AOAC ERP Fertilizers - December 2017

T hiex : J ournal of AOAC I nternational V ol . 99, N o . 2, 2016  359

Calculations. — Note : An example calculation can be found in Appendix B of ref. 2 available on the J. AOAC Intl . Web site.

Discussion

Medina et al.’s validated methods, including alternatives for a 180 day extraction and an accelerated extraction (1, 2), were submitted by William Hall to the AOAC Fertilizer Expert Review Panel (ERP), and adopted as First Action. Extensive method development and validation data supporting both alternatives as documented in Medina et al.’s studies (1, 2, 6) was further reviewed by the ERP. The validation was deemed thorough by the ERP, demonstrated that the method was scientifically sound, and confirmed that such a method is needed by the community. Method reproducibility for both alternatives is proposed to be determined via collaborative study. The ERP asked that in addition to solid fertilizers, reproducibility data for liquid fertilizers be generated. The ERP also asked that the 180 day ambient method be clarified for its application to coated fertilizers (not including sulfur-coated) as reproducibility data are generated. It was noted that it might be difficult to obtain reproducibility data on the 180 day extraction within 2 years due to the long analysis time. The collaborative studies will provide reproducibility data for N, P, K, and possibly other nutrients. (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 (3) Association of American Plant Food Control Officials, Inc. (1995) AAPFCO Official Publication No. 48 , D.L. Terry (Ed.), West Lafayette, Indiana. (4) Thiex, N. (2014) J. AOAC Int. 97 , 641–642. http://dx.doi. org/10.5740/jaoacint.SGEThiex_Intro (5) Sartain, J.B., Hall, W.L., Littell, R.C., & Hopwood, E.W. (2004) in Environmental Impact of Fertilizer on Soil and Water , W.L. Hall & W.P. Robarge (Eds), Oxford University Press, Washington, DC, pp 180–195 (6) Medina, L.C., Sartain, J.B, Obreza, T.A, Hall, W.L., & Thiex, N.J. (2014) J. AOAC Int. 97 , 677–686. http://dx.doi. org/10.5740/jaoacint.13-004 References

      

      

  ×

 

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 ,

  +  

  +  

  +  

 

= 

%TAR %AR

%AR

%AR

%AR

( ) ex1

( ) ex2

( ) ex3

( ) ex4



   

   

( ) ( ) = −  ( ) ( ) %WIN A % A % t t

   

%AR

( ) ex1

  

100

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 . web site.

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