AOAC ERP Fertilizers - December 2017

AOAC Official Method 2015.15 Nitrogen, Phosphorus, and Potassium Release Rates of Slow- and Controlled-Release Fertilizers First Action 2015 [Applicable for the determination of extractable N, P (as P 2 O 5 ), and K (as K 2 O) and cumulative N, P, or K release in slow-release fertilizers (SRFs) and controlled-release fertilizers (CRFs).] A. Principle InAlternativeA, a representative unground test portion is exposed to ambient temperature extractions of a solvent in a biologically active sandy soil medium. In Alternative B, a representative unground test portion is exposed to increasingly aggressive solvent temperature extractions. Extractions are designed to extract and isolate nutrients becoming available over time. Each extract is analyzed by AOAC procedures for the nutrient of interest (total N, P, and K). Along with analyses of total nutrients and reference materials, data are used to develop information specific to the cumulative percentage of nutrient released over time. Alternative A: 180 Day Extraction at Ambient Temperature B. Apparatus ( a )  Extraction columns .—Extraction columns (incubation lysimeters; see Figure  2015.15A ) are constructed of PVC pipe (30 × 7.5 cm) fitted with a fiberglass mat in the bottom held in place by a 7.5 in. id PVC cap. The cap is fitted with a barbed plastic fitting, and vacuum tubing attached for leachate collection. A PVC cap is used on the top with no hole, but with a coating of stopcock grease to cap the lysimeter. All columns are supported on a wood frame. ( b )  Beaker .—A 50 mL beaker is placed in the headspace of each incubation lysimeter. ( c )  Filtering flasks .—Filtering flasks with a one-hole stopper are placed beneath the leaching columns and attached to the vacuum tubing. A pinch clamp is used to prevent leaks when filtration and leachate collection is complete. ( d )  Vacuummanifold .—Vacuummanifold and tubing connecting each flask to a standard laboratory vacuum pump. ( e )  Riffle.— Gated or rotary. C. Reagents and Reference Materials ( a )  Extraction solution .—0.01% (w/v) citric acid [2 g/20 L deionized water (DI)] prepared from reagent-grade citric acid.

( b )  Ammonia trap solution .—0.2 M H 2 SO 4 solution. ( c )  Loamy, siliceous, hyperthermic, Grossarenic Paleudult soil .—Arredondo fine sand. Particle size analysis is shown in Table  2015.15A . ( d )  Uncoated quartz sand United States Golf Association Greens ( USGA Mix) .—Topdress sand (noncoated quartz), 20/30 silica sand. Available from Edgar Minerals Inc. (Edgar, FL, USA) and Standard Sand and Silica Co. (Lynne, FL, USA). Particle size analysis is shown in Table 2015.15B . ( e )  Soil media .—Mixture of 1710 g uncoated quartz sand, C(d) , and 90 g loamy siliceous, hyperthermic, Grossarenic Paleudult soil, C(c) , or similar type of local soil acting as a microbial inoculum. D. Sample Preparation ( a )  For granular materials .—Using a gated riffle splitter, reduce laboratory sample to yield an unground representative test portion containing approximately 450 mg of total N to mix thoroughly with the soil–sand mixture. If no N is present, a 3 (±0.1) g test portion should be used. Note : Quick-release N must be limited to 600 mg N/test portion to prevent ammonia buildup in the column (thus preventing an active biological system); however, when doing so, replicates must be used to cumulatively measure at least 3.0 g total test portion mass and averaged to generate a single result. If soluble N is not limiting, 5–6 g unground fertilizer should be used for the test portion. ( b )  For liquid materials .—Assure the material is properly mixed and extract via pipet a representative test portion containing approximately 450 mg total N. Mix thoroughly with the soil/sand Table 2015.15A. Particle size analysis of Arredondo fine sand a Mesh (U.S.) b Opening, mm Retained, % Cumulative, % 5 4.000 0.0 0.0 10 2.000 0.4 0.4 20 0.850 1.2 1.6 40 0.425 12.4 14.0 100 0.150 68.7 82.7 200 0.075 14.5 97.2 −200 2.8 100.0 a  Actual data, not specifications. b  United States Standard Mesh—ASTM E11:01. Table 2015.15B. 20/30 particle size analysis of Topdress sand a Mesh (U.S.) b Opening, mm Retained, % Cumulative, % 5 4.000 0.0 0.0 10 2.000 0.0 0.0 20 0.850 11.6 11.6 40 0.425 34.2 45.9 100 0.150 51.9 97.8 200 0.075 2.2 99.9 −200 0.1 100.0 a  Actual data, not specifications. b  United States Standard Mesh—ASTM E11:01.

Figure 2015.15A. Incubation lysimeters.

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