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Agricultural Service Laboratory
Compost Analysis Procedures
May 15, 2004
TABLE OF CONTENTS
Sample Preparation
Ammonium-Nitrogen Determination
Total Nitrogen and Total Carbon
Mineral Analysis
Organic Matter
EC (Soluble Salts) and pH
Nitrate Nitrogen
Bulk Density
Sample Preparation
- 1 pint of sample is required for analysis
- Laboratory numbers are assigned to the sample submission
form and the data sheet. The lab numbers are written on the sample bags with
a sharpie. The first digit of the lab number is 4. The next two digits are
the month. The last four digits are the sample number for the year.
- Record tare weight of paper bag. Add 100 – 200 g
sample, weigh and record wet weight. Place in the oven to dry at 60 degrees C
overnight. Record dry weight. Grind for nitrogen, carbon, mineral, organic
matter, and nitrate nitrogen analyses. Record weight of 100 mL beaker. Add
about 5 g dried and ground sample and record weight. Dry at 105 degrees C for
3 hours. Record weight to get total dry matter.
Analyses
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Ammonium-Nitrogen Determination (report 2 decimal
places for solids).
Weigh about 2 grams of a
representative sample into a tared Erlenmeyer flask. Record weight on flask to
2 decimal places. Add 20 mL 2 M KCl. Shake for 30 min. Filter sample
into digestion tube. Transfer weight to tube. Enter weight into distillation
unit. Distill Sample. Titrate with H2SO4 solution using the boric acid
indicator. Record value to 2 decimal places.
To make 2 M KCl, weigh
298.24 g KCl into a 2 L volumetric flask. Dilute to volume with deionized H2O.
Ref: Delaware.
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Total Nitrogen and Total Carbon
Analyze dried and ground sample according to
Elementar procedure. Record value to 2 decimal places.
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Mineral Analysis
Wet ash dried and ground sample
according to plant tissue procedure. Record results according to plant tissue
procedure.
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Organic Matter
Number porcelain crucibles with wax pencil. Weigh
crucibles to 4 decimal places. Scoop dried and ground samples into crucibles
using 5 g soil scoop. Put crucibles plus samples on tray in furnace. Set
temperature to 105 degrees C. Ash at this temperature for 2 h. (It takes 15
minutes for the furnace to reach this temp, so set the dial at 105 for a total
of 2 h and 15 min.)
Remove samples from furnace with
tongs, place in desiccator, and weigh to 4 decimal places immediately while
still warm so moisture won’t be absorbed. Replace crucibles plus samples in
furnace. Turn dial up to 360 degrees C.
Ash at this temp for 2 hours. (It
takes ˝ hour for the furnace to reach this temperature, so set the dial at 360
for a total of 2˝ hour.) Turn furnace off and open door. Place samples in
desiccator with tongs and allow samples to cool. Weigh samples to 4 decimal
places.
Calculate OM% and record on data
sheet with one decimal.
Crucible wt = a
Crucible wt + sample wt after 105 heating = b
Crucible wt + sample wt after 360 heating = c
%OM = ((b-a)-(c-a))(100)/(b-a)
Reference
E. E. Schulte, Recommended Soil
Organic Matter Tests.
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EC (Soluble Salts) and pH
These tests are performed on the
as-received sample on a 1:5 (w/w) basis. First determine the moisture content.
Then weigh (in a tared 800 mL plastic beaker) the equivalent wet weight to give
20 g of dry weight material (e.g. if the moisture is 50%, weight out 40 g fresh
to get 20 g dry material). Add water to bring final weight to 120 g. This will
give a total of 20 g of material and 100 mL water for a ratio of 1:5. Stir and
let sit for 1 hour. Filter with screen filter. Measure EC and pH according to
procedure on extract. Record EC to 2 decimal places and pH to 1 decimal place.
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Nitrate Nitrogen
Analyze according to animal waste
procedure. Record to 0 decimal places.
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Bulk Density (Volume Basis)
Spread about 3 liters of media in soil tray and dry
overnight at 80 degrees C.
Measure out and weigh five – 500 mL amounts in a 600 mL beaker. Average the 5
values. Multiply averaged value by 3.38 to get lbs/cubic yd.
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