AOAC RI ERP EBOOK FOR FERTILIZERS

AOAC RESEARCH INSTITUTE AOAC OFFICIAL METHODS OF ANALYSIS (OMA)

OMAMAN-28/AOAC 2006.03 Study Director: Sharon Webb, University of Kentucky, Division of Regulatory Services, 103 Regulatory Services Bldg, Lexington , Kentucky 40546-0275

TECHNICAL EVALUATION CRITERIA Is the test kit method scientifically and technically sound? ER 1 Yes ER 2 Yes ER 3

No, The method states it is intended for fertilizers but; 1). Targets some metals and ignores others (e.g. Al, Hg) that can be toxic to plants 2). Has a bias toward metals extractable by acid whereas alkali extraction is ignored. It is known that some metals are more available in alkali environments. 3). If a method is to be used for determining metals in fertilizers it should consider the pH range of soils wherein most crops are grown (pH 5.5-6.5) and, although environmental tests for metals may include highly acidic soils, this is not the case for agricultural soils where pH ranges are normally maintained within a specific range and may likely include alkali soils above pH 8.0. in areas of low rainfall or where irrigation waters contain high salts 4). If the purpose is to limit plant availability then a leachable metals test would be more appropriate than a total metals test considering that metals must be released from the fertilizer into soil solution in order for plant uptake to occur and only certain forms of some metals are plant available 5). To include plant macro- and micronutrients such as Ca, Mg, Fe, etc. in this method for total metals could be deceptive resulting in label guarantees for these fertilizer nutrients. This total metals would not be indicative of plant availability and would be doing a great disservice to the end user. This has already happened in some states where a label warning is being construed as a nutrient guarantee. 6.) As there are numerous methods for metals analysis if we are going to advance a method it should therefore have some value or indication of its solubility from the fertilizer material and potential plant availability (solubility in soil solution and leachability). This is not what this method is meant to determine (its scientific purpose).

ER 4 ER 5 ER 6 ER 7 ER 8 ER 9

Yes Yes Yes Yes Yes Yes

ER 10 Yes Have sufficient controls been used, including those required to calculate the rate of false‐positive and false‐negative results where appropriate? ER 1 No, The carbon interference/background for wavelengths below 250nm is not sufficiently addressed. ER 2 Yes ER 3 No, Should have both alkali and acidic measurements Should list pH of extractants. May have complexation with other elements during wait time Page 1 of 14