Solid Phase Phosphorus Buffer (Alumina-P)

A major challenge in studies of Phosphorus nutrition is maintenance of realistically low P concentrations under controlled conditions. In 1982, Coltman et al. proposed the use of P-loaded alumina (Al2O3 ) as a phosphorus buffer in the sand culture system. This technique was shown to simulate plant responses to P at concentrations and under conditions comparable to those found in soil and has been used in several laboratories to study plant responses under P stress (Jinming et al., 2005) and to screen for P efficient crops (Pereira and Bliss., 1987; Lynch et al., 1990). In our lab, Alumina-P has been developed and used as a phosphorus buffer in both sand culture and hydroponic system. We also investigate the utility of the Alumina-P as a phosphorus fertilizer for vegetable production (Tanaka et al., 2006). Currently, we are developing Al-P to be used in gel media to facilitate molecular and physiological studies of a model plant, Arabidopsis .

Alumina Loading Procedure for Phosphorus (Modified by Bob Snyder)

Note: This procedure applies to a 20 kg mass of Compalox (AN/V-801; from Albemarle/Martenswerk in Germany) in loading solution volume 70L accomplished in a 55 gallon (208L) stainless steel drum.

Step 1: Wetting Alumina:

  1. Place 20 Kg of raw Compalox alumina in the drum.
  2. Add 70L of distilled water and mix well for 30 seconds with a canoe paddle.
  3. Mix by rotating the drum for 30 minutes to thoroughly wet the alumina.

Step 2: Acidification

  1. Remove 7 L of wetting rinse and discard.
  2. Add 7 L of 2.50 N HCl and mix well by stirring alumina and water with canoe paddle.
  3. Mix by rotation for 1 hr (pH after acidification should be between 3.0-3.5)
  4. Discard the used acid solution.

Step 3: Acid removal rinse 1

  1. Add 70 liters of distilled water to the acidified alumina and stir to mix.
  2. Rotate drum for 30 minutes. (After 30 minutes, the pH should be 3.5-3.7)
  3. Discard the rinse.

Step 4: Acid removal rinse 2

  1. Add 70 liters of distilled water to the acidified alumina and stir to mix.
  2. Rotate drum for 30 minutes. (After 30 minutes, the pH should be 3.8-4.0)

Step 5: Acid removal rinse 3

  1. Add 70 liters of distilled water to the acidified alumina and stir to mix.
  2. Rotate drum for 30 minutes. (After 30 minutes, the pH should be 3.8-4.0)
  3. Retain the rinse for the loading step.

Step 6: Loading the Phosphorus (this example is for loading with 148 mM KH2PO4 )

  1. Remove and discard 10.36L of the last rinse.
  2. Add 10.36L of 1M KH2PO4 and stir with canoe paddle for 1 minute to mix
  3. Rotate the drum for 2 hr to load the KH2PO4 on to alumina matrix.
  4. After loading, remove 2-40 ml samples of the supernatant for P-analysis and pH determination (pH should be 6.5)
  5. Discard the spent loading solution.

Step 7: Final rinse for removal of excess salt

  1. Add 70 L of distilled water to the P-loaded alumina.
  2. Rotate the drum for 30 minutes.
  3. Retain a 40 ml sample of the rinse solution after mixing for P analysis and determination of pH (pH should be 6.5)
  4. Discard the rinse.

Step 8: Drying

  1. Place the loaded alumina on plastic Rubbermaid-type trays, and dry in a 60°C oven.

Step 9: Phosphorus desorption test

  1. Place 0.2 g of dried alumina in 20 ml of distilled water (if using 1% wt/vol in your experiment)
    ** For hydroponic system, do the desorption test in P-free nutrient solution
  2. Allow to stand on the lab bench overnight
  3. Filter the supernatant through a 0.45 um nylon membrane and analyze for phosphorus.

Step 10: Phosphorus analysis

We use a colorimetric method for ortho-phosphate by J. Murphy and J.P Riley, in Anal. Chim. Acta, 27 (1962) 31-36.

** Al-P for gel media is being tested.

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