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precipitation in columns or tubing, flush by circulating 2% HCl through system for 5 min.
Follow with two 5 min DI water washes. If there is no buildup, water washes are sufficient. Allow
columns to dry before placing new packing and samples in column for next run.
G. Analytical Determinations
Determine nutrients of interest (e.g., N, P, and K) on each of the extracts obtained.
(a) Determine total N using AOAC Method
993.13
(combustion) or AOAC Method
978.02
(modified comprehensive) or other equivalent, applicable methods validated in your laboratory.
Utilize applicable method-matched reference material in each run. Utilize internal reference
standard appropriate for the range of the sample extracts; typically 100, 1000, and 10000 mg
N/L will cover the full range of N concentrations.
(
b
) Determine total phosphate (as P2 O 5 ) using AOAC Method
962.02
or AOAC Method
978.01
(1)
or equivalent, applicable methods validated in your laboratory. Utilize applicable method-
matched reference material in each run. Utilize internal reference standard appropriate for the
range of the sample extracts; typically 100, 1000, and 10000 mg P 2 O5 /L will cover the full range
of P 2 O5 concentrations.
(
c
) Determine soluble potash (as K 2 O) using AOAC Method
958.02
(STPB) or AOAC Method
983.02
(flame photometry; 1) or equivalent, applicable methods validated in your laboratory.
Utilize applicablemethod-matched referencematerial in each run of samples. Utilize internal
reference standard appropriate for the
range of the sample extracts; typically 100, 1000, and 10
000 mg
.
K2 O/L will cover the full range of K2 O concentrations.
H. Expression of Results
Results for each extraction are presented as a cumulative percentage of total nutrient. Extraction
No. 1 is water-soluble and not a slow-release fraction. However, slowly available water- soluble
materials (low MW urea formaldehydes and methylene ureas) may be present. These materials
can be analyzed directly from extraction No. 1 and expressed according to their definition.
I. Calculations and Graphing the Release Plot
Nomenclature for Extraction Calculations
A (t) = % Total nutrient/analyte determined as in the
Analytical Determinations
section above
where A can be N, P, or K.
AC (ex1) = Concentration (inmg/L) of nutrient/analyte in extract No. 1, where A can be N, P, or K.
%AR (ex1) = % Nutrient Released during extraction No. 1, where A can be N, P, or K.
Candidates for 2016 Method of the Year
214