Methods to be Reviewed by OMB in 2016

(a)

Extraction solution

.—0.01% (w/v) citric acid (2 g/20 L deionized water).

(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

.—Topdress sand (noncoated quartz), 20/30 silica sand. Available from

Edgar Minerals Inc., Edgar, FL and Standard Sand and Silica Co., Lynne, FL. Particle size analysis is

shown in Table

2015.15B

(e)

Soil media

.—Mixture of 1710 g uncoated quartz sand (United States Gold Association

Greens Mix), [D(

)] and 90 g loamy siliceous, hyperthermic, Grossarenic Paleudult soil [D(

)] or

similar type of local soil acting as a microbial inoculum.

E. Sample Preparation of 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.

F. Procedure

Test portions from each material to be tested are placed in incubation columns held at room

temperature (20–25°C). The sand/soil/test portion mixture is brought to 10% gravimetric

moisture by adding 180 mL 0.01% citric acid. A 50 mL beaker containing 20 mL 0.2 M H 2 SO 4 is

placed in the headspace of the

column as an ammonia trap. The solution in the ammonia trap

replaced and analyzed for NH 4 -N by titration every 7 days. After 7, 14, 28, 56, 84, 112, 140, and

180 days, each column is leached at the same time of day with one pore volume (500 mL) 0.01%

citric acid using a vacuum manifold. Vacuum is pulled

for 2 min to ensure all free extraction

solution is removed. Mix well and transfer to a 250 mL graduated cylinder. Record the leachate

volume and remove aliquots to test for total N. In addition, measure the pH and EC of the

leachate. Retain the remaining leachate in reserve in case an additional or recheck analysis is

required. Store in dark bottles and freeze if retained for more than 7 days. (

Note

: If no volatile

N is detected in the ammonia trap during the first two sampling periods, the NH 4

trap can be

removed and analysis discontinued.)

G. Analytical Determinations

(a) Determine total N on each of the extracts obtained using AOAC Method

993.13

(combustion) or

978.02

(modified comprehensive; 1), or equivalent, applicablemethods validated

in your laboratory. Utilize an applicable method matched reference material in each run. Utilize at

least three standards appropriate for the range of extract concentrations. Typically a combination of

10, 100, and 1000 mg N/L cover the range of N in the extracts.

Candidates for 2016 Method of the Year

209