This method is equivalent to Method 9J1 except that an automated finish (Warrell and Moody 1984) based on the colorimetric procedure of Murphy and Riley (1962) is used to obtain the concentration of P remaining in solution following equilibration with soil. While AutoAnalyzer I/II technology is described, microbore or FIA are appropriate alternatives, ideally without any heating beyond 37°C to speed colour development. The analyst must be guided by the operational instructions and directions given by the manufacturer. This could require changes to the specified reagents and to the flow diagram provided for this method. Whichever technology is used, the results obtained should be close to those obtained by Method 9J1.
0.01 M Calcium Chloride
As for Method 4B1.
Ammonium Molybdate Solution
As for Method 9B2.
Ascorbic Acid Solution
As for Method 9F2.
Potassium Antimony Tartrate Solution
As for Method 9B2.
Working Reagent
As for Method 9F2.
Acid-Phosphate Diluent
As for Method 9F2.
Phosphorus Stock Solution
As for Method 9J1.
Phosphorus Equilibrating Solutions
As for Method 9J1.
Phosphorus Primary Standard
As for Method 9A2.
As for Method 9J1.
Phosphorus Working Standards
As for Method 9J1.
Prepare particulate-free, equilibrated soil extracts as described in Method 9I1 and transfer to dry tubes for automated colorimetric analysis.
Ensure individual components of the continuous flow analyser system for the determination of P are connected as detailed on the segmented flow manifold for calcium chloride-extractable P (Figure 9.10), except that 0.01 M CaCl2 should replace 0.005 M CaCl2 as the sampler wash solution; instrument selections and settings should be in accord with manufacturer’s instructions. This may require changes to the specified reagents and to the flow diagram provided for this method.
‘Condition’ the manifold before use with reagents and relevant standard solutions.
Prepare a calibration curve from the P Working Standards and record the equilibrium P concentration ‘C’ as μg P/L. Also record the supernatant P value as mg P/kg for determination of P sorbed.
As for Method 9J1.
Report EPC and PBC on an air-dry basis.