HOW MUCH COMPOST
SHOULD WE USE?
EHRENFRIED E. PFEIFFER
The question
of the rate of application per acre is one that is frequently asked. More recently, another has come up: Can we use too much? Here is our advice. Make all the compost you can in your garden
and on your farm, using all available wastes, and it will never be too
much. In fact, in many cases it will not
be enough. If you have to buy compost,
manure or fertilizers made from organic wastes, buy with reason and with
knowledge, not at random. The term compost
as used in this article includes well-rotted manure – not fresh manure.
Maximum applications of 150
tons per acre have been seen, but on the average 5 to 20 tons per acre are more
usual. Of dehydrated, skillfully
manufactured and concentrated composts, as little as one ton per acre may be
sufficient. The range is wide so common
sense and some basic knowledge are necessary.
When using inorganic fertilizers one is guided by their formulas and the
apparent needs of the plants to be fertilized.
While the chemical formula of the inorganic fertlilizer gives a lead as
to its rate of application, the chemical formula of a compost does not entirely
answer this question, although it can help in determining its usefulness. The customary NPK (nitrogen, phosphate,
potash) analysis indicates only a small part of the total value of composts.
The chemical farmer and
gardener knows the NPK and lime requirements of his crops. More recently he also considers (or should
consider) magnesium and a long list of trace minerals. Only now is he beginning to appreciate the
value of organic matter. He knows the
behavior of heavy clay soils and light sandy soils. In practice he applies very little of the
existing information about the availability of minerals. It is true that he buys available fertilizer
elements. State laws prescribe the use
of formulas on fertilizers with regard to soluble inorganic nitrogen such as
sulphate or nitrate of ammonium, and organic nitrogen (urea, for instance);
available phosphates (such as superphospate) as against total or unavailable
phosphates (rock phosphates, for example); water soluble potash or available
potash, to mention the big three (N P K).
Lime is used in accordance with the degree of acidity of a field or its calcium
deficiency.
Rarely, if ever, does the
farmer or gardener ask: Do these
fertilizers remain available in the soil?
Are they efficiently used or wasted.
In recent years, there has come to light a fact which can be of utmost
importance; mineral plant food elements can be tied down in a soil. Lime can be applied by the ton year after
year but the pasture or hayfield remains acid.
It has been tied down and carried into the deeper layers of the soil
where it cannot be reached by the plant roots.
Actually such fields have been over-limed. In certain soils available phosphates can
become unavailable almost immediately after application. Thus in alkaline soils they may become
altogether unavailable right away, and in acid soils only a fraction of the
phosphate may remain useful for the immediate crop, usually between 2 and 10
per cent, at best 20 per cent. The bulk
of the phosphate fertilizer is tied down, has become unavailable. Lucky the farmer whose soil conditions are
such that the phosphate fertilizer, due to microlife and cultivation, can be
made available in successive years.
Unlucky the farmer whose soil stores the phosphate or transports it to
lower levels inaccessible to roots or even lets it wash out (chemical erosion
vertically downward). Such soils remind
one of the old story of a thirsty horse who is tied to a fountain, but with so
short a halter that he cannot reach the water.
The fountain can be ever running, the farmer will buy more and more; in
fact, he finds that he needs more and more every year to hold his yield level. The term “water soluble potash”, prescribed
by some State laws on the fertilizer bag, is especially deceptive. Water soluble means what it says. It is that part of potash which runs away
with the water (rain or irrigation). It
is also most easily absorbed by plants, too easily, in fact, and then leads to
luxury consumption causing disturbances in the metabolism of the plants and the
animals which eat them. Besides all this
there are the problems of the inter-relationship of trace mineral availability
or unavailability and the other fertilizer elements. One example is the adverse relationship
between boron and lime.
Composts behave differently
and cannot be judged entirely by their NPK formula. Nitrogen in compost is mostly organic
nitrogen. Much less nitrates are present
and very little ammonia should be present.
Phosphates and potash are also present, but in forms which do not show
up through the prescribed analytical procedures for determining availability or
water solubility. At best, following
customary analytical methods one can determine the total amount of nitrogen,
phosphate and potash. But these methods
do not take into account the fact that – due to the microlife in the soil
and in the compost – these compounds are slowly gradually made available in
soil when compost is applied.
Experience has shown that
low nitrogen formulas (1 to 2%) in compost produced as good results as the
application of high nitrogen fertilizer formulas (6-16%) with one important
difference. Highly soluble fertilizer
elements produce a rapid but not lasting effect while composts produce a slower
but longer lasting effect. The effects
of highly soluble and available fertilizer elements make the best showing
during the first tree to six weeks after application. The elements in composts last for three to
six months with a steady release, and if the soil is rich in organic matter,
further beneficial effects can be seen in the second and even in the third
year.
Now we come to the most
important question. Not all composts are
alike, either in formula or in behavior.
Here the greatest mistakes have been made in the past by using composts
indiscriminately under the far too general heading “compost” or “the organic
method”. Of fertilizers there are many
brands and formulas. There are also many
different formulas of compost, maybe even many more than of fertilizers. A grading of composts is absolutely necessary
if one wants to use them efficiently.
But the intrinsic processes in a living compost and in soils should
also be understood in order to arrive at maximum effects. The different types of possible composts
must therefore be considered.
We will begin with the organic
matter content of compost. It is
incorrect, as one reads here and there, to say that a compost contains 100%
organic matter. It is correct to say
that it has been made from organic wastes such as plant (garden) refuse,
leaves, garbage, sawdust, animal wastes, manure, etc. These materials are of organic origin because
they derive from things which at one time were living organisms. If plastics are used they may be products of
organic compounds. But most of these
source materials also contain inorganic minerals. A living plant contains 2 to 10% inorganic
compounds which upon combustion show up as ashes. Organic materials in strictly chemical terms
are combustible and derive from complicated compounds of the chemistry of
carbon, nitrogen, hydrogen, and oxygen, sometimes combined with other elements
such as sulphur and phosphates as in proteins and their breakdown products; or
carbon compounds like sugar, cellulose, hemicellulose; or combinations with
calcium, magnesium and other mineral elements. A compost is a breakdown product
of all these materials. Microorganisms
have used part or all of these breakdown products and ‘digested’ them, building
up new compounds which in turn again break down. It is of the utmost significance for the
fertilizer value of composts to what degree these breakdowns, new syntheses,
secondary breakdowns, have taken place.
The final, end products of all breakdown processes are: carbon dioxide,
simple nitrogen compounds such as N2, NO2 , NO3
, NH3 , and water; all of which can be lost in one way or another.
Simple mineral compounds result such as calcium, magnesium, other nitrates,
ammonia salts, carbonates as well as silicates and aluminates as they may
happen to be present in the source materials. The organic matter content of a
compost therefore can vary greatly.
Average farm and garden made
composts contain a sizable amount of earth.
The organic matter content is therefore low. In fact most of these
composts range between 12 and 20% organic matter content, a percentage of 20 to
30 is rarely if ever found. Many piles,
especially if they are earthy, old and well-rotted are nearer the 12% level and
piles with less, even as low as 6 to 9%, have been frequently encountered in
our analytical work. These are still
called compost because of their origin and the way in which they have been
treated, but actually they have become soil – a rich soil, though, rich in
organic matter. Here a mineralization
process has taken place and most of the carbon has vanished in the form of
carbon dioxide. It is evident that such
mineralized composts behave entirely differently when applied to soils than
others with a high organic matter content.
It is an illusion for the gardener to think that he can appreciably
increase the organic matter in his soils by using low organic matter composts. While they still will be of benefit to the
soil structure, improving soil particle agglomeration or aggregation, their
main value is in their mineral content whatever it may be. Of these low organic matter composts a
considerable amount has to be given per acre if any apparent results are to be
obtained.
RULE I: Of earthy, well-rotted, low organic matter composts
10 to 20 tons per acre may be used, or ˝ to 1 lb. per square foot, or 500 to
1000 lbs. per 1000 square feet. No harm
can be done at such rates. However, the
term organic matter only tells us the amount of combustible compounds present
but not the degree of breakdown. Crude
compost may contain the same amount of organic matter as a well-digested
material such as humus. The effect
of a raw compost upon soil is quite different from that of a humified
compost. It is the skillful and
experienced compost manufacturer’s aim to produce a compost with a high organic
matter content in a well broken-down state (humified), but not in an extreme
state of mineralization. So-called
stabilized products of simply broken-down crude organic matter are again
entirely different products, even though their formulas may give the same NPK
percentage as others. Such products
hardly meet the definition compost.
Higher rates of application than those given in Rule I are not desirable
for many reasons, one of these being the increased packing and hardening of the
soil due to hauling so many truck loads over the field, not to speak of the
cost of the spreading operation.
A word must now be said
about the moisture content. A
homemade garden or farm compost is usually wet and in this state has a moisture
content of about 50%; or it may be dry to the touch, and then the moisture will
run from 20 to 30%. If it is dusty, it
will probably contain less than 15% moisture.
A yardstick to help in estimating moisture content and hints on how to
acquire it were outlined in an article in BIO-DYNAMICS some time ago. (1) It
should be realized that more of a material containing half of its weight in
water must be used than of another containing only a quarter of its weight in
water. The above given rate of 10
tons/acre applies to fairly dry but not dusty composts, and the rate of 20
tons/acre applies to wet or rather moist composts. A dryer compost contains a higher percentage
of minerals than a wet one, one might say that it is a ‘stronger solution’. Analyses of composts should, therefore, not
only give the organic matter and mineral content, but also the moisture content. For example, one can calculate the absolute
content on a dry basis, but this is not the percentage that is applied in
practice.
As far as crop growth and
yield are concerned the nitrogen content is certainly decisive. We should know the nitrogen content. However,
reference must again be made to the moisture content. We will fare much better if we know not only
the percentage of nitrogen but also how many pounds per acre of nitrogen
we are giving at the given rate of application.
Most homemade garden and farm composts, manure from horses, cattle, and
hogs, have a total nitrogen content of 0.5 to 0.7% at a moisture of 50% and
more. Cattle manures have a moisture
content of 80%. Poultry manure is the
exception and can contain as much as 1.5% total nitrogen at high moisture
levels. On a dry basis, the total nitrogen
content of all of these will be higher.
Dry compost will run from 1 to 2%; dry cattle (steer) manure may have as
much as 2%, poultry manure 2.5 to 3% nitrogen.
Compost or manure of 1%
nitrogen contains 20 lbs. of nitrogen per ton no matter what the moisture
content is. If one ton of a 1% nitrogen compost is applied to an acre you are
applying 20 lbs. of nitrogen. If ten
tons are spread you will be giving 200 lbs. per acre. 0.5% nitrogen in a manure or home garden
compost means that, at the rate of 10 tons/acre, 100 lbs. of nitrogen are
applied, or at the rate of 20 tons/acre 200 lbs. of nitrogen are applied.
Two hundred pounds of
nitrogen is the upper limit for most crops.
Many corps require less, for instance 60, 80, or 120 lbs. It is evident that much less of a high
nitrogen, low moisture compost need be applied per acre than the
above-mentioned figure of 10 tons. In
fact we have seen good results with the B.D. Starter produced compost when only
1 ton/acre was used. This compost was,
of course, dry.
An insufficiently rotted,
rather raw compost of low nitrogen content should not be used. Its further decomposition in the soil arrests
all nitrogen fixation for a considerable length of time, namely until the raw
materials are completely digested. Such
composts have a depressing effect upon the nitrogen level in soils similar to
the effect of green manuring. Their
value begins to show up only after many months, often only during the second
year, as is the case when one uses fresh manure. Applications of these materials should be
made in fall, never in spring just before seeding or planting. The same holds true for sheet composting of
organic wastes and trash, and for partly rotted straw and sawdust compost. Well-rotted composts can be applied at any
time although a moist soil is a better recipient than a dry one. Desert remains desert as long as there is no
moisture.
Completely mineralized
composts are the other extreme and cannot be called ‘organic fertilizers’. In completely mineralized composts, however,
the minerals are usually in a high available form while in partly-rotted, raw
composts they are usually unavailable.
From all these facts it
appears that the proper degree of breakdown in a compost is important in
determining the effective amounts to apply. If a compost with 2 to 3% nitrogen,
but not well decomposed (i.e. more or less raw) is applied most of the nitrogen
is lost in the soil. One would fare much
better with the 1% nitrogen of a well-rotted compost. In the latter, the nitrogen will be slowly
and steadily made available to plant roots and the microlife in soil. It should always be remembered that we
feed the microlife first and only secondarily the plant root. It is the microlife in soil which turns the
minerals into forms which the plant roots can take up, or not, as the case may
be. (2) (3).
An ammonia odor in compost
or manure indicates the presence of free ammonia. Since ammonia has a strong smell its presence
is not always an indication of a high ammonia, i.e. nitrogen content. Fresh manure, after a few days, can really
stink of ammonia and yet contain only 0.5% nitrogen. The ammonia odor, however, indicates that the
ammonia is free, that it can easily be lost or washed out and only that much is
used as the plant roots can absorb at once.
The balance is readily lost unless there is nitrification or other
fixation process going on in the soil.
When the manufacture of compost from garbage was started and the product
sold to farmers, we were especially proud of the fact that the compost had an
earthy, agreeable smell. Some of the
salesmen came back and reported that we should give it a stronger odor because
the farmers said that it didn’t have ‘that strong fragrance of manure’. We thought that in the interest of nitrogen
preservation and effectiveness it would be better to perfume the compost than
to permit a decomposition with a strong ammonia smell. Without nitrogen fixation ammoniac composts
have an immediate, but not lasting effect on plant growth. The plants may grow too lush and go to seed
too early (under drought conditions), or set weak seed (under wet conditions),
for most of the ammonia nitrogen is lost long before the plants mature. Too much of an easily available form of
nitrogen may even lead to burns on plants as can be seen when fresh poultry
manure or too much concentrated urea, is applied to lawns.
Phosphates and potash are
present in composts in both organic and inorganic forms, and are made available
by soil bacteria and their enzymes no matter whether the chemical laboratory
tests show them to be present in available or water soluble form or not. It is, therefore, in the interest of the
compost producer as well as the compost user to create such conditions that an
active microlife can be utilized. This
is only possible in the presence of moisture, organic matter (the more the
better), and aeration, that is, proper cultivation. The release of these elements in the soil is
also slow and steady. In addition, in
soils which have been treated intensively with fertilizers in the past, the increased
microlife will bring tied down phosphates and potash back into circulation. The low P and K in composts (which usually
range from 0.5 to 1.5%, in the best products up to 2%) are no obstacle since
maximum effectiveness and availability are obtained. Again it should be remembered that the
application rate for composts is quite different from that recommended for
concentrated inorganic fertilizers. If 1
ton of compost at 1% P or K is applied to an acre this means that 20 lbs. of
the corresponding element are given. Ten
tons of the same compost contain 200 lbs., which in most cases is
sufficient. Dry B.D. Compost Starter
treated composts are actually concentrates, and the 2% phosphates or
potash in them provide 40 lbs. of P or K per acre at the rate of 1 ton/acre –
all available in due time, and no losses or tieing down are encountered.
It is our firm opinion,
based on laboratory and field tests as well as on many years of practical
application (4), that composting can be done very well along scientific,
analytical lines. The first step is to
know your compost and what it contains.
You ought also to know your soils and the crop demands. Finally you ought to know the crop rotation
and take into account the beneficial influences of legumes and green manuring.
A soil analysis will tell
which elements are abundant and which are lacking or deficient. But chemical information about your soil is
not the only important thing. It is the
physical structure of the soil and the climate or weather which play a decisive
role in the efficient and effective use of composts. Light, sandy soils can absorb large
amounts of compost until they build up humus – organic reserves. Once a 2% organic matter level is reached
they will make full use of compost as fertilizer. Below a 1.5% organic matter level part or all
of the compost applied will be used either for soil building (when the
compounds in the compost become available slowly), or as fertilizer (when the
compounds are readily and quickly available ones). Soils below the 1.5% organic matter level
have no reserves and live from day to day.
Medium-heavy clay soils with
better than 2% organic matter are the ideal soils. Very heavy clay or loamy soils react
sluggishly and large amounts of manure or compost have to be applied before you
can see any results at all. However,
these amounts are not lost, they are stored.
It is more important to aerate and drain heavy soils according to the
best knowledge of agriculture to make the best and most effective use of
composts. These in turn aid in loosening
up heavy soils and improve the structure.
Once the structure is improved the full effectiveness of composts as
fertilizers will be apparent. In a
garden raised beds, for truck and field crops furrow cultivation, will greatly
improve such heavy soils.
The higher the organic
matter level, the better the soil structure, the smaller the amount of compost
which is needed. Good drainage is a must
for efficient compost use. In wet, heavy
soils no compost should be buried deep.
The climatic conditions and weather also have a bearing on the rate of
compost application. The general rule is
that heat and drought destroy organic matter faster than cool and rainy
climates. In hot, dry climates, as
well as on light and heavy soils, it is more efficient to use smaller amounts
and apply them more often. This
practice is recommended, by the way, for all difficult soils. In such cases, yearly applications are
preferable, while on well-maintained soils one heavier application once in a
while (once in a four-year crop rotation, for instance) is usually more
practicable.
Last but not least, the crop
demands and crop rotation need to be considered. A general differentiation should be made between
plants with high, moderate or low nutritional requirements. In using compost
where we have a natural balance in the soil one can take a chance and think in
terms of tons per acre, even though the NPK details are not know. However, to this writer, the full application
of all possible information is always preferable. A commercial farmer should use all the
information; the home gardener can risk getting away with a general
application.
Heavy nutritional demands on soil are made by the
following: Corn, tomatoes, potatoes,
beets, peppers, cucumbers, spinach, chard, cabbage, cauliflower, endive,
escarole, chicory, celery, squash, pumpkins, okra, rhubarb, sunflowers, roses,
peonies and some other perennial flowers, berries, heavy-bearing fruit trees,
nut trees, avocados, bulbs, lawns.
Plants which make moderate nutritional demands are: Lettuce, carrots,
turnips, early garden beets, Brussels sprouts, kohlrabi, leeks, onions, most
spring flowers, pasture and hay grasses, small grains, in general, shallow-rooting
plants.
Light demands are made, especially in
fertile soils with a high organic matter content, by radishes, most herbs
(medicinal herbs in particular), legumes (peas, beans, clovers, alfalfa and
soybeans if allowed to mature), most summer and fall flowers, buckwheat, tall
pasture and hay grasses with deep growing root systems. To be on the safe side it may be stated (with
a grain of salt) that light feeders turn into heavy feeders on light, sandy
soils and any soil with a low organic matter content. Such soils should be given large quantities
of compost and frequently.
RULE II: Adjust your
compost to the soil and climate.
RULE III: Adjust your compost to the kind of crop you want to
grow.
For poor conditions and
heavy feeders use the maximum amount of 10 tons/arce of a good grade,
wet compost (0.5-0.7-0.5 formula), or less, according to formula, of a dry,
manufactured compost. The compost
manufacturer should be in a position to advise the customer as to the proper
use of his product. Unfortunately, this
is not yet true in the case of most of the products advertised nowadays. These products may have a 2-2-2 formula at
less than 20% moisture, then 2 tons/acre will be enough. Use 2 to 3 tons of 1-1-1 formula at less than
20% moisture. These rates apply only to
products which have an organic matter content better than 20%. Manufactured composts with 12-16% organic
matter, as well as manures, have to be used at the maximum rate.
For good conditions and
moderate feeders use half the rate of maximum demand, for instance, 5 to
7 tons of a moist, homemade compost or 1 to 2 tons in the field. On good soils after a heavy or moderate
feeder, compost can be omitted. On poor
soils a light dressing is advisable.
For light feeders,
minimum amounts can be used; a light sprinkling in a garden, 1 to 2 tons in the
field. On good soils after a heavy or
moderate feeder, compost can be omitted.
On poor soils a light dressing is advisable.
The crop rotation in garden
and field with compost management, on good soils, is best arranged in such a
way that heavy feeders are provided with maximum amounts to be followed by
moderate feeders with half amounts on good soils, to be followed with light
feeders and no compost. On poor and
difficult soils the old power of maximum amounts will probably last into the
second year. Therefore, in such cases,
it is better to use light feeders in the second year of the rotation with a
light application of compost. This is
followed in the third year by moderate feeders with a half rate
application. In the fourth place in the
rotation one can then again place the heavy feeders and apply the full amount
once more. On good soils, in good
condition, either a light or moderate feeder can be grown in the fourth year,
before one returns to the heavy feeders with a full application. These rules should not be adhered to
stubbornly, but used with common sense.
Modifications are always possible.
And we have not included in these possible rotations cover and rest
crops, or rest periods.
Mulching can be done with a
poorer grade of compost which has not become earthy, that is an incompletely
rotted compost. On dry and light soils
and in hot dry climates, it is a must.
Green manuring crops, mown
and top-dressed with a light application of compost, even of a poor compost,
will be twice as effective as those not so treated. The plowed or disked in material will
decompose faster and release its nutrients quicker without tying down nitrogen.
Thus far we have been
dealing with the basic principles of composting and their ordinary practical
application. A further development of
these scientific principles in even more detail will form the basis of future
articles. But on the basis of studies
already made, it is evident that composts can be applied scientifically just
like any other fertilizer, and application rates and the types of compost to be
used figured out for any purpose and requirement.
The two tables printed on
the folded insert will help you in working toward this scientific, economic,
and effective use of your composts. The
first table brings together all the information from the text of this article
which will help you in determining how much of the various types of compost to
use in general practice. With the help
of Table II you can adjust your applications to the individual needs of any
crop.
Our aim is to take the
guesswork and happenstance out of composting and to make it as exact an
agricultural science as possible.
Farmers and gardeners who have done this have fared well over long
periods of years. One observation,
frequently made and confirmed, is quite important in this connection: the usual
application rates especially of low grade composts have more than provided all
the requirements of crops without causing any trouble in regard to soil
structure.
REFERENCES:
(1) HOW MOIST IS MOIST? By E. E.
Pfeiffer,
BIO-DYNAMICS, Fall
& Winter 1953, Vol. XI< Nos. 4 & 5
(2) FEED THE SOIL by F. L. Wynd,
THE SCIENCE MONTHLY, Vol. LXXIV
(3) SEVEN YEARS OF SOIL SURVEY ON A BIODYNAMIC
FARM by E. E. Pfeiffer, BIODYNAMICS,
Summer, 1954,
Vol. XII, No. 3
Reprinted from BIO-DYNAMICS Fall
Issue, 1954
Copyright 1954 by the
Bio-Dynamic
Farming and Gardening Association, Inc.
Reprinted 1984
Table I - Average Compost Application As A Guide to Practice
Table II - Formula and Application Relationship: For Orientation, and for Individual Application of Composts
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