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