Symposium review: Fiber and in vitro methods, analytical variation, and contributions to feed analysis.

At least 2 basic inputs are needed to formulate rations: the nutritional requirements of the animals to be fed and the nutritional composition of the feeds. David R. Mertens not only defined fiber requirements for dairy cattle but became a leading expert in the laboratory measurement of fiber in feeds, digesta, and feces. Fiber is a heterogeneous nutritional entity composed mainly of polysaccharides and polyphenolics. Because the method defines the fiber that is measured, methods must be described thoroughly and followed exactly to obtain results that are repeatable within a laboratory and reproducible among others. Filtration of neutral detergent fiber (NDF) can be difficult, and those who have worked in his laboratory can attest that Mertens rigorously studied this, along with other method details to improve NDF analysis from sample preparation to blank corrections. Mertens's procedure for amylase-treated NDF (aNDF), using α-amylase and sodium sulfite with crucibles, culminated in the Association of Official Analytical Chemists Official Method 2002.04 for aNDF, which was also accepted as International Standard ISO 16472:2006 and is used worldwide as a reference method for feed evaluation. Because aNDF digestibility is variable and a key factor in overall digestibility, Mertens also worked to improve in vitro ruminal digestibility and gas production procedures within and among laboratories, including procedures using flasks or filter bags. His in vitro gas production method is currently used by commercial laboratories that generate a significant share of the aNDF digestibility results reported worldwide. Outside of the laboratory, his extensive outreach to commercial and research laboratories has had a huge impact on fiber analysis, in vitro digestibility, and other laboratory procedures. While advising the National Forage Testing Association, Mertens provided program infrastructure that improved laboratory proficiency in more than 120 laboratories in the United States and around the world. Most importantly, thanks to his advances in fiber analysis and in vitro digestibility techniques, Mertens has enhanced the evaluation of feeds and the nutrition and health of dairy cows. These contributions have helped thousands of dairy farmers and nutritionists around the globe and continue to have a substantial impact on the industry.

Towards a unified sampling terminology: clarifying misperceptions.

International acceptance of data is a much-desired wish in many sectors to ensure equal standards for valid information and data exchange, facilitate trade, support food safety regulation, and promote reliable communication among all parties involved. However, this cannot be accomplished without a harmonized approach to sampling and a joint approach to assess the practical sampling protocols used. Harmonization based on a nonrepresentative protocol, or on a restricted terminology tradition forced upon other sectors would negate any constructive outcome. An international discussion on a harmonized approach to sampling is severely hampered by a plethora of divergent sampling definitions and terms. Different meanings for the same term are frequently used by the different sectors, and even within one specific sector. In other cases, different terms are used for the same concept. Before efforts to harmonize can be attempted, it is essential that all stakeholders can at least communicate effectively in this context. Therefore, a clear understanding of the main vocabularies becomes an essential prerequisite. As a first step, commonalities and dichotomies in terminology are here brought to attention by providing a comparative summary of the. terminology as defined by the Theory of Sampling {TOS) and those in current use by the International Organization for Standardization, the World Health Organization, the Food and Agriculture Organization Codex Alimentarius, and the U.S. Food and Drug Administration. Terms having contradictory meaning to the TOS are emphasized. To the degree possible, we present a successful resolution of some of the most important issues outlined, sufficient to support the objectives of the present Special Section.

Evaluation of a soil incubation method to characterize nitrogen release patterns of slow- and controlled-release fertilizers.

Several technologies have been proposed to characterize the nutrient release patterns of slow-release fertilizers (SRF) and controlled-release fertilizers (CRF) during the last few decades. These technologies have been developed mainly by manufacturers, and are product-specific, based on the regulation and analysis of each SRF and CRF product. Despite previous efforts to characterize SRF and CRF materials, no standardized, validated method exists to assess their nutrient release patterns. However, the increased production and distribution of these materials in specialty and nonspecialty markets requires an appropriate method to verify product claims and material performance. A soil incubation column leaching procedure was evaluated to determine its suitability as a standard method to estimate nitrogen (N) release patterns of SRFs and CRFs during 180 days. The influence of three soil/sand ratios, three incubation temperatures, and four soils on method behavior was assessed using five SRFs and three CRFs. In general, the highest soil/sand ratio increased the N release rate of all materials, but this effect was more marked for the SRFs. Temperature had the greatest influence on N release rates. For CRFs, the initial N release rates and the percentage N released/day increased as temperature increased. For SRFs, raising the temperature from 25 to 35 degreesC increased initial N release rate and the total cumulative N released, and almost doubled the percentage released/day. The percentage N released/day from all products generally increased as the texture of the soil changed from sandy to loamy (lowa>California>Pennsylvania>Florida). The soil incubation technique was demonstrated to be robust and reliable for characterizing N release patterns from SRFs and CRFs. The method was reproducible, and variations in soil/sand ratio, temperature, and soil had little effect on the results.

Optimization and validation of an accelerated laboratory extraction method to estimate nitrogen release patterns of slow- and controlled-release fertilizers.

Several technologies have been proposed to characterize the nutrient release and availability patterns of enhanced-efficiency fertilizers (EEFs), especially slow-release fertilizers (SRFs) and controlled-release fertilizers (CRFs) during the last few decades. These technologies have been developed mainly by manufacturers and are product-specific based on the regulation and analysis of each EEF product. Despite previous efforts to characterize EEF materials, no validated method exists to assess their nutrient release patterns. However, the increased use of EEFs in specialty and nonspecialty markets requires an appropriate method to verify nutrient claims and material performance. A series of experiments were conducted to evaluate the effect of temperature, fertilizer test portion size, and extraction time on the performance of a 74 h accelerated laboratory extraction method to measure SRF and CRF nutrient release profiles. Temperature was the only factor that influenced nutrient release rate, with a highly marked effect for phosphorus and to a lesser extent for nitrogen (N) and potassium. Based on the results, the optimal extraction temperature set was: Extraction No. 1-2:00 h at 25 degrees C; Extraction No. 2-2:00 h at 50 degrees C; Extraction No. 3-20:00 h at 55 degrees C; and Extraction No. 4-50:00 h at 60 degrees C. Ruggedness of the method was tested by evaluating the effect of small changes in seven selected factors on method behavior using a fractional multifactorial design. Overall, the method showed ruggedness for measuring N release rates of coated CRFs.

Statistical correlation of the soil incubation and the accelerated laboratory extraction methods to estimate nitrogen release rates of slow- and controlled-release fertilizers.

Several technologies have been proposed to characterize the nutrient release patterns of enhanced-efficiency fertilizers (EEFs) during the last few decades. These technologies have been developed mainly by manufacturers and are product-specific based on the regulation and analysis of each EEF product. Despite previous efforts to characterize nutrient release of slow-release fertilizer (SRF) and controlled-release fertilizer (CRF) materials, no official method exists to assess their nutrient release patterns. However, the increased production and distribution of EEFs in specialty and nonspecialty markets requires an appropriate method to verify nutrient claims and material performance. Nonlinear regression was used to establish a correlation between the data generated from a 180-day soil incubation-column leaching procedure and 74 h accelerated lab extraction method, and to develop a model that can predict the 180-day nitrogen (N) release curve for a specific SRF and CRF product based on the data from the accelerated laboratory extraction method. Based on the R2 > 0.90 obtained for most materials, results indicated that the data generated from the 74 h accelerated lab extraction method could be used to predict N release from the selected materials during 180 days, including those fertilizers that require biological activity for N release.

Simultaneous determination of arsenic, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, selenium, and zinc in fertilizers by microwave acid digestion and inductively coupled plasma-optical emission spectrometry detection: single-laboratory validation of a modification and extension of AOAC 2006.03.

A single-laboratory validation study was conducted for the simultaneous determination of arsenic, cadmium, calcium, cobalt, copper, chromium, iron, lead, magnesium, manganese, molybdenum, nickel, selenium, and zinc in all major types of commercial fertilizer products by microwave digestion and inductively coupled plasma-optical emission spectroscopy analysis. This validation study proposes an extension and modification of AOAC 2006.03. The extension is the inclusion of calcium, copper, iron, magnesium, manganese, and zinc, and the modification is incorporation of hydrochloric acid in the digestion system. This dual acid digestion utilizes both hydrochloric and nitric acids in a 3 to 9 mL volume ratio/100 mL. In addition to 15 of the 30 original validation materials used in the 2006.03 collaborative study, National Institute of Standards and Technology Standard Reference Material 695 and Magruder 2009-06 were incorporated as accuracy materials. The main benefits of this proposed method are a significant increase in laboratory efficiency when compared to the use of both AOAC Methods 965.09 and 2006.03 to achieve the same objective and an enhanced recovery of several metals.

Piloting a Proficiency Testing Program for Laboratory Sampling of Animal Feed Materials.

BACKGROUND: Laboratory sampling is a significant source of error in feed testing. Proficiency testing programs such as the Association of American Feed Control Officials Proficiency Testing Program are an effective means of assessing error in and among analytical methods. However, all proficiency test items are comminuted and blended to control variability among items, effectively minimizing sampling error. Currently there is no mechanism for monitoring sampling error among laboratories. OBJECTIVE: The objective of this work was to investigate the feasibility of a proficiency testing program for laboratory sampling methods and provide insight into a program to advance the performance of sampling in laboratories. METHODS: The study involved the fabrication of identical feed test items from feed ingredients and shipping the uncomminuted materials to volunteer laboratories. The volunteer laboratories followed in-house procedures for selecting test portions for routine feed tests. Tests on all the test portions for a single analyte were performed by a single laboratory, so that the variability in test results could be attributed to laboratory sampling processes to select test portions. RESULTS: The average RSD, %, for Item A and Item B, respectively, were as follows: protein, 5.08 and 5.23; non-protein nitrogen, 8.90 and 16.6; crude fat, 3.45 and 5.67; vitamin A, 33.9 and 26.9; calcium, 21.9 and 23.6; zinc, 17.9 and 27.9; and copper, 17.4 and 27.9. CONCLUSION: This study suggests that a proficiency testing program for laboratory sampling is feasible with manual manufacture of the test items, and data can be used to monitor laboratory sampling proficiency and also to compare the performance of different laboratory sampling methods. HIGHLIGHTS: The data illustrates that each analyte has unique distributional and compositional heterogeneity, thus unique sampling error, even when multiple analytes are determined from a single test portion.

Determination of direct available phosphate in fertilizers by a discrete analyzer: single-laboratory validation.

To improve throughput during peak seasonal demand, a screening method for the determination of fertilizer-available phosphate using a discrete analyzer for semi-automation was validated in a single laboratory. The fertilizer materials were extracted using a neutral EDTA-ammonium citrate solution as detailed in AOAC Official Method 993.31. Phosphate was subsequently freed from the matrix and converted to orthophosphate using an alkaline persulfate digestion modified from a U.S. Geological Survey water method. Phosphorus was determined colorimetrically on a discrete analyzer. Twelve check samples from the Magruder Fertilizer Check Sample Program and Association of Fertilizer and Phosphate Chemists Fertilizer Check Program were used for method validation experiments. The proposed method is linear from 0.01 to 20 mg/L (ppm) phosphorus. Recovery for all materials averaged 101%, with a range of 99.2 to 103%. Bias for all materials averaged 0.59% with a range of -0.11 to 1.68%, with bias increasing at concentrations of available phosphate exceeding 40%. The LOD was calculated to be 0.001% available phosphate and the LOQ 0.002% available phosphate. The method was found fit for purpose as a screening method for available phosphate analysis in fertilizers.

Determination of ash in animal feed: AOAC official method 942.05 revisited.

AOAC Official Method 942.05, Ash in Animal Feed, has been applied in feed laboratories since its publication in the Official Methods of Analysis in 1942. It is a routine test with renewed interest due to the incorporation of "ash values" into modern equations for the estimation of energy content of dairy feed, beef feed, and pet food. As with other empirical methods, results obtained are a function of the test conditions. For this method, the critical conditions are the ignition time, ignition temperature, and any other furnace or weighing conditions. Complete ignition can be observed by the absence of black color (due to residual carbonaceous material) in the ash residue. To investigate performance of AOAC 942.05, 15 samples were chosen to be representative of a wide range of feed materials. These materials were tested at the conditions of AOAC 942.05 (ignition at 600 degrees C for 2 h) and similar or more rigorous conditions. The additional conditions investigated included: 600 degrees C for 4 h; 600 degrees C for 2 h, cool, and ignite 2 additional h; 600 degrees C for 2 h, cool, wet, dry, and ignite 2 additional h; 550 degrees C for 6 h; 550 degrees C for 3 h, cool, and ignite 3 additional h; and 550 degrees C for 3 h, cool, wet, dry, ignite 3 additional h. Results for all other conditions investigated were found to be significantly different from the current AOAC Method 942.05. All ignition conditions were significantly different from each other except two: 550 degrees C for 3 h, cool, ignite 3 additional h; and 550 degrees C for 3 h, cool, wet, dry, and ignite 3 additional h. Recommendations for modification to AOAC Official Method 942.05 are suggested based on statistical analysis of the data and a review of the literature.

Effect of Test Portion Mass on Vitamin A Testing in Animal Feed Materials.

BACKGROUND: Vitamin A test results have historically been notorious for poor repeatability and reproducibility. This problem has been discussed at length in Association of American Feed Control Officials Laboratory Methods and Services Committee meetings. OBJECTIVE: The objective of this work was to assess the effect of test portion mass on the repeatability of vitamin A test results. METHODS: The study was conducted in two parts. In Part I, fundamental sampling error (FSE) was determined experimentally through replicated (n = 16) vitamin A testing of three animal feed materials. The testing followed rigorous test portion selection for 10 g and 100 g test portions. In Part II, FSE calculations were made (1) using theoretical equations based on vitamin A as a liberated analyte and (2) on representing the particles in feed materials. Particle size characterization of vitamin A ingredients was estimated by microscopy and further evaluated by particle size analysis. RESULTS: RSDs, % for vitamin A determinations ranged from 10.5-24.7, and 2.26-10.7 for 10 g and 100 g test portions, respectively. FSE calculated for Ingredient A ranged from 18.3-101% and 5.79-32.0% for 10 g and 100 g test portions, respectively, and for Ingredient B, ranged from 10.2-56.2% and 3.21-17.8% for 10 g and 100 g test portions, respectively. CONCLUSION: Test portion mass has a substantial impact on FSE and is an important factor in controlling the random error in vitamin A testing. FSE equations are useful to approximate minimum test portion mass. HIGHLIGHTS: Vitamin A method development should use theoretical predictions and experimental verification to guide test portion mass. Strategies to deal with the larger test portion masses will be key to validating new methods.

Hepatic element concentrations of lesser scaup (Aythya affinis) during spring migration in the upper Midwest.

High concentrations of some hepatic elements might be contributing to the decline of the continental lesser scaup (Aythya affinis) population. We evaluated hepatic element concentrations of male and female lesser scaup collected from the upper Midwest (Iowa, Minnesota, North Dakota, and South Dakota) during the 2003 and 2004 spring migrations. We measured concentrations of 24 elements in livers of 117 lesser scaup. We found that only selenium concentrations were at levels (>3.0 µg/g wet weight [ww)]) proposed to adversely affect reproduction. Approximately 49% of females (n = 61) had individual hepatic concentrations >3.0 µg/g ww selenium (Se). Our observed hepatic concentration of Se was similar to that reported in lesser scaup collected from the mid-continental United States but less than Se concentrations reported from the Great Lakes region. We found that the liver cadmium (Cd) concentration for males was significantly higher than that for females. Gender differences in hepatic Cd concentrations have not been previously reported for lesser scaup, but Cd is known to have negative impacts on male reproduction. Our results indicate that lesser scaup migrating through the upper Midwest in spring have elevated Se levels and that males carry a significantly greater Cd burden than females. Moreover, elemental concentrations might be high enough to affect reproduction in both male and female lesser scaup, but controlled laboratory studies are needed to adequately assess the effects of Se and Cd on lesser scaup reproduction.

Evaluation of analytical methods for the determination of moisture, crude protein, crude fat, and crude fiber in distillers dried grains with solubles.

A number of analytical methods for constituents commonly measured in distillers dried grains (DDG) are practiced in laboratories serving the agricultural sector. A large interlaboratory variability among results has been observed in the industry. Methods for moisture, crude fat, and crude fiber are empirical, thus part of this variability can be attributed to the use of different methods of analysis. A study was organized and supported by the American Feed Industry Association, the Renewable Fuels Association, and the National Corn Grain Association to evaluate the efficacy, applicability, and the intralaboratory variation of a number of methods for moisture, crude protein, crude fat, and crude fiber in DDG with solubles (DDGS). The moisture methods included in the study are AOAC 930.15, AOAC 934.01, AOAC 935.29, AOAC 2003.06, and National Forage Testing Association (NFTA) 2.2.2.5; the crude protein methods studied are AOAC 990.03 and AOAC 2001.13; the crude fat methods studied are AOAC 945.16, AOAC 954.02, AOAC 2003.05, and AOAC 2006.06; and the crude fiber methods studied are AOAC 978.10 and AOCS Ba 6a-05. A second study was undertaken to assess existing interlaboratory variation of the same methods in 23 laboratories. Based on the results of these studies, the sponsoring associations established recommended reference methods for use in commercial trade of DDGS. The reference methods selected are NFTA 2.2.2.5 for moisture, AOAC 990.03 and AOAC 2001.11 for crude protein, AOAC 945.16 for crude fat, and AOAC 978.10 for crude fiber.

Determination of oxytetracycline/oxytetracycline hydrochloride in animal feed, fish feed, and veterinary medicinal products by liquid chromatography with fluorescence detection: collaborative study.

A method for determining oxytetracycline (OTC) in animal feed, fish feed, and veterinary medicinal products at medicated use and contamination levels was collaboratively studied. The method is applicable to the analysis of animal feeds and mineral premixes containing levels > or =2 mg/kg, and fish feed containing levels > or =10 mg/kg. Oxytetracycline hydrochloride (OTC.HCI) is extracted from ground feed material in acid-methanol solution using mechanical agitation. After centrifugation for 5 min at 1230 x g, an aliquot of the extract is diluted with water andlor acid-methanol so that the concentration of OTC.HCI is approximately the same as that in the working standard, and the solutions contain at least 50% water. Injectable veterinary medicinal materials (also called animal remedy materials) are diluted with water andlor extractant to reach the target concentration. The extracts are filtered and analyzed by reversed-phase liquid chromatography with fluorescence detection with excitation at 390 nm and emission at 512 nm. Twenty-eight test samples of medicated feeds, supplements, and drug premixes, including 4 test samples for trace-level analysis, were sent to 17 collaborators in Canada, The Netherlands, and the United States. Results were received from 11 laboratories. The RSDr values (within-laboratory repeatability) ranged from 1.26 to 9.21%; RSDR values (among-laboratory reproducibility) ranged from 2.14 to 12.9%, and HorRat values ranged from 0.54 to 3.02. It is recommended that this method be adopted AOAC Official First Action.

Multiresidue mycotoxin analysis in corn grain by column high-performance liquid chromatography with postcolumn photochemical and chemical derivatization: single-laboratory validation.

A multiresidue method was developed and validated for simultaneous analysis of 5 families of mycotoxins in corn grain. Deoxynivalenol (DON); aflatoxins B1, B2, G1, G2; ochratoxin A; zearalenone; and fumonisins FB1 and FB2 are extracted from corn grain samples with water-methanol, and extracts are cleaned up using immunoaffinity and solid-phase extraction columns. The column high-performance liquid chromatographic method uses postcolumn photochemical derivatization for detection of aflatoxins and derivatization with o-phthalaldehyde for detection of fumonisins. Mean recoveries and relative standard deviation values (%) over studied fortification levels for the chosen matrixes were: DON 89.9, 8.7; aflatoxin B1 85, 9.4; aflatoxin B2 82.4, 9.7; aflatoxin G1 74.8, 13.5; aflatoxin G2 79.2, 10.0; fumonisin B1 96.2, 8.0; fumonisin B2 84.5, 6.4; zearalenone 91.7, 11.5; and ochratoxin A 87.4, 15.8. The method performance criteria, including specificity, accuracy, repeatability, operational range, and detection limits, were found to be within specifications set by the Feed Additives and Contaminants Group of the AOAC Agricultural Materials Community.

Single-laboratory validation for the quantification of neomycin B and neomycin C in animal feeds by liquid chromatography fluorescence detection with post-column derivatization.

A method using ion-exchange liquid chromatographic (LC) separation, post-column derivatization, and fluorescence detection to quantify neomycin B and neomycin C in animal feeds has been developed and validated. Improved methodology is required to achieve positive identification of antibiotics present and to more accurately determine the amount of antibiotics in feeds. The method sample range covers additive levels found in type A, B, and C medicated feed products (50-0.005% wt/wt neomycin base). The linear range for the method covers 50-150% of expected sample concentrations. Average recovery from type A and B feeds, n = 9, was 100.4% neomycin with %RSD = 2.28. Average recovery from type C feeds and milk replacers, n = 9, was 97.5% neomycin with %RSD = 4.36. There were no interferences from soybean meal and milk replacer matrix components, oxytetracycline, or other aminoglycosides, with the exception of one gentamicin isomer, which co-elutes with neomycin B. However, neomycin and gentamicin are not a legal feed combination, and the presence of gentamicin can easily be discerned by the appearance of the 3 gentamicin homologs that do not interfere. Comparison of the proposed LC method to the microbiological method shows that the LC method provides comparable recoveries of neomycin from feed products throughout the range of concentrations found commercially.

Evaluation of the Use of Microtracers™ in a Proficiency Testing Program.

Background: An effective proficiency testing program must utilize accurate splitting procedures to ensure that customers receive equivalent (by some measure) test items. When test items are not equivalent, it becomes impossible to separate variation among laboratories from variation among test items, and the program cannot achieve its objectives. Therefore, there is a critical need to validate the splitting process used to manufacture test items. Objective: The incorporation of MicrotracersTM was investigated for validating the splitting process used in the Association of American Feed Control Officials Proficiency Testing Program and as a potential quality control event for a production run. Methods: Microtracers were incorporated into six production runs. From each run, 12 test items were randomly selected for evaluation. Proficiency test materials were prepared from commercially available feedstuffs using base animal feeds and feed additives. The tracers were incorporated into base feed with other additives, recovered, and counted from the randomly selected test items. Results: Uniformity of test items was evaluated with the following two statistical methods: (1) relative standard deviation (RSD) of particle counts according to a Poisson distribution and (2) a Pearson's Chi-square test. RSDs for counts (per mass basis) ranged from 2.49 to 4.13%, and Chi-square P values ranged from 0.0097 to 0.3740 over the six sets. Conclusions: Microtracers were determined to be a potential tool for validating the splitting process used to manufacture proficiency test items and a tool for incorporating quality control events into the manufacture of proficiency test items. Highlights: The authors offer suggestions for proficiency testing programs.

Determination of Nitrogen, Phosphorus, and Potassium Release Rates of Slow- and Controlled-Release Fertilizers: Single-Laboratory Validation, First Action 2015.15.

A previously validated method for the determination of nitrogen release patterns of slow- and controlled-release fertilizers (SRFs and CRFs, respectively) was submitted to the Expert Review Panel (ERP) for Fertilizers for consideration of First Action Official Method(SM) status. The ERP evaluated the single-laboratory validation results and recommended the method for First Action Official Method status and provided recommendations for achieving Final Action. The 180 day soil incubation-column leaching technique was demonstrated to be a robust and reliable method for characterizing N release patterns from SRFs and CRFs. The method was reproducible, and the results were only slightly affected by variations in environmental factors such as microbial activity, soil moisture, temperature, and texture. The release of P and K were also studied, but at fewer replications than for N. Optimization experiments on the accelerated 74 h extraction method indicated that temperature was the only factor found to substantially influence nutrient-release rates from the materials studied, and an optimized extraction profile was established as follows: 2 h at 25°C, 2 h at 50°C, 20 h at 55°C, and 50 h at 60°C.

Determination of Phosphorus and Potassium in Commercial Inorganic Fertilizers by Inductively Coupled Plasma-Optical Emission Spectrometry: Single-Laboratory Validation, First Action 2015.18.

A previously validated method for the determination of both citrate-EDTA-soluble P and K and acid-soluble P and K in commercial inorganic fertilizers by inductively coupled plasma-optical emission spectrometry was submitted to the expert review panel (ERP) for fertilizers for consideration of First Action Official Method(SM) status. The ERP evaluated the single-laboratory validation results and recommended the method for First Action Official Method status and provided recommendations for achieving Final Action. Validation materials ranging from 4.4 to 52.4% P2O5 (1.7-22.7% P) and 3-62% K2O (2.5-51.1% K) were used for the validation. Recoveries from validation materials for citrate-soluble P and K ranged from 99.3 to 124.9% P and from 98.4 to 100.7% K. Recoveries from validation materials for acid-soluble "total" P and K ranged from 95.53 to 99.40% P and from 98.36 to 107.28% K. Values of r for citrate-soluble P and K, expressed as RSD, ranged from 0.28 to 1.30% for P and from 0.41 to 1.52% for K. Values of r for total P and K, expressed as RSD, ranged from 0.71 to 1.13% for P and from 0.39 to 1.18% for K. Based on the validation data, the ERP recommended the method (with alternatives for the citrate-soluble and the acid-soluble extractions) for First Action Official Method status and provided recommendations for achieving Final Action status.