AOAC ERP Fertilizers - March 2019

3/14/2019

AOAC EXPERT REVIEW PANEL FOR FERTILIZERS

UPDATE ON ADDITIONAL VALIDATIONS AND NEXT STEPS FOR THE METHOD  • Validation Materials/Test Samples • Selection – Several materials have been selected and are ready for preparation and reduction to be sent out to  collaborators. • Homogeneity testing – Has not yet been done because the final number and makeup of the unknown samples has  not been finalized • A key aspect of this procedure is that because the slow and controlled release properties of the materials is due  either to a coating over a soluble substrate, or to the relative slow dissolution of nutrients due to their solubility.  Thus any grinding or size reduction is not an option to reduce variability. Consequently, a large test portion (~30 g)  must be selected with great attention to the method of sample reduction to achieve a representative test portion.   • Method “updates” • The only modification that has been introduced is the option to reduce the test portion weight to ~6 g for single  compound slow release materials where sample/solvent ratio is a limiting factor in the extraction process. • There is great interest in testing other nutrients beyond nitrogen for SRF/CRF properties. Since the extracts can be  stabilized and saved, the testing of additional nutrients will be encouraged, but not required by collaborators. 

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AOAC EXPERT REVIEW PANEL FOR FERTILIZERS

UPDATE ON ADDITIONAL VALIDATIONS AND NEXT STEPS FOR THE METHOD  • Why isn’t this done????

• The study director was given other higher priority assignments. Now that the study director no longer is  employed by the previous employer it is believed that the work can begin again in earnest this year. • What needs to be done to get this moving again? • Finalize list of unknown samples and get it reviewed by appropriate experts e.g. statisticians, to assure that  there are adequate numbers and types of samples to support the scope, matrices, mechanisms and range of  nutrient concentrations that will be useful to the community.  • Finalize the list of labs willing to invest in the equipment and time to participating in the study. The ambient soil  extraction takes 180 days just for the extraction and there will be at lease three replicates required . • Several labs have expressed interest in running one or both of the extraction alternatives, a list of labs that  will commit to participating needs to be finalized. But until the number of samples and timeframe for  sample distribution and testing are set, the final number of labs can not be verified.  • Timeframe for completion of the study – • Due to the extraordinary time for completing the ambient extraction, it will very likely be a year or more before  the study is completed once it begins. However a lab need not wait until the ambient extractions are complete  (180 days) to start its duplicate analysis. It should wait at least a month before starting its duplicate analysis to  assure that the conditions in the lab are sufficiently different to assume it is indeed a blind duplicate.

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