Phosphorus Sorption
By Jared L. DeForest
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 KH2PO4
- 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/ml ppm | Stock (ml) | 0.01 M KCl (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