[compost_tea] Re: Inclusion of clay in compost

From: Tom Jaszewski <tom_at_livesoil.com>
Date: Mon, 07 Feb 2005 16:49:32 -0000

--- In compost_tea_at_yahoogroups.com, willfindley@a... wrote:
> How do you measure moisture content and CO2 content?
> Thanks,
> Bill in AL



More accurate means of measuring moisture content exist. The most
frequently used method is a "gravimetric" procedure of weighing
samples before and after the water is removed. The basic concept of
this procedure is: A sample of the material is weighed to determine
its wet weight (minus the weight of the container). Then the sample
is dried to the point where all or nearly all of the water is
evaporated and the sample is weighed again. This weight (minus the
weight of the container) is the dry weight. The difference between
the wet and dry weights is the weight of the water that the sample
originally contained. Dividing the water weight by the wet weight
gives the moisture content as a fraction. This type of calculation is
known as the "wet basis", or: 

Percent Moisture = [100% x water weight (grams)] / wet weight (grams)

The primary pitfall in this gravimetric procedure is the loss of
volatile compounds in the compost during drying. This can be
minimized by the drying procedure used. Drying methods include air
drying, oven drying at various temperatures, and microwaves.
Microwaves are the quickest and most convenient but also the least
accurate. Air drying is slow but most accurate if the material is not
actively decomposing. Oven drying is the middle ground and tends to
be the standard.

The EPA standard method for determining moisture content is to dry
the sample in a vented oven at 103 to 105o C (217 to 221oF) until the
sample stops losing weight. The method adopted by the U.S. Composting
Council's Test Methods for the Examination of Composting and Compost
requires oven drying at 65 to 75o C (149 to 167o F) until no change
in weight is observed. As the temperature range in the EPA method is
above the boiling point of water, drying is relatively quick (1-2
hours). At the TMECC-recommended procedure, drying may take one or
two days. The advantage of the lower drying temperature is to
minimize the loss of volatile compounds. 







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Received on Mon Feb 07 2005 - 14:57:46 EST

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