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Organic Gardener's
Composting
by Steve Solomon
CHAPTER TWO
Composting Basics
Managing living systems usually goes
better when our methods imitate nature's. Here's an example of what happens when
we don't.
People who keep tropical fish in home
aquariums are informed that to avoid numerous fish diseases they must maintain sterile
conditions. Whenever the fish become ill or begin dying, the hobbyist is advised
to put antibiotics or mild antiseptics into the tank, killing off most forms of microlife.
But nature is not sterile. Nature is healthy.
Like many an apartment dweller, in
my twenties I raised tropical fish and grew house plants just to have some life around.
The plants did fine; I guess I've always had a green thumb. But growing tired of
dying fish and bacterial blooms clouding the water, I reasoned that none of the fish
I had seen in nature were diseased and their water was usually quite clear. Perhaps
the problem was that my aquarium had an overly simplified ecology and my fish were
being fed processed, dead food when in nature the ecology was highly complex and
the fish were eating living things. So I bravely attempted the most radical thing
I could think of; I went to the country, found a small pond and from it brought home
a quart of bottom muck and pond water that I dumped into my own aquarium. Instead
of introducing countless diseases and wiping out my fish, I actually had introduced
countless living things that began multiplying rapidly. The water soon became crystal
clear. Soon the fish were refusing to eat the scientifically formulated food flakes
I was supplying. The profuse variety of little critters now living in the tank's
gravel ate it instead. The fish ate the critters and became perfectly healthy.
When the snails I had introduced with
the pond mud became so numerous that they covered the glass and began to obscure
my view, I'd crush a bunch of them against the wall of the aquarium and the fish
would gorge on fresh snail meat. The angelfish and guppies especially began to look
forward to my snail massacres and would cluster around my hand when I put it into
the tank. On a diet of living things in a natural ecology even very difficult species
began breeding.
Organic and biological farmers consider
modern "scientific" farming practices to be a similar situation. Instead
of imitating nature's complex stability, industrial farmers use force, attempting
to bend an unnaturally simplified ecosystem to their will. As a result, most agricultural
districts are losing soil at a non-sustainable rate and produce food of lowered nutritional
content, resulting in decreasing health for all the life forms eating the production
of our farms. Including us.
I am well aware that these condemnations
may sound quite radical to some readers. In a book this brief I cannot offer adequate
support for my concerns about soil fertility and the nation's health, but I can refer
the reader to the bibliography, where books about these matters by writers far more
sagely than I can be found. I especially recommend the works of William Albrecht,
Weston Price, Sir Robert McCarrison, and Sir Albert Howard.
Making Humus
Before we ask how to compost, since
nature is maximally efficient perhaps it would benefit us to first examine how nature
goes about returning organic matter to the soil from whence it came. If we do nearly
as well, we can be proud.
Where nature is allowed to operate
without human intervention, each place develops a stable level of biomass that is
inevitably the highest amount of organic life that site could support. Whether deciduous
forest, coniferous forest, prairie, even desert, nature makes the most of the available
resources and raises the living drama to its most intense and complex peak possible.
There will be as many mammals as there can be, as many insects, as many worms, as
many plants growing as large as they can get, as much organic matter in all stages
of decomposition and the maximum amount of relatively stable humus in the soil. All
these forms of living and decomposing organisms are linked in one complex system;
each part so closely connected to all the others that should one be lessened or increased,
all the others change as well.
The efficient decomposition of leaves
on a forest floor is a fine example of what we might hope to achieve in a compost
pile. Under the shade of the trees and mulched thickly by leaves, the forest floor
usually stays moist. Although the leaves tend to mat where they contact the soil,
the wet, somewhat compacted layer is thin enough to permit air to be in contact with
all of the materials and to enter the soil.
Living in this very top layer of fluffy,
crumbly, moist soil mixed with leaf material and humus, are the animals that begin
the process of humification. Many of these primary decomposers are larger, insect-like
animals commonly known to gardeners, including the wood lice that we call pill bugs
because they roll up defensively into hard armadillo-like shells, and the highly
intrusive earwigs my daughter calls pinch bugs. There are also numerous types of
insect larvae busily at work.
A person could spend their entire life
trying to understand the ecology of a single handful of humus-rich topsoil. For a
century now, numerous soil biologists have been doing just that and still the job
is not finished. Since gardeners, much less ordinary people, are rarely interested
in observing and naming the tiny animals of the soil, especially are we disinterested
in those who do no damage to our crops, soil animals are usually delineated only
by Latin scientific names. The variations with which soil animals live, eat, digest,
reproduce, attack, and defend themselves fills whole sections of academic science
libraries.
During the writing of this book I became
quite immersed in this subject and read far more deeply into soil biology and microbiology
than I thought I ever would. Even though this area of knowledge has amused me, I
doubt it will entertain most of you. If it does, I recommend that you first consult
specialist source materials listed in the bibliography for an introduction to a huge
universe of literature.
I will not make you yawn by mentioning
long, unfamiliar Latin names. I will not astonish you with descriptions of complex
reproductive methods and beautiful survival strategies. Gardeners do not really need
this information. But managing the earth so that soil animals are helped and not
destroyed is essential to good gardening. And there are a few qualities of soil animals
that are found in almost all of them. If we are aware of the general characteristics
of soil animals we can evaluate our composting and gardening practices by their effect
on these minuscule creatures.
Compared to the atmosphere, soil is
a place where temperature fluctuations are small and slow. Consequently, soil animals
are generally intolerant to sudden temperature changes and may not function well
over a very wide range. That's why leaving bare earth exposed to the hot summer sun
often retards plant growth and why many thoughtful gardeners either put down a thin
mulch in summer or try to rapidly establish a cooling leaf canopy to shade raised
beds. Except for a few microorganisms, soil animals breathe oxygen just like other
living things and so are dependent on an adequate air supply. Where soil is airless
due to compaction, poor drainage, or large proportions of very fine clay, soil animals
are few in number.
The soil environment is generally quite
moist; even when the soil seems a little dryish the relative humidity of the soil
air usually approaches 100 percent. Soil animals consequently have not developed
the ability to conserve their body moisture and are speedily killed by dry conditions.
When faced with desiccation they retreat deeper into the soil if there is oxygen
and pore spaces large enough to move about. So we see another reason why a thin mulch
that preserves surface moisture can greatly increase the beneficial population of
soil animals. Some single-cell animals and roundworms are capable of surviving stress
by encysting themselves, forming a little "seed" that preserves their genetic
material and enough food to reactivate it, coming back to life when conditions improve.
These cysts may endure long periods of severe freezing and sometimes temperatures
of over 150° F.
Inhabitants of leaf litter reside close
to the surface and so must be able to experience exposure to dryer air and light
for short times without damage. The larger litter livers are called primary decomposers.
They spend most of their time chewing on the thick reserve of moist leaves contacting
the forest floor. Primary decomposers are unable to digest the entire leaf. They
extract only the easily assimilable substances from their food: proteins, sugars
and other simple carbohydrates and fats. Cellulose and lignin are the two substances
that make up the hard, permanent, and woody parts of plants; these materials cannot
be digested by most soil animals. Interestingly, just like in a cow's rumen, there
are a few larvae whose digestive tract contains cellulose-decomposing bacteria but
these larvae have little overall effect.
After the primary consumers are finished
the leaves have been mechanically disintegrated and thoroughly moistened, worked
over, chewed to tiny pieces and converted into minuscule bits of moist excrement
still containing active digestive enzymes. Many of the bacteria and fungi that were
present on the leaf surfaces have passed through this initial digestion process alive
or as spores waiting and ready to activate. In this sense, the excrement of the primary
decomposers is not very different than manure from large vegetarian mammals like
cows and sheep although it is in much smaller pieces.
Digestive wastes of primary decomposers
are thoroughly inoculated with microorganisms that can consume cellulose and lignin.
Even though it looks like humus, it has not yet fully decomposed. It does have a
water-retentive, granular structure that facilitates the presence of air and moisture
throughout the mass creating perfect conditions for microbial digestion to proceed.
This excrement is also the food for
a diverse group of nearly microscopic soil animals called secondary decomposers.
These are incapable of eating anything that has not already been predigested by the
primary decomposers. The combination of microbes and the digestive enzymes of the
primary and secondary decomposers breaks down resistant cellulose and to some degree,
even lignins. The result is a considerable amount of secondary decomposition excrement
having a much finer crumb structure than what was left by the primary decomposers.
It is closer to being humus but is still not quite finished.
Now comes the final stage in humus
formation. Numerous species of earthworms eat their way through the soil, taking
in a mixture of earth, microbes, and the excrement of soil animals. All of these
substances are mixed together, ground-up, and chemically recombined in the worm's
highly active and acidic gut. Organic substances chemically unite with soil to form
clay/humus complexes that are quite resistant to further decomposition and have an
extraordinarily high ability to hold and release the very nutrients and water that
feed plants. Earthworm casts (excrement) are mechanically very stable and help create
a durable soil structure that remains open and friable, something gardeners and farmers
call good tilth or good crumb. Earthworms are so vitally important to soil fertility
and additionally useful as agents of compost making that an entire section of this
book will consider them in great detail.
Let's underline a composting lesson
to be drawn from the forest floor. In nature, humus formation goes on in the presence
of air and moisture. The agents of its formation are soil animals ranging in complexity
from microorganisms through insects working together in a complex ecology. These
same organisms work our compost piles and help us change crude vegetation into humus
or something close to humus. So, when we make compost we need to make sure that there
is sufficient air and moisture.
Decomposition is actually a process
of repeated digestions as organic matter passes and repasses through the intestinal
tracts of soil animals numerous times or is attacked by the digestive enzymes secreted
by microorganisms. At each stage the vegetation and decomposition products of that
vegetation are thoroughly mixed with animal digestive enzymes. Soil biologists have
observed that where soil conditions are hostile to soil animals, such as in compacted
fine clay soils that exclude air, organic matter is decomposed exclusively by microorganisms.
Under those conditions virtually no decomposition-resistant humus/clay complexes
form; almost everything is consumed by the bacterial community as fuel. And the non-productive
soil is virtually devoid of organic matter.
Sir Albert Howard has been called the
'father of modern composting.' His first composting book (1931) The Waste Products
of Agriculture, stressed the vital importance of animal digestive enzymes from
fresh cow manure in making compost. When he experimented with making compost without
manure the results were less than ideal. Most gardeners cannot obtain fresh manure
but fortunately soil animals will supply similar digestive enzymes. Later on when
we review Howard's Indore composting method we will see how brilliantly Sir Albert
understood natural decomposition and mimicked it in a composting method that resulted
in a very superior product.
At this point I suggest another definition
for humus. Humus is the excrement of soil animals, primarily earthworms, but including
that of some other species that, like earthworms, are capable of combining partially
decomposed organic matter and the excrement of other soil animals with clay to create
stable soil crumbs resistant to further decomposition or consumption.
Nutrients in the Compost Pile
Some types of leaves rot much faster
on the forest floor than others. Analyzing why this happens reveals a great deal
about how to make compost piles decompose more effectively.
Leaves from leguminous (in the same
botanical family as beans and peas) trees such as acacia, carob, and alder usually
become humus within a year. So do some others like ash, cherry, and elm. More resistant
types take two years; these include oak, birch, beech, and maple. Poplar leaves,
and pine, Douglas fir, and larch needles are very slow to decompose and may take
three years or longer. Some of these differences are due to variations in lignin
content which is highly resistant to decomposition, but speed of decomposition is
mainly influenced by the amount of protein and mineral nutrients contained in the
leaf.
Plants are composed mainly of carbohydrates
like cellulose, sugar, and lignin. The element carbon is by far the greater part
of carbohydrates [carbo(n)hydr(ogen)ates] by weight. Plants can readily manufacture
carbohydrates in large quantities because carbon and hydrogen are derived from air
(C02) and water (H2O), both substances being available to plants in almost unlimited quantities.
Sugar, manufactured by photosynthesis,
is the simplest and most vital carbohydrate. Sugar is "burned" in all plant
cells as the primary fuel powering all living activities. Extra sugar can be more
compactly stored after being converted into starches, which are long strings of sugar
molecules linked together. Plants often have starch-filled stems, roots, or tubers;
they also make enzymes capable of quickly converting this starch back into sugar
upon demand. We homebrewers and bakers make practical use of a similar enzyme process
to change starches stored in grains back to sugar that yeasts can change into alcohol.
C/N of Various Tree Leaves/Needles
| False acacia |
14:1 |
Fir |
48:1 |
| Black alder |
15:1 |
Birch |
50:1 |
| Gray alder |
19:1 |
Beech |
51:1 |
| Ash |
21:1 |
Maple |
52:1 |
| Birds's eye cherry |
22:1 |
Red oak |
53:1 |
| Hornbeam |
23:1 |
Poplar |
63:1 |
| Elm |
28:1 |
Pine |
66:1 |
| Lime |
37:1 |
Douglas fir |
77:1 |
| Oak |
47:1 |
Larch |
113:1 |
The protein content of tree leaves is very similar
to their ratio of carbon (C) compared to nitrogen (N)
Sometimes plants store food in the
form of oil, the most concentrated biological energy source. Oil is also constructed
from sugar and is usually found in seeds. Plants also build structural materials
like stem, cell walls, and other woody parts from sugars converted into cellulose,
a substance similar to starch. Very strong structures are constructed with lignins,
a material like cellulose but much more durable. Cellulose and lignins are permanent.
They cannot be converted back into sugar by plant enzymes. Nor can most animals or
bacteria digest them.
Certain fungi can digest cellulose
and lignin, as can the symbiotic bacteria inhabiting a cow's rumen. In this respect
the cow is a very clever animal running a cellulose digestion factory in the first
and largest of its several stomachs. There, it cultures bacteria that eat cellulose;
then the cow digests the bacteria as they pass out of one stomach and into another.
Plants also construct proteins, the
vital stuff of life itself. Proteins are mainly found in those parts of the plant
involved with reproduction and photosynthesis. Protein molecules differ from starches
and sugars in that they are larger and amazingly more complex. Most significantly,
while carbohydrates are mainly carbon and hydrogen, proteins contain large amounts
of nitrogen and numerous other mineral nutrients.
Proteins are scarce in nature. Plants
can make them only in proportion to the amount of the nutrient, nitrogen, that they
take up from the soil. Most soils are very poorly endowed with nitrogen. If nitrate-poor,
nutrient-poor soil is well-watered there may be lush vegetation but the plants will
contain little protein and can support few animals. But where there are high levels
of nutrients in the soil there will be large numbers of animals, even if the land
is poorly watered and grows only scrubby grasses--verdant forests usually feed only
a few shy deer while the short grass semi-desert prairies once supported huge herds
of grazing animals.
Ironically, just as it is with carbon,
there is no absolute shortage of nitrogen on Earth. The atmosphere is nearly 80 percent
nitrogen. But in the form of gas, atmospheric nitrogen is completely useless to plants
or animals. It must first be combined chemically into forms plants can use, such
as nitrate (NO3) or ammonia (NH3). These chemicals are referred to as "fixed
nitrogen."
Nitrogen gas strongly resists combining
with other elements. Chemical factories fix nitrogen only at very high temperatures
and pressures and in the presence of exotic catalysts like platinum or by exposing
nitrogen gas to powerful electric sparks. Lightning flashes can similarly fix small
amounts of nitrogen that fall to earth dissolved in rain.
And certain soil-dwelling microorganisms
are able to fix atmospheric nitrogen. But these are abundant only where the earth
is rich in humus and minerals, especially calcium. So in a soil body where large
quantities of fixed nitrogen are naturally present, the soil will also be well-endowed
with a good supply of mineral nutrients.
Most of the world's supply of combined
nitrogen is biologically fixed at normal temperatures and standard atmospheric pressure
by soil microorganisms. We call the ones that live freely in soil "azobacteria"
and the ones that associate themselves with the roots of legumes "rhizobia."
Blue-green algae of the type that thrive in rice paddies also manufacture nitrate
nitrogen. We really don't know how bacteria accomplish this but the nitrogen they
"fix" is the basis of most proteins on earth.
All microorganisms, including nitrogen-fixing
bacteria, build their bodies from the very same elements that plants use for growth.
Where these mineral elements are abundant in soil, the entire soil body is more alive
and carries much more biomass at all levels from bacteria through insects, plants,
and even mammals.
Should any of these vital nutrient
substances be in short supply, all biomass and plant growth will decrease to the
level permitted by the amount available, even though there is an overabundance of
all the rest. The name for this phenomena is the "Law of Limiting Factors."
The concept of limits was first formulated by a scientist, Justus von Liebig, in
the middle of the last century. Although Liebig's name is not popular with organic
gardeners and farmers because misconceptions of his ideas have led to the widespread
use of chemical fertilizers, Liebig's theory of limits is still good science.
Liebig suggested imagining a barrel being
filled with water as a metaphor for plant growth: the amount of water held in the
barrel being the amount of growth. Each stave represents one of the factors or requirements
plants need in order to grow such as light, water, oxygen, nitrogen, phosphorus,
copper, boron, etc. Lowering any one stave of the barrel, no matter which one, lessens
the amount of water that can be held and thus growth is reduced to the level of the
most limited growth factor.
For example, one essential plant protein
is called chlorophyll, the green pigment found in leaves that makes sugar through
photosynthesis. Chlorophyll is a protein containing significant amounts of magnesium.
Obviously, the plant's ability to grow is limited by its ability to find enough fixed
nitrogen and also magnesium to make this protein.
Animals of all sizes from elephants
to single cell microorganisms are primarily composed of protein. But the greatest
portion of plant material is not protein, it is carbohydrates in one form or another.
Eating enough carbohydrates to supply their energy requirements is rarely the survival
problem faced by animals; finding enough protein (and other vital nutrients) in their
food supply to grow and reproduce is what limits their population. The numbers and
health of grazing animals is limited by the protein and other nutrient content of
the grasses they are eating, similarly the numbers and health of primary decomposers
living on the forest floor is limited by the nutrient content of their food. And
so is the rate of decomposition. And so too is this true in the compost pile.
The protein content of vegetation is
very similar to its ratio of carbon (C) compared to nitrogen (N). Quick laboratory
analysis of protein content is not done by measuring actual protein itself but by
measuring the amount of combined nitrogen the protein gives off while decomposing.
Acacia, alder, and leaves of other proteinaceous legumes such as locust, mesquite,
scotch broom, vetch, alfalfa, beans, and peas have low C/N ratios because legume
roots uniquely can shelter clusters of nitrogen-fixing rhizobia. These microorganisms
can supply all the nitrate nitrogen fast-growing legumes can use if the soil is also
well endowed with other mineral nutrients rhizobia need, especially calcium and phosphorus.
Most other plant families are entirely dependent on nitrate supplies presented to
them by the soil. Consequently, those regions or locations with soils deficient in
mineral nutrients tend to grow coniferous forests while richer soils support forests
with more protein in their leaves. There may also be climatic conditions that favor
conifers over deciduous trees, regardless of soil fertility.
It is generally true that organic matter
with a high ratio of carbon to nitrogen also will have a high ratio of carbon to
other minerals. And low C/N materials will contain much larger amounts of other vital
mineral nutrients. When we make compost from a wide variety of materials there are
probably enough quantity and variety of nutrients in the plant residues to form large
populations of humus-forming soil animals and microorganisms. However, when making
compost primarily with high C/N stuff we need to blend in other substances containing
sufficient fixed nitrogen and other vital nutrient minerals. Otherwise, the decomposition
process will take a very long time because large numbers of decomposing organisms
will not be able to develop.
C/N of Compostable Materials
|
±6:1
|
±12:1
|
±25:1
|
±50:1
|
±100:1
|
| |
|
|
|
|
| Bone Meal |
Vegetables |
Summer grass |
cornstalks (dry) |
Sawdust |
| Meat scraps |
Garden weeds |
Seaweed |
Straw (grain) |
Paper |
| Fish waste |
Alfalfa hay |
Legume hulls |
Hay (low quality) |
Tree bark |
| Rabbit manure |
Horse manure |
Fruit waste |
|
Bagasse |
| Chicken manure |
Sewage sludge |
Hay (top quality) |
|
Grain chaff |
| Pig manure |
Silage |
|
|
Corn cobs |
| Seed meal |
Cow manure |
|
|
Cotton mill waste |
The lists in this table of carbon/nitrogen
ratios are broken out as general ranges of C/N. It has long been an unintelligent
practice of garden-level books to state "precise" C/N ratios for materials.
One substance will be "23:1" while another will be "25:1." Such
pseudoscience is not only inaccurate but it leads readers into similar misunderstandings
about other such lists, like nitrogen contents, or composition breakdowns of organic
manures, or other organic soil amendments. Especially misleading are those tables
in the back of many health and nutrition books spelling out the "exact"
nutrient contents of foods. There is an old saying about this: 'There are lies, then
there are damned lies, and then, there are statistics. The worse lies of all can
be statistics.'
The composition of plant materials
is very dependent on the level and nature of the soil fertility that produced them.
The nutrition present in two plants of the same species, even in two samples of the
exact same variety of vegetable raised from the same packet of seed can vary enormously
depending on where the plants were grown. William Albrecht, chairman of the Soil
Department at the University of Missouri during the 1930s, was, to the best of my
knowledge, the first mainstream scientist to thoroughly explore the differences in
the nutritional qualities of plants and to identify specific aspects of soil fertility
as the reason why one plant can be much more nutritious than another and why animals
can be so much healthier on one farm compared to another. By implication, Albrecht
also meant to show the reason why one nation of people can be much less healthy than
another. Because his holistic outlook ran counter to powerful vested interests of
his era, Albrecht was professionally scorned and ultimately left the university community,
spending the rest of his life educating the general public, especially farmers and
health care professionals.
Summarized in one paragraph, Albrecht
showed that within a single species or variety, plant protein levels vary 25 percent
or more depending on soil fertility, while a plant's content of vital nutrients like
calcium, magnesium, and phosphorus can simultaneously move up or down as much as
300 percent, usually corresponding to similar changes in its protein level. Albrecht
also discovered how to manage soil in order to produce highly nutritious food. Chapter
Eight has a lot more praise for Dr. Albrecht. There I explore this interesting aspect
of gardening in more detail because how we make and use organic matter has a great
deal to do with the resulting nutritional quality of the food we grow.
Imagine trying to make compost from
deficient materials such as a heap of pure, moist sawdust. What happens? Very little
and very, very slowly. Trees locate most of their nutrient accumulation in their
leaves to make protein for photosynthesis. A small amount goes into making bark.
Wood itself is virtually pure cellulose, derived from air and water. If, when we
farmed trees, we removed only the wood and left the leaves and bark on the site,
we would be removing next to nothing from the soil. If the sawdust comes from a lumber
mill, as opposed to a cabinet shop, it may also contain some bark and consequently
small amounts of other essential nutrients.
Thoroughly moistened and heaped up,
a sawdust pile would not heat up, only a few primary decomposers would take up residence.
A person could wait five years for compost to form from pure moist sawdust and still
not much would happen. Perhaps that's why the words "compost" and "compot"
as the British mean it, are connected. In England, a compot is a slightly fermented
mixture of many things like fruits. If we mixed the sawdust with other materials
having a very low C/N, then it would decompose, along with the other items.
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