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Phosphorus Sorption

By Jared L. DeForest [link to his bio]

Reagents

In a 10 liter carboy

  • 7.46 g Potassium Chloride (0.01 M KCl)
  • Bring to volume with DI water.

Stock solution (1000 µg P/ml) (H4)

In 1 liter volumetric flask

  • 4.39 g Oven-dried KH 2 PO 4
  • Bring to volume with DI water.

Store in bottle at 4°C with 2 drops of chloroform.

Follow the adjacent table for P working solution (enough for 32 samples).

Dilute daily from stock solution.

µg P/mlppm

    (ppm)   

Stock(ml)

(ml)  

0.01 M KCl(ml)

(ml)        

0

0

1000

10

10

990

25

25

975

50

50

950

100

100

900

150

150

850

200

200

800

Procedure

In a 50 ml Oakridge centrifuge tube

  • 3 g Oven-dried equivalent sieved soil (field fresh)
  • 30 ml P working standards at each concentration
  • 1 drop Chloroform

Shake for 2 days at 150 rpm and then centrifuge for 1 hour.

Repeat the procedure, but add 2 bicarb charged resin strips.

Analyze solutions for ortho-P using the ascorbic acid method.

Calculations

Xs = [(s – c) × F] - E

Where:

  • Xs = sorbed P at working solution concentrations (µg P/g soil)
  • s = µg P/ml of original working solution
  • c = µg P/ml of working solution after shaking (i.e., equilibrium)
  • F = ml working solution/g dry soil (e.g. 10 ml/g = 30 ml/3 g dry soil)
  • E = resin-extractable P (µg P/g soil)

Adapted from Tiessen et al (1991) Geoderma and Lajtha K. et al. (1999) Soil Phosphorus. Standard soil methods for long-term ecological research .

Created: 08/19/09

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