AOAC ERP Fertilizers - December 2017

M. Expression of Results Results for each extraction are presented as a cumulative percentage of total nutrient. Extraction 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 1 and expressed according to their definition. N. Calculations and Graphing the Release Plot ( a )  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 (in mg/L) of nutrient/analyte in Extract 1, where A can be N, P, or K. %AR (ex1) = % Nutrient released during Extraction 1, where A can be N, P, or K. AC (ex2) = Concentration (in mg/L) of nutrient in Extract 2, where A can be N, P, or K. %AR (ex2) = % Nutrient released during Extraction 2, where A can be N, P, or K. AC (ex3) = Concentration (in mg/L) of nutrient in Extraction 3, where A can be N, P, or K. %AR (ex3) = % Nutrient released during Extraction 3, where A can be N, P, or K. AC (ex4) = Concentration (in mg/L) of nutrient in Extraction 4, where A can be N, P, or K. %AR (ex4) = % Nutrient released in Extraction 4, where A can be N, P, or K. A (tr) = % Total release of all extractions, where A can be N, P, or K. A (ne) = % Controlled release (nutrient not extracted, calculated below), where A can be N, P, or K. A (cr) =%Controlled release (nutrient released in Extractions 2–4), where A can be N, P, or K. W = Total unground test portion weight in g. %TAR = Total nutrient (analyte) released, where A can be N, P, or K. WIN = Water-insoluble N. 1.02 = Dilution factor (due to addition of the preservative) = 255 mL/250 mL. V = Total volume of respective extract in L. ( b )  Calculations. — Note : An example calculation can be found in Appendix B of ref. 2 available on the J. AOAC Int . website.

mg L

1 g 1000 mg

0.255 L 0.250 L

×

×

×

( ) AC , ex1

V, L

×

( ) ex1

%AR =

100

g 100 g

×

() t

W, g A ,

mg L

1 g 1000 mg

0.255 L 0.250 L

×

×

×

( ) AC , ex2

V, L

×

( ) ex2

%AR =

100

g 100 g

×

() t

W, g A ,

mg L

( ) AC , ex2

mg L

1 g 1000 mg

0.255 L 0.250 L

−

×

×

×

( ) AC , ex3

V, L

2

×

( ) ex3

%AR =

100

g 100 g

×

() t

W, g A ,

mg L

( ) AC , ex3

mg L

1 g 1000 mg

0.255 L 0.250 L

−

×

×

×

( ) AC , ex4

V, L

2

×

( ) ex4

%AR =

100

g 100 g

×

() t

W, g A ,

=

+

+

+

( ) ex1

( ) ex2

( ) ex3

( ) ex4

%TAR %AR

%AR

%AR

%AR

( ) ( ) = − () () %WIN A % A % t t

%AR

( ) ex1

100

( c )  Graphing the release plot. —Plot the cumulative % of analyte (nutrient) released on the y -axis versus the time in hours of extraction on the x -axis. The release plot will be similar to Figure 2015.15B , except for a change in the units on the x -axis from cumulative days of extraction to cumulative hours of extraction. An example graph can be found in Appendix B of ref. 2 available on the J. AOAC Int . website. References: (1) Medina, L.C., Sartain, J.B., Obreza, T.A, Hall,

W.L., & Thiex, N.J. (2014) J. AOAC Int. 97 , 643– 660. http://dx.doi.org/10.5740/jaoacint.13-065 (2) Medina, L.C., Sartain, J.B., Obreza, T.A, Hall, W.L., & Thiex, N.J. (2014) J. AOAC Int. 97 , 661– 676. http://dx.doi.org/10.5740/jaoacint.12-482 J. AOAC Int . 99 , 353(2016) DOI: 10.5740/jaoacint.15-0294

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