This method is identical to Method 7D2a, except that it uses an FIA finish rather than an automated colour, continuous segmented flow finish.
FIA Instrumentation (see Figure 7.12)
See Methods 7A2b, 7B1b, 7C2b and 7D1b and as guided by the system’s manufacturer.
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
As for Method 7C2b – NH4-N only.
PMN (Ammonium) Standard Solutions
As for Method 7D1a.
Guided by Method 7D2a, sieve field-moist samples, determine moisture content, then weigh two by 5.0 g oven-dry equivalent soil samples. Transfer one of these into a 100 mL Extracting Bottle/Flask for ‘immediate extraction’ and the second into a universal bottle for ‘seven-day incubation’ then proceed as for Method 7D2a. The effective soil/solution ratio is 1:10.
Proceed using results from both the ‘immediate’ extraction sample extracts and the ‘incubated’ (Day 7) sample extracts, as described in Method 7D2a.
Report PMNAn-N (mgN/kg) to the nearest whole number on an oven-dry basis.
Figure 7.12. FIA manifold for ammonium-N in 2 M KCI extracts.