In article ,
Phisherman wrote:

Is there a test to get a percentage of organic matter in a soil
sample? Anyone know how is this typically done in a lab? I was
wondering if the sample is weighed, burned off, and re-weighed to
calculate a percentage?

Yes. The sample should be taken with surface organic material scraped
aside. Sample should be taken from a hole 8" to 12" deep (the material
from that hole is your sample). For organic analysis, the sample would
first need to be dried and weighed, then aerated and held at a temp
greater than 455F for several hours, and then reweighed.

If you put a similar sample in a large jar with water and shake your
sample until it forms a slurry, the sand will fall out after five min.
or so, the silt after 20 min., and the clay after 24 hours (descending
particle size). The height of each band in comparison to the total
sedimentation will give you the approximate composition of your soil.
Good soil will be 20 - 30% clay, 30-50% silt, 30 - 50% sand, and 5 - 10%
organic material.

There is more about microorganisms and their interactions with plants
but I've already gone beyond what you asked.

One cautionary note though, beware chemical fertilizers. This doesn't
come from ridged ideology but from the facts that numero-uno: chemical
fertilizers, used at suggested rates, kill off soil organisms, which
leads to less top soil, which leads to the use of more chemferts to
maintain production, and numero-two-o: the translocation of the nitrogen
to the plants now rapidly growing leaves (nitrogen rich, tender leaves)
makes them a target for garden insects.
--

- Billy
"For the first time in the history of the world, every human being
is now subjected to contact with dangerous chemicals, from the
moment of conception until death." - Rachel Carson

http://www.youtube.com/watch?v=WI29wVQN8Go

http://www.haaretz.com/hasen/spages/1072040.html