Soluble Phosphorus

Reagents

  1. Deionized water
  2. ICP standard for phosphorus

Apparatus

  1. Shaker
  2. 250 mL Erlenmeyer Flasks with stoppers
  3. Balance
  4. Whatman No. 40 filter paper and filter funnels
  5. Disposable pipets
  6. ICP test tubes

Procedure

  1. Determine dry matter of sample.
  2. Weigh amount of fresh sample necessary to come up with the equivalent of 1.0 grams dry sample (use computer program to determine weight to use).  Weigh into tared 250 mL Erlenmeyer flask.  (Do samples in duplicate).
  3. Bring weight to 100 g with water.  Note:  For liquid samples if dry matter < 0.5 %, the liquid can be filtered directly without adding more water.
  4. Stopper and shake for 60 minutes.
  5. Filter sample through No. 40 Whatman or equivalent filter paper into an ICP test tube.
  6. Analyze filtrate for P on the ICP.  Analyze samples same day as preparation.

Calculations

  1. The ICP values will be on a dry weight basis.  Exception:  If DM < 0.5% and, therefore, if liquid sample is filtered directly, there is no dilution factor, therefore, the direct reading from the ICP is ppm on an as-samples "A" basis, so the ICP reading should be final value on report.  To get that value, take (ICP reading) / ((100)(dry matter)).  For example, if ICP value = 30 and DM = 0.23, report 30 /((100)(0.23)) = 1.3043.
  2. For other samples, dilution is 1 to 100 (1.0 g dry weight to 100 g).  Record with 2 decimals for liquids and 0 decimals for solids.  Examples:  If ICP value = 42.33 record 42 for solids and 42.33 for liquids.

Reference

  1. Sharpley, Andrew and Barton Moyer, 2000.  Phosphorus Forms in Manure and Compost and Their Release during Simulated Rainfall.  J. Environ.  Qual.  29:1462 - 1469.