Soil Microbial Ecology - Soil Molecular Ecology Laboratory

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METHOD:
RESPONSE TO CARBON ADDITION
Treatments are Agriculture Soil (alone, with glucose, or with cellulose additions) and
Forest Soil (alone, with glucose, or with cellulose additions).
Each student will do either agriculture soil or forest soil.
Weigh out 50 g (dry mass basis) of soil (soil should be at ca. 10% moisture) and place
in 1 pint Mason jar.
Each soil will receive 2 ml of NH 4 N0 3 solution, 250 mg glucose plus NH 4 N0 3 or 250
mg cellulose powder plus NH 4 N0 3 (note, add dry ingredients and mix before adding
N-solution).
Place a 50 ml beaker on the soil.
Add exactly 10 ml of 1 N NaOH to the 50 ml beaker and seal with the Mason jar lid.
C0 2 produced by the soil is absorbed by the alkali.
After 1 wk of incubation, remove NaOH with a syringe, place in beaker, and recharge
beaker with fresh NaOH for the second wk reading.
To determine the amount of C0 2 produced:
1. Add 1 ml of phenolphthalein and 1 ml of 50% BaCl 2 to the beaker of NaOH to
precipitate the carbonate as an insoluble barium carbonate
2. Titrate to neutralize the unused alkali with 1 N HCl and record the exact used acid
volume.
3. Calculate the amount (mg) of C or C0 2 = (B-V) NE
Note: (B-V) is a simplification of (T-V)-(T-B)
Where: T = Total volume of NaOH at the start of the experiment, V = Volume
(ml) of acid to titrate the alkali in the C0 2 collectors from treatments (i.e., with
glucose and cellulose) to the endpoint, B = Volume (ml) of acid to titrate the
alkali in the CO 2 collectors from controls (i.e., without C addition) to the
endpoint, N = Normality of the acid, and E = Equivalent weight.
If data are expressed in terms of carbon, E=6; if expressed as CO 2 , E=22
4. Express the results as mg carbon dioxide produced per g soil. Show the
calculation, tabulate the class results and discuss.