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Making and Using Composts
The reason of our thus treating composts of various
soils and substances, is not only to dulcify,
sweeten, and free them from the noxious qualities they otherwise
retain . . .
[Before composting, they are] apter to ingender vermin, weeds,
and fungous . . . than to produce wholsome [sic]
plants, fruits and roots, fit for the table.
J. Evelyn, seventeenth century
Decomposition of organic materials takes place naturally
in forests and fields all around us. Composting is the art and science
of combining available organic wastes so that they decompose to
form a uniform and stable finished product. Composts are excellent
organic amendments for soils. Composting reduces bulk, stabilizes
soluble nutrients, and hastens the formation of humus. Most organic
materials, such as manures, crop residues, grass clippings, leaves,
sawdust, and many kitchen wastes, can be composted.
The microorganisms that do much of the work of rapid
composting need high temperatures, plenty of oxygen, and moisture.
These heat-loving, or thermophilic, organisms work best between
about 110 and 130°F. Temperatures above 140°F can develop
in compost piles, helping kill off weed seeds and disease organisms,
but this overheating usually slows down the process. At temperatures
below 110°F, the less active meso-phylic organisms take over
and the rate of com-posting again slows down. The com-posting process
is slowed by anything that inhibits good aeration or the maintenance
of high enough temperatures and sufficient moisture.
Composting farm wastes and organic residues from off
the farm has become a widespread practice. Accepting and composting
lawn and garden wastes provides some income for farmers near cities
and towns. They may charge for accepting the wastes and for selling
compost. Some farmers, especially those without animals or sod crops,
may want to utilize the compost as a source of organic matter for
their own soils.
Types of "Composting"
Some people talk about "low temperature"
composting different types are called "sheet," worm
(vermicomposting), small pile composting and "high temperature"
com-posting. We like to use the term composting only when
talking about the rapid decomposition that takes place at
high temperatures. |
Making Composts
Moisture
The amount of moisture in a compost pile is important. If the materials
mat and rainwater can't drain easily through the pile, it may not
stay aerobic in a humid climatic zone. On the other hand, if composting
is done inside a barn or under dry climatic conditions, the pile
may not be moist enough to allow microorganisms to do their jobs.
Moisture is lost during the active phase of composting, so it may
be necessary to add water to a pile. In fact, even in a humid region,
it is a good idea to moisten the pile at first, if dry materials
are used. However, if something like liquid manure is used to provide
a high-nitrogen material, sufficient moisture will most likely be
present to start the composting process. The ideal moisture content
of composting material is about 40 to 60 percent, or about as damp
as a wrung-out sponge. If the pile is too dry 35 percent or less
ammonia is lost as a gas and beneficial organisms don't repopulate
the compost after the temperature moderates. Very dry, dusty composts
become populated by molds instead of the beneficial organisms we
want.
Types of Starting Materials
The organic materials used should have lots of carbon and nitrogen
available for the microorganisms to use. High-nitrogen materials,
such as chicken manure, can be mixed with high-carbon materials
like hay, straw, leaves, or sawdust. Compost piles are often built
by alternating layers of these materials. Turning the pile mixes
the materials together. Manure mixed with sawdust or wood chips
used for bedding can be composted as is. Composting occurs most
easily if the average C:N ratio of the materials is about 25 to
40 parts carbon for every part nitrogen (see chapter
8 for a discussion of C:N ratios).
There are too many different types of materials that
you might work with to give blanket recommendations about how much
of each to mix to get the moisture content and the C:N into reasonable
ranges so the process can get off to a good start. One example is
given in the box on the following page.
Even Birds Do It?
The male brush turkey of Australia gathers leaves,
small branches, moss, and other litter and builds a mound
about 3 feet high and 5 feet across. It then digs holes into
the mound repeatedly and refills them helping to fragment
and mix the debris. Finally, the pile is covered with a layer
of sticks and twigs.
The female lays her eggs in a hole dug into the pile, which
heats up to close to 100°F around the eggs while the
outside can be around 65°F. The heat of the composting
process frees the birds from having to sit on the eggs to
incubate them.
-- Seymore, 1991 |
Cornell University's web site for composting issues
(http://www.css.cornell.edu/compost/Composting_Homepage.html)
features formulas to help you estimate the different proportions
of the specific materials you might want to use in the compost pile.
Sometimes it will work out that the pile may be too wet, too low
in C:N (that means, too high in nitrogen), or too high in C:N (low
in nitrogen). To balance your pile, you may need to add other materials,
or change the ratios used. The examples given above can be remedied
by adding dry sawdust or wood chips in the first two cases and nitrogen
fertilizer in the third. If a pile is too dry, you can add water
with a hose or sprinkler system.
A Sample Compost Recipe
Start with:
a) grass clippings (71% moisture, 45% C, and 2.4% N)
b) leaves (35% moisture, 50% C, and 0.75% N)
c) food scraps (80 % moisture, 42% C, and 5.0% N)
The ratio of the materials needed
to get 60 percent moisture and 30:1 C:N is:
d) 100 lbs. of grass, 130 lbs. of leaves, and 80 lbs. of food
scraps.
-- Richard, Trautmann & Krasny, 1996 |
One thing to keep in mind is that not all carbon is
equally available for microorganisms. Lignin is not easily decomposed
(we mentioned this when discussing soil organisms in chapter
3 and again in chapter 8, when we talked
about the different effects that various residues have when applied
to soil). Although some lignin is decomposed during composting probably
depending on factors such as the type of lignin and the moisture
content -- high amounts of carbon present as lignin may indicate
that not all of carbon will be available for rapid composting. When
residues contain high amounts of lignin, it means that the effective
C:N can be quite a bit lower than indicated by using total carbon
in the calculation (table 12.1). For some materials, there is little
difference between the C:N calculated with total carbon versus using
only biodegradable carbon.
It's a good idea to avoid using certain materials,
such as coal ash, wood chips from pressure-treated lumber, manure
from pets, and large quantities of fats, oils, and waxes. These
types of materials are either difficult to compost or may result
in compost containing chemicals that can harm crops.
Wood chips or bark are sometimes used as a bulking
agent to provide a "skeleton" for good aeration. These
materials may be recycled by shaking the finished compost out of
the bulking material, which can then be used for a few more composting
cycles.
Composting Animals
It is also possible to compost dead farm animals,
which are sometimes a nuisance to get rid of. Chickens and
even dead cows have been successfully composted. Cam Tabb,
a West Virginia dairy and crop farmer, starts the process
for large animals by laying the carcass that's been in the
open for one day on a 3 to 4 ft bed of sawdust. Then he covers
it with 3 to 4 ft of sawdust/horse manure and then turns the
pile in 3 to 4 weeks. After all turning is done, he uses new
base material on top. |
Pile Size
A compost pile is a large natural convective structure something
like many chimneys all next to each other moving oxygen into the
pile as carbon dioxide, moisture, and heat rise from it. The materials
need to fit together in a way that allows oxygen from the air to
flow in freely. On the other hand, it is also important that not
too much heat escape from the center of the pile. If small-sized
particles are used, a "bulking agent" may be needed to
make sure that enough air can enter the pile. Sawdust, dry leaves,
hay, and wood shavings are frequently used as bulking agents. Tree
branches need to be "chipped" and hay chopped so that
it doesn't mat and slow composting. Composting will take longer
when large particles are used, especially those resistant to decay.
The pile needs to be large enough to retain much of
the heat that develops during compost-ing, but not so large and
compacted that air can't easily flow in from the outside. Compost
piles should be 3 to 5 feet tall and about 6 to 10 feet across the
base after the ingredients have settled (see figure 12.1). (You
might want it on the wide side in the winter, to help maintain the
warm temperatures, while gardeners can make compost in a 3-feet
tall by 3-feet wide pile in the summer.) Easily condensed material
should initially be piled higher than 5 feet. It is possible to
have long windrows of composting materials, as long as they are
not too tall or wide.
Minimum Turning Technique
Farm-quality composts can be produced by turning
the pile only once or twice. To do this you need to carefully
construct the pile building it up to reasonable dimensions,
using and thoroughly mixing materials that give very good
porosity, and making sure the pile stays moist. |
Turning the Pile
Turning the composting residues exposes all the materials to the
high-temperature conditions at the center of the pile. Although
the materials at the top and on the sides of the pile are barely
composting, they do provide insulation for the rest of the pile.
Turning the pile rearranges all the materials and creates a new
center. If piles are turned every time the interior reaches and
stabilizes at about 140°F for a few days, it is possible to
complete the composting process within months. On the other hand,
if you only turn the pile occasionally, it may take a year or longer
to complete. Equipment is now available to quickly turn long compost
windrows at large-scale composting facilities. Tractor-powered compost
turners designed for composting on farms are also available.
Although turning compost frequently speeds up the
process, it may also dry out the pile and cause more nitrogen loss.
If the pile is too dry you might consider turning it when it's raining
to help moisten it. If the pile is very wet, you might want to turn
it on a sunny day. Very frequent turning may not be advantageous,
because it can cause physical breakdown of important structural
materials that aid natural aeration. The right amount of turning
depends on a variety of factors, such as aeration, moisture, and
temperature. Turn your compost pile to avoid cold, wet centers,
break up clumps, and make the compost more uniform later in the
process before use or marketing.
|
Figure 12.1 Compost pile
dimensions and turning techniques. |
The Curing Stage
Following high-temperature composting, the pile should be left to
cure for about one to three months. Usually this is done once pile
temperatures reach 105°F and high temperatures don't reoccur
following turning. Curing is especially needed if the active (hot)
process is short or poorly managed. There is no need to turn the
pile during curing because you are not trying to stimulate maximum
decomposition and there is less need for rapid oxygen entry into
the pile's center when decomposition rate is slow. [However, the
pile may still need turning during the curing stage if it is very
large or it didn't really finish composting (determining when compost
is finished is sometimes difficult), or if the pile is soaked by
rain.] Curing the pile furthers aerobic decomposition of resistant
chemicals and larger particles. Common beneficial soil organisms
populate the pile during curing, the pH becomes closer to neutral,
and ammonium is converted to nitrate. Be sure to maintain water
content around 50 percent during curing to ensure that active populations
of beneficial organisms develop.
It is thought that the processes that occur during
the early curing process give compost some of its disease-suppressing
qualities. On the other hand, beneficial organisms require sources
of food to sustain them. Thus, if composts are allowed to cure for
too long depleting all the available food sources disease suppression
qualities may decrease and eventually be lost.
Disease Suppression by
Composts
Research by Harry Hoitink and co-workers at
Ohio State University shows that composts can suppress root
and leaf diseases of plants. This suppression comes about
because the plants are generally healthier (microorganisms
produce plant hormones as well as chelates that make micronutrients
more available) and, therefore, are better able to resist
infection. Beneficial organisms compete with disease organisms
for nutrients as well as directly consume the disease-causing
organisms or produce antibiotics that kill bacteria. Some
organisms, such as springtails and mites, "actually search
out pathogen propagules in soils and devour them," according
to Hoitink. In addition, he found that potting mixes containing
composts "rich in biodegradable organic matter support
microorganisms that induce systemic resistance in plants.
These plants have elevated levels of biochemical activity
relative to disease control and are better prepared to defend
themselves against diseases." This includes resistance
to both root and leaf diseases.
Composts rich in available nitrogen may actually
stimulate certain diseases, as was found for Phytophthora
root rot on soybeans, as well as Fusarium wilts and fire blight
on other crops. Applying these composts many months before
cropping, allowing the salts to leach away, or blending them
with low nitrogen composts prior to application reduces the
risk of stimulating diseases.
Composting can change certain organic materials
used as surface mulches such as bark mulches from stimulating
disease to suppressing disease. |
Using Composts
Finished composts generally provide only low relative
amounts of readily available nutrients. During composting, much
of the nitrogen is converted into more stable organic forms, although
potassium and phosphorus availability remains unchanged. However,
it should be kept in mind that composts can vary significantly and
some may have high levels of nitrate. Even though most composts
don't supply a large amount of available nitrogen per ton, they
still supply fair amounts of other nutrients in available forms
and greatly help the fertility of your soil by increasing organic
matter and by slowly releasing nutrients. Composts can be used on
turf, in flower gardens, and for vegetable and agronomic crops.
Composts can be spread and left on the surface or incorporated into
the soil by plowing or rototilling. Composts also are used to grow
greenhouse crops and are the basis of some potting soil mixes.
Advantages of Composting
Composted material is less bulky than the original
material, and easier and more pleasant to handle. During the composting
process, carbon dioxide and water are lost to the atmosphere and
the size of the pile decreases by 30 to 60 percent. In addition,
many weed seeds and disease-causing organisms may be killed by the
high temperatures in the pile. Unpleasant odors are eliminated.
Flies, a common problem around manures and other organic wastes,
are much less of a problem with composts. Composting reduces or
eliminates the decline in nitrogen availability that commonly occurs
when organic materials, such as sawdust or straw, are added directly
to soil. Composting is also very useful for recycling kitchen wastes,
leftover crop residues, weeds, and manures. Many types of local
organic waste, such as apple pumice, lake weeds, leaves, and grass
clippings, can be composted.
There is evidence that compost application lowers
the incidence of plant root and leaf diseases (see above). In addition,
the chelates and the direct hormone-like chemicals present in compost
stimulate the growth of healthy plants. Then there are the positive
effects on soil physical properties that are derived from improving
soil organic matter. All of these factors together may help explain
some of the broad benefits to plant growth that are attributed to
compost.
If you have a large amount of organic waste but not
much land, composting may be very helpful. Also, since making compost
decreases the solubility of nutrients, composting may help lessen
pollution in streams, lakes, and groundwater. On many poultry farms
and on beef feedlots, where high animal populations on limited land
may make manure application a potential environmental problem, composting
may be the best method for handling the wastes. Composted material,
with about half the bulk and weight and its higher commercial value
than the manure, can be economically transported significant distances
to locations where nutrients are needed.
Protecting
Drinking Water Supplies
Composting of manure is of special interest
in watersheds that supply drinking water to cities, such as
those that serve New York. The parasites Giardia Lamblia
(beaver fever) and Cryptosporidium parvum cause illness
in humans and are shed through animal manure, especially young
stock. These organisms are very resistant in the environment
and are not killed by chlorination. Composting of manure,
however, is an economical option that kills the pathogen and
protects drinking water. |
Without denying these good reasons to compost, there
are frequently very good reasons to just add organic materials directly
to the soil, without composting. Compared with fresh residues, composts
may not stimulate as much production of the sticky gums that help
hold aggregates together. Also, some uncomposted materials have
more nutrients that are readily available to feed plants than do
composts. If your soil is very deficient in fertility, plants may
need readily available nutrients from residues. Routine use of compost
as an nitrogen source may cause high soil phosphorus levels to develop,
because of the relatively low N:P ratio. Finally, more labor and
energy usually are needed to compost residues before applying than
to simply apply the uncomposted residues directly.
Sources
Hoitink, H.A.J., D.Y. Han, A.G. Stone, M.S. Krause, W. Zhang, and
W.A. Dick. 1997. Natural Suppression. American Nurseryman.
October 1, 1997:9097.
Epstein, E. 1997. The Science of Composting.
Technomic Publishing Company.
Martin, D. L., and G. Gershuny (eds.). 1992. The
Rodale Book of Composting: Easy Methods for Every Gardener.
Rodale Press. Emmaus, PA.
Richard, T.L., N.M. Traubman, and M.E. Krasny. 1996.
Cornell composting website. http://www.css.cornell.edu/compost/Composting_Homepage.html
Rothenberger, R.R., and P.L. Sell. Undated. Making
and Using Compost. University of Missouri Extension Leaflet
(File: Hort 72/76/20M). Columbia, MO.
Rynk, R. (ed.). 1992. On Farm Composting. NRAES-54.
Northeast Regional Agricultural Engineering Service. Ithaca, N.Y.
Seymour, R.S. 1991. The brush turkey. Scientific
American. Dec. 1991.
Staff of Compost Science. 1981. Composting:
Theory and practice for city, industry, and farm. The JG Press.
Emmaus, PA.
Weil, R.R., D.B. Friedman, J.B. Gruver, K.R. Islam,
and M.A. Stine. Soil Quality Research at Maryland: An Integrated
Approach to Assessment and Management. Presented in Baltimore,
MD at the 1998 ASA/CSSA/SSSA meetings. This is the source of the
quote from Cam Tabb.
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