7D1b Potentially mineralisable N, hot-KCl extraction (PMN_KCl) – automated colour, FIA

This method is identical to Method 7D1a, except that it uses an FIA finish rather than an automated colour, continuous segmented flow finish.

Apparatus

FIA Instrumentation

See Methods 7A2b, 7B1b and 7C2b, and as guided by the system’s manufacturer.

Reagents

2 M KCl Extracting Solution

As for Method 7C1. Ensure any stored solution is well stoppered to prevent NH₃ absorption from the laboratory environment.

Other Reagents

Prepare as for Method 7C2b – NH₄-N only.

PMN_KCl (Ammonium) Standard Solutions

Prepare as for Method 7D1a.

Procedure

Soil extraction and preparation of extracts for analysis, commencing with 3.0 g air-dry soil (<2 mm) is exactly as for Method 7D1a. Next analyse the clarified extracts by FIA, guided by Method 7C2b, except that the effective soil/extract ratio is 1:16.67 rather than 1:10.

Calculation and Reporting of PMN_KCl

Net PMN_KCl = Measured PMN_KCl – Mineral N from Method 7C2a/b (or equivalent), with all expressed as mg N/kg, air-dry.