30 minutes, use the prepared sample for the conductivity and pH measurements.

Note: Because conductivity is affected by small concentrations of KCl resulting from the pH determination, measure the conductivity of the sample prior to measuring pH.

Analytical Procedures

Phosphate-Phosphorus Method 10209

TNT843 (0.05-1.5 mg/L PO₄-P), TNT844 (0.5-5.0 mg/L PO₄-P) or TNT845 (2-20 mg/L PO₄-P)

Dilute the Mehlich 2 soil extraction solution down to one of the concentration ranges listed for PO₄-P reagent sets. For example, take 1 mL of sample and dilute it up to 25 mLs with DI water in a 25-mL graduated cylinder. Multiply the final concentration reading by 25 for the non-diluted concentration value. Multiply this example concentration value by 10 to correct for the soil extraction (20 mL / 2 g = 10). Ensure that the DR spectrophotometer is reporting as PO₄-P.

Nitrate-Nitrogen Method 10206

TNT835 (0.2-13.5 mg/L NO₃-N) or TNT836 (5-35 mg/L NO₃-N)

Dilute the Calcium Sulfate soil extraction solution down to one of the concentration ranges listed for NO₃-N reagent sets. For example, take 1 mL of sample and dilute it up to 25 mLs with DI water in a 25-mL graduated cylinder. Multiply the final concentration reading by 25 for the non-diluted concentration value.

Multiply this example concentration value by 10 to correct for the soil extraction (20 mL / 10 g = 2). Ensure that the DR spectrophotometer is reporting as NO₃-N.

Potassium Method 10321

Reagent Set: 2460000 (0.1-7.0 mg/L K)

Dilute the Mehlich 1 soil extraction solution down to one of the concentration ranges listed for potassium reagent sets. For example, take 1 mL of sample and dilute it up to 25 mLs with DI water in a 25-mL graduated cylinder. Multiply the final concentration reading by 25 for the non-diluted concentration value. Multiply this example concentration value by 5 to correct for the soil extraction (25 mL / 5 g = 5).

Calcium and Magnesium (Mg by difference)

Total hardness Method 8213

• Reagent set: 2448100 (100-4000 mg/L CaCO₃)
• Dilute the Mehlich 2 soil extraction solution following the Digital Titrator method and select the appropriate sample volume for the perceived concentration range. Multiply the concentration value by 10 to correct for the soil extraction (20 mL / 2 g = 10).

Calcium hardness Method 8204

• Reagent set: 2447500 (100-4000 mg/L CaCO₃)
• Dilute the Mehlich 2 soil extraction solution following the Digital Titrator method and select the appropriate sample volume for the perceived concentration range. Multiply the concentration value by 10 to correct for the soil extraction (20 mL / 2 g = 10).

pH Method 8156

(0 – 14 pH Units)

• Direct measurement using the aqueous soil extraction solution, see the Aqueous Extraction Procedure above for more information.

Conductivity Method 8160

(0.01 μS/cm – 200 mS/cm)

• Direct measurement using the aqueous soil extraction solution, see the Aqueous Extraction Procedure above for more information.

Phosphate-Phosphorus:

• TNT843 Procedure
• TNT844 Procedure
• TNT845 Procedure

Nitrate-Nitrogen:

• TNT835 Procedure
• TNT836 Procedure

Potassium:

• Potassium Procedure

Total Hardness:

• Total Hardness Procedure

Calcium Hardness:

• Calcium Hardness Procedure

pH:

• pH Procedure

Conductivity:

• Conductivity Procedure