REAGENTS

  1. Azomethine - H
  2. Ascorbic Acid
  3. Ammonium Acetate
  4. EDTA tetrasodium salt
  5. Nitrilotriacetic acid disodium salt
  6. Sodium acetate
  7. Acetic acid
  8. 1000 ppm B - certified, NIST traceable standard
  9. Activated charcoal

STANDARDS

  1. Stock Solution:
    1. 10 ppm B - pipet 10 mL of 1000 ppm B into a 1 liter volumetric flask. Dilute to volume with deionized water and mix well. Store in plastic bottles.
    2. Instrument Calibration Standards - pipet the designated mL of 10 ppm B stock solution into 100 mL volumetric flasks. Dilute to volume with deionized water and mix well. Store in plastic bottles.
Standard # Stock Solution
mL 		Final Concentration
ppm
10.101.00
20.202.00
30.303.00
40.404.00
50.505.00

AZOMETHINE-H SOLUTION

  1. Weigh 0.90 g azomethine-H into a 100 mL volumetric flask containing 50 mL deionized water.
  2. Add 2 g ascorbic acid.
  3. Dissolve by heating gently in a hot water bath and let cool.
  4. Dilute to volume with deionized water and mix well. If solution is turbid, heat again in the hot water bath, making up to original volume after cooling. Store in a refrigerator for up to 48 hours.

BUFFER-MASKING AGENT

  1. Weigh 250 g ammonium acetate into a 1 liter beaker containing 400 mL deionized water.
  2. Add 25 g EDTA tetrasodium salt
  3. Add 10 g nitrilotriacetic acid disodium salt.
  4. Dissolve and then add slowly 125 mL acetic acid and mix well.

MORGAN'S EXTRACTION SOLUTION

  1. Weigh 100 g sodium acetate into a 1 liter beaker containing 800 mL deionized water. Dissolve and mix well.
  2. Adjust pH to 4.8 with acetic acid.
  3. Transfer to a 1 liter volumetric flask. Dilute to volume with deionized water and mix well.

EXTRACTION PROCEDURE

  1. Scoop 5 g soil into a 40 mL extraction bottle.
  2. Add 1/4 teaspoon activated charcoal.
  3. Add 25 mL. Morgan's Extract.
  4. Shake for 5 minutes on a shaker box at high speed (250 oscillations per min). 5. Filter using Whatman #42 paper.
  5. Prepare an extraction blank consisting of 1/4 teaspoon charcoal and 25 mL. Morgan's Extract.

COLOR DEVELOPMENT PROCEDURE

  1. Pipet 3 mL of soil extract into a polystyrene test tube.
  2. Add 1 mL of Buffer-Masking agent and mix well.
  3. Add 1 mL of azomethine-H solution and mix well.
  4. Let stand for 1 hour.
  5. Read on a colorimeter or spectrophotometer set at 430 nm.

CALCULATION

[ppm boron(sample) - ppm boron(blank)] X 10 = lbs boron/acre

REFERENCES

  1. Basson, W. D., R. G. Bohmer, and D. A. Stanton. 1969. An automated procedure for the determination of boron in plant tissue. Analyst 94:1135-1141
  2. Wolf, B. 1971. The determination of boron in soil extracts, plant materials, compost, manure, water, and nutrient solutions. Commu. Soil Sci. Plant Anal. 2:363-374.
  3. Wolf, B. 1974. Improvements in the azomethine-H method for the determination of boron. Commu. Soil Sci. Plant Anal. 5(1):39-44.