Thread: Compost FAQs
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Old 02-22-2004, 06:06 PM
yardmonkey yardmonkey is offline
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Join Date: May 2000
Location: Norman, Oklahoma
Posts: 337
Compost Using FAQ - Part 3

Marc asks an excellent question:

MR>I am confused about peat moss not being a good source of
plant food.
>It is dead vegetation so why no food value? Why is it not
the same as composted vegetation?

Hi Marc,

It is not so much that peat has *no* food value, just that it
has very lttle. The nitrogen level in compost, for example
ranges from .8% up to 2%. Uncomposted manures and other high N
products can N levels around 1% for horse manure through 3% for
dairy manure up to 8% for human manure.

The N level in peat moss is typically below .1%, less than
1/20th of a well made compost. The P and K values are not so
much lower than compost, but these minerals are typically low
in organic sources from plants anyway.

Peat is accumulated from a single source moss, typically
sphagnum, reed-sedge, or hypnum which are mostly fiber, low in
nutrients. Depending on where and how it was mined, it may
have mineral contents from 80% (mostly soil) to 10% (true
moss). It takes thousands of years for peat to accumulate and
when the mosses die, they fall into the soil to decompose very
slowly. Since mosses grow in wetlands, the decomposition is
anaerobic, and anaerobes are notoriously poor at attacking
carbon like the aerobes are. What little N is there is used
within a few decades to support the meager anaerobe population,
after which time the moss just sits there, concentrating.

When humans come in and mine the peat, the degree of
mineralization is dependent on where in the bog, which can
often be up to 40 feet deep, the peat was removed. The top few
feet is mostly living moss, the next layer is the peat we are
used to purchasing, and the lower layers are more of a
texture-less muck, high in mineral content, not unlike a black
topsoil. Of course sphagnum behaves differently from the other
mosses and each bog is unique.

When the peat is mined, it is then used in various soil mixes
or as a landscaping amendment. It is then exposed to N from
the other soil it is blended with and the aerobic decomposition
process begins. This actually starts the peat to compost in a
manner of speaking, although it is actually a poor source of
carbon for composting since it is in a physical structure that
is resistant to microbial attack due to the cell structure of
the moss.

As an organic matter substrate for soil amending, particularly
for helping a soil drain or hold water, it is equal to compost
or manures, perhaps better in some respects. As a food source
for a healthy soil ecosystem, it is rather inert and low in
value. Compost is a true bacteria food and immediately
stimulates active beneficial soil cultures which in turn
produce pheromes and other beneficial byproducts not measured
by NPK or humus analysis.

I treat peat like an organic mineral, an inert buffer with low
value other than its physical structure. As an
environmentalist, I oppose the wanton mining of wetlands and
the indifference of highway designers and farmers in draining
peatlands. Over 90% of the reed-sedge peat resources in the 48
states are lost or severely damaged, particularly in the
mountain states. Most uses of peat would be better served by
recycled products such as bark and compost. I only use peat
for certain planter mixes when I can find no substitute.

MR>I read that it will slowly disappear in the soil over time.
What happens to it? Does it make the soil more acid?

Peat, like all organic matter, oxidizes in the soil over time
leaving various humus compounds. The chemistry is basically
one mole of CO2 and one mole of heat is produced by bacterial
action (composting) or chemical oxidation. Its acidification
properties depend on the source and initial pH level of the
peat. Some sphagnum peat is in the high 4 range, some sedges
are neutral or even alkaline. There is no way to know the acid
properties of a particular peat without a pH test. The
acidification effect is also lost over time, depending on the
ambient pH level and other soil conditions.

MR>Gardening books are not clear on this.

They are not clear on most issues related to the use of organic
matter in any of its forms. They tend to be chemically focused
with the notion that all soil is inert media, a necessary evil,
which is used to hold roots in order to feed the plant with
chemicals. Hydroponic gardening with rock wool and chemical
solutions is the ultimate example of this narrow view of the
humusphere and its relationship with plant growth. The carbon
respiration cycle is rarely taught in schools, whereas the
cycle of H2O from surface water to clouds is universally taught.

The carbon cycle goes from atmospheric CO2 to plants to humus
and back to CO2.

Hope this helps.

Mr Compost~~~
* May 8th - Let's see what this one does... &%$/()"@# NO
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