Method F-013A The Determination of Exchangeable Sodium in soils

Equipment Required:

1. Sherwood Flame Photometer
2. Balance weighing to +-0.0005g
3. Centrifuge
4. Sodium chloride (analar)
5. 1 molar ammonium acetate solution

Method:

1. To 10g soil add 200ml of 1 molar neutral ammonium acetate solution. Allow to stand for 18 hours stirring occasionally.
2. Withdraw and centrifuge the suspension.
3. Transfer 5ml of the supernatant liquid to a 50ml volumetric flask and dilute to the mark.
4. . Prepare a 5mg/l sodium standard in 1 molar neutral ammonium acetate solution.
5. Prepare from the above 2.5mg/l and 1.25mg/l Na standards in 1 molar ammonium acetate solution.
6. Aspirate the 5mg/l standard into the Sherwood Flame Photometer and adjust the display to a suitable reading.
7. Aspirate the other standards and plot a standard curve of meter reading vs concentration.
8. Aspirate the sample and record its meter reading.
9. Read off the concentration of the sample from the standard curve.
10. Multiply the mg/l sodium value by 2 to give mg sodium per 1Og soil.