From: london@sunSITE.unc.edu (Larry London)
Subject: Nicely written guide for organic gardeners (from Missouri Coop. Ext)
Date: Mon, 22 Mar 1993 02:08:56 GMT

Organic gardening techniques - Organic matter, fertilization, and
pest control

R. R. Rothenberger and K. Hildahl
Department of Horticulture, College of Agriculture

     The success or failure of the organic approach depends on
how gardeners use and prepare organic matter. Organic matter
improves soil tilth and prevents soil compaction and crusting. It
increases the water-holding ability of the soil and provides a
more favorable soil environment for earthworms and beneficial
microorganisms. It slows erosion, and in later stages of decay,
organic matter releases nitrogen and other nutrients to growing
crops. Carbon dioxide from decaying organic matter brings
minerals of the soil into solution, making them available to
growing plants. Many soils of the world have been ruined, mainly
because they have been depleted of organic matter from prolonged
cultivation without proper soil management.

Sources of organic matter
     Animal manures. Where available, animal manures are
excellent sources of organic matter and nutrients for the soil.
It is best to apply manures after they have been composted and
partially broken down. Fresh manure may be applied directly to
the soil, but this should be done in fall and plowed down so that
there is adequate time for sufficient breakdown and ammonia
release before crops are planted. Those who do not have access to
fresh or composted animal manures may find packaged dried manures
for sale in nurseries and garden stores. Because fresh, composted
manure contains high amounts of water, an equal weight contains
fewer nutrients than dried manure. Also, the fertility of manures
from different sources varies widely. Table 1 gives some average
figures.
     To interpret the table, note that each 100 pounds of fresh
cattle manure contains about 1/2 pound of available nitrogen,
while 100 pounds of dried cattle manure contains about 2 pounds.
Compare these amounts to a common commercial fertilizer such as
10-10-10, which contains 10 pounds of nitrogen per 100 pounds. By
observing the nutrient content of the major constituents of a
fertilizer, a guide to the appropriate rate of application can be
developed (see Table 2).
     Fresh manure should not be used directly among plants or
mixed into soil immediately before seeds or plants are placed in
the garden. Fresh manure produces ammonia as it decomposes.
Ammonia in direct contact with plant roots can cause damage and
must be avoided. Another disadvantage of uncomposted manure is
the introduction of weed seeds into the garden. More detail on
manures is given in Guide 9331, "Animal Manure for Crop
Production."

     Compost. Where manures are not readily available you can
make compost from lawn clippings, leaves and other plant
materials (see Figure 1). Compost is not only convenient, but
also inexpensive. Nutrient content of compost is relatively low,
but its main benefit is the organic matter it adds to improve
soil tilth. For detailed information on compost making, see
Grounds for Gardening Guide 6956, "Making and Using Compost."

     Green manure and fall cover crops. Where the garden area to
be improved is large, or where other forms of organic matter are
not readily available, green manuring is often the most
economical means for soil improvement. Green manuring means
growing a cover crop in your garden and plowing it under, thus
adding organic matter to the soil. The greatest response from
green manuring comes from not using the garden for one season,
while growing a grass or other green manure crop and plowing it
under in early fall.
     Another method is to seed a green manure crop in the fall
and turn it under with a plow or large tiller in early spring.
With this method, you can continue to use your garden normally,
while gradually building up the soil.
     Generally, you should seed a cover crop in September, not
later than October 1. The cover crop protects the garden from
erosion during the winter. Plow under the cover crop when it is 6
to 8 inches tall. If it grows taller, mow it down before plowing.
     Annual ryegrass is one of the most satisfactory plants for
green manuring or covering. Seed it at 1 to 2 pounds per 1,000
square feet of garden space. Seed rye or wheat at 3 to 4 pounds
per 1,000 square feet. Thorough incorporation into the soil is
important in early spring to prevent regrowth and weediness from
these grasses. Wait at least two weeks before planting.

     Sawdust. In some areas where sawdust is readily available,
it provides an excellent source of organic matter for the soil.
You can use sawdust as compost, as mulch or for direct
incorporation into the soil. A normal addition of sawdust would
be about 3 to 4 bushels per 100 square feet of garden area. You
should use only aged sawdust. Sawdust has no appreciable effect
on soil acidity.
     The major problem with adding sawdust is the greater
likelihood of developing nitrogen deficiency. As sawdust breaks
down in the soil, it uses nitrogen, making it unavailable to
plants. Therefore, along with sawdust you need to add materials
that supply nitrogen to keep plants from starving. Apply the
additional nitrogen needed at the time the sawdust is added and
repeat as a side dressing during the growing season. For each
bushel of dry sawdust, apply about 3 pounds dried blood or 1
pound of potassium nitrate or 1/2 pound of ammonium nitrate. You
can also use other materials at rates determined by the
percentage of nitrogen contained. The garden may need later
applications also if plant growth is poor due to lack of
nitrogen.

     Sewage sludge. In some areas, sewage sludge may be available
as a source of organic matter. Two types may be available:
digested sludge and dried, activated sludge.
     Digested sludge is relatively low quality as a fertilizer in
comparison to the other type. Apply and plow in digested sludge
in the early fall. Do not apply digested sludge directly where
you plan to grow a crop the same season, unless it has been
composted. It generally contains from 1 to 3 percent nitrogen.
Sewage sludge can be a highly variable product. Some sources may
contain heavy metal ions and are best not used in the vegetable
garden.
     Dried, activated sludge is made from sewage that has been
separated from coarse solids, inoculated with microorganisms and
aerated. It is filtered, dried in kilns, ground and screened. It
is useful as a fertilizer on lawns and is heat treated, making it
sanitary for garden use. This type of sludge may contain from 5
to 6 percent nitrogen. Apply dried, activated sludge at about 5
to 7 pounds per 100 square feet; apply digested sludge at about 7
to 10 pounds per 100 square feet.
     Never apply untreated or raw sewage to garden soil for any
purpose.

Organic vs. inorganic or
man-made fertilizers

     One of the greatest arguments among gardeners comes in the
area of fertilization. Some prefer totally natural materials;
others are content with man-made materials; many use a
combination of both. In some cases, the selection is based on
economics. Often, the availability of organic materials is
limited when large quantities are needed.
     For plant growth, both forms of fertilizer can be equally
effective. Organisms in the soil break down organic materials to
form inorganic, water-soluble materials identical to those formed
by man. Plants are unable to determine a difference in the
original source of the compounds they absorb. Extra growth often
is a response to better root environments and action of soil
organisms working on the organic matter.
     While some materials, such as manure, add organic matter as
well as fertility, other organic fertilizers are not suppliers of
organic matter. One of the major benefits of organic fertilizers
is that they break down slowly and are less likely to release
nutrients rapidly enough to burn plant roots if used in large
amounts.

Figure 1. Compost is a convenient, inexpensive source of organic
matter.

Many man-made fertilizers are more soluble and can burn plants if
used improperly. Since many organic materials break down slowly,
they supply nutrients to plants for a much longer period of time
without frequent applications. Because they are not quickly
soluble, they are not leached from the soil during heavy rains
and, therefore, are more continuously effective. Some organic
fertilizers also contain micronutrients.
     The availability of nutrients from organic fertilizers
depends on their breakdown by soil organisms, which in turn
depends on weather and soil conditions. Release of nutrients is
much slower when the soil is cool or heavily saturated with
water. Also, breakdown slows during drought unless soil is
irrigated or heavily mulched to keep in soil moisture and keep
temperature more constant. Where you need a quick fertilizer
response, inorganic fertilizers tend to provide it. Many of the
organics have a fertilization lag. Their nutrients are not
available to plants until the organic matter has decomposed.

Sources of organic fertilizers
     Following are some organic fertilizers that supply nutrients
but add little or no organic matter.

     Sources of nitrogen (N). Dried blood contains about 12 to 14
percent nitrogen, and therefore can be considered a nitrogen
fertilizer, although it also contains about 2 percent phosphorus
and 0.5 percent potassium. It may appear either red or black,
depending on the process used to remove water during drying.
Dried blood releases nitrogen relatively fast. General
application is about 2 to 4 pounds dried blood per 100 square
feet of garden area. It leaves an acid reaction in the soil.
Dried blood is sometimes used as a rabbit repellant.
     Hoof and horn meal contains 12 to 14 percent nitrogen as
processed, dried hoofs and horns. Although once commonly used as
a fertilizer, it is now nearly unavailable in most areas.
     Tankage is derived from the dried and ground by-products of
animal slaughter. While often available as a livestock feed, this
same material can be used as a fertilizer. It averages about 6 to
11 percent nitrogen and may contain about 10 percent phosphorus.
Garbage tankage, made from the dried, ground products of
household waste, may also be used, although it is not readily
available.
     Fish meal is the dried, ground, processed material derived
from non-edible fish or fish scraps. As a fertilizer it may
contain from 8 to 10 percent nitrogen, 4 to 9 percent phosphorus
and 2 to 3 percent potassium. As it breaks down, this material
gradually becomes available to plants as a fertilizer. Fish
fertilizers also benefit plants by the addition of many minor and
micronutrients. Fish emulsion is a liquid form often used for
houseplants.

Sources of phosphorus (P205). Bone products, one of the earliest
sources of phosphorus for fertilizing plants, are available in
three forms:
* bone meal (ground bone softened by steam under pressure),
* acidulated bone (ground bone treated with sulfuric acid), and
* ground bone (bones cooked but not steamed).
     Bone meal is the form most often used as a plant food. The
meal from unsteamed bones may contain 20 to 22 percent
phosphorus, while that from steamed bones will contain from 23 to
30 percent P205. Rate of use for soils low in phosphorus is about
2 pounds per 100 square feet. Bone meal is commonly used as a
source of phosphorus in livestock feeds and is generally
available from livestock feed suppliers.
     Rock phosphate is made by grinding a natural rock containing
one or more calcium phosphate minerals. It is used either
directly after grinding or after concentration as a phosphorus
fertilizer. Rock phosphate normally contains between 25 and 30
percent phosphorus. Rock phosphate is more effective in acid
soils and relatively ineffective on alkaline soils due to its low
solubility. It is most useful as an addition in composting manure
and organic materials. Soils low in phosphorus may require ground
rock phosphate at about 2 to 4 pounds per 100 square feet of
garden soil. When applying with manure or compost, use about 2
l/2 pounds per 25 pounds of manure or compost.

Sources of potassium (potash, K20).
     Wood ashes may contain from 4 to 10 percent potassium.
Generally, they average about 5 percent potassium with as much as
23 percent calcium. Because of this, they produce an alkaline
reaction on the soil. Since they go quickly into solution, you
should use them with care. Continued use may raise the pH of the
soil, making it too alkaline unless adjustments are made. Use
wood ashes at a rate of about 2 l/2 pounds per 100 square feet of
garden area. Do not soak ashes in water before application or the
potassium will be lost. Do not apply wood ashes if the soil pH is
over 6.5. Apply ashes at least 3 weeks before planting seeds.
Coal ashes are not beneficial to plant growth.
     Greensand is sometimes recommended as a source of potassium
but is not readily available in many areas. It is a hydrated salt
of iron and potassium silicate and contains about 6 percent
potassium, which is very slowly available to plants.
     Seaweed can be the name for any plant that grows in the
ocean, but the material used for fertilizer is usually made from
brown or red algae. Giant kelp is a seaweed that was harvested
for both fertilizer and explosives during World War I. Kelp
contains 20 to 25 percent potassium chloride, but the seaweed
that is normally available for use as a fertilizer contains from
4 to 13 percent potassium. Although seaweed was once commonly
used as a fertilizer, availability is now relatively limited.

Other organic fertilizer sources.
     A wide variety of other materials may be used as fertilizer.
Some have a more balanced range of nutrients in them, although
often none of the nutrients are in large amounts.
     Cottonseed meal is the residue after the oil is extracted
from cooked cotton seeds. It averages 6 percent nitrogen, 2
percent phosphorus and 1 percent potassium, along with secondary
and micronutrients. Nutrients from cottonseed meal become
available to plants gradually. Cottonseed meal produces an acid
reaction in the soil.
     Soybean meal, as well as cottonseed meal, is mainly used as
an animal feed. However, nonfeed quality meal is sometimes used
as a fertilizer. Its nutrients average about 6 percent nitrogen,
1 percent phosphorus and 2 percent potassium. Its reaction in the
soil is only slightly acid.
     In some localities, other plant materials are available that
may serve as plant nutrients as well as add organic matter. Some
of these include tobacco stems, castor pomace, cocoa shell meal,
sunflower meal and mushroom compost.

Sources of inorganic or
man-made fertilizers
     Those choosing fertilizers from organic sources generally do
not use those that are inorganically made by man. However, since
references and recommendations are often made in terms of
inorganic fertilizers, following are a few of the most common
along with their major nutrient content, so you can make
comparisons.

     Sources of nitrogen (N). Ammonium nitrate is a common
inorganic fertilizer that contains about 33.5 percent nitrogen.
It absorbs moisture from the air when humidity is high, and
therefore, must be stored in tight containers or bags.
     Ammonium sulfate, another common constituent of mixed
fertilizers, contains about 20 percent nitrogen.
     Calcium nitrate, which forms when limestone reacts with
nitric acid and is neutralized with ammonia, contains about 15
percent nitrogen. It has been used as a nitrogen source when
additional calcium may be needed in the soil.
     Sodium nitrate, also called Chile saltpeter, is mined from
natural deposits in Chile but may also be produced synthetically.
It contains about 16 percent nitrogen and 26 percent sodium.
     Urea is an organic compound synthesized by combining carbon
dioxide with ammonia under high temperature and pressure. It
contains no less than 45 percent nitrogen (usually about 46
percent), which is rapidly available to plants. Urea is sometimes
used for foliar fertilizer applications. Its rapid availability
and high nitrogen concentration make careful use important.
     A related product, Urea-formaldehyde fertilizer (also called
Ureaform) has 35 percent or more nitrogen. A large portion of
this nitrogen becomes available to plants gradually. It is much
safer to use than urea, and fewer applications are necessary. It
is a common nitrogen source used in lawn fertilizers.

     Sources of phosphorus (P205). Superphosphate forms when rock
phosphate is treated with either sulfuric acid or phosphoric
acid. The process of production will determine the amount of
phosphorus contained in the finished product and may range from
20 to 50 percent. A common superphosphate analysis is 0-20-0,
while treble superphosphate is 0-450.

     Sources of potassium (K20). Potassium chloride is also known
as muriate of potash. It is made by the action of hydrochloric
(muriatic) acid on potassium-containing materials. It contains
about 60 percent potassium (potash).
     Potassium nitrate is commonly known as saltpeter or nitrate
of potash. Natural deposits occur in some parts of the world and
were once mined extensively. However, most saltpeter is now made
synthetically. It contains a minimum of 12 percent nitrogen and
44 percent potassium. A common analysis is 13-0-44.
     Potassium sulfate is also known as sulfate of potash. It can
be made from a number of potassium-containing materials and
contains about 48 percent potassium.

Adjusting soil acidity
     The acidity of a soil is measured in units called pH. The
proper soil pH is important for the breakdown of organic matter
and the release of nutrients in the soil for plant growth. A soil
pH of 7.0 is neutral, neither acid or alkaline. A pH above 7 is
called a sweet or alkaline soil, while a pH below 7 is known as a
sour or acid soil. Most garden plants grow best in soil with a pH
range from 6.0 to 6.8. Breakdown of organic matter, nutrient
release by microorganisms and availability of most nutrients is
greatest in this pH range.
     A soil test is the only way to accurately determine the pH
of a soil, but plant growth may be an indication of pH problems.
When you have apparently applied adequate fertilizer, but plant
growth is poor, you might suspect improper pH. Ground limestone
is normally used to make acid soils less acid, while sulfur is
used to make alkaline soils more acid.
     Most Missouri soils tend to be acid rather than alkaline,
making the addition of ground limestone more common than the
addition of sulfur. Since the average garden performs best in a
pH range from 6.0 to 6.8, Table 3 suggests sulfur or limestone
required to make a midway change close to 6.5. Remember that
these amounts are approximations, and soil type and conditions
may alter the results. At all times proceed with caution.
Ideally, do not apply more than 1 pound of sulfur or 5 pounds of
limestone per 100 square feet in one application. If larger
amounts are required, split applications between spring and fall
to create a gradual increase or decrease. Work the materials
thoroughly to a depth of 6 or 7 inches.
     If you use wood ashes to reduce acidity, use about two-
thirds the amount recommended for limestone.

Disease control methods
     Plant diseases may seriously stunt or even kill plants. They
may appear as leaf spots, wilts, stunts, rusts or a variety of
other symptoms. Plant diseases may be caused by fungi, bacteria,
viruses, nematodes, or may be a response to environmental
conditions that produce disease-like symptoms. The key to good
disease control is prevention.
     Some, but not all, diseases may require frequent spraying
with traditional chemicals to provide adequate control. Use
cultural procedures to prevent disease infection with or without
spraying to help reduce the seriousness of some diseases.

     Genetic resistance. Whenever available, the use of resistant
varieties is the best way to prevent disease problems. Response
to disease attack may vary, as indicated by the terms immune,
resistant and tolerant. Disease immunity indicates that a plant
will not get a disease even though the disease is present.
Disease resistance implies that although a plant may occasionally
contact the disease, it is much less likely to get it, and if
attacked, may not be seriously affected. Tolerance to a disease
implies that the plant usually contacts the disease when present
but is able to survive in spite of being infected.
     Resistant varieties are becoming more readily available in
many crops. Look for disease resistance in variety descriptions.
Disease resistance of vegetable varieties is indicated in the
"Vegetable Planting Calendar," Grounds for Gardening Guide 6201.

     Crop rotation. Crop rotation is as old as agriculture
Continued cropping in one area allows for buildup of disease
organisms. Rotating crops each year to help prevent buildup of
organisms in one place can reduce some disease problems. Diseases
such as clubroot and some vascular wilts may persist in the soil
for five or more years without the presence of a susceptible
plant. For these and similar problems, very long rotation times
are necessary.

     Sanitation. Sanitation is important to the control of plant
disease. Destruction of weeds or other plants that may serve as
overwintering host plants, along with elimination of crop plants
that have been diseased, is important. Careful selection of new
plants, seeds or cuttings is important to avoid introduction of
diseases into the garden or landscape.

     Protection. In some cases, careful selection of disease-free
seed and propagating material helps disease control by avoiding
introduction. Certified seed potatoes are a good example of a
case where the use of disease-free seed pieces keeps the soil
clean and protects against inoculating the field with soil
diseases.
     Following are practices that can help control plant
diseases:
     1. Use disease-resistant varieties whenever they are
available, as well as varieties suited to the local growing
conditions.
     2. Select garden locations with good soil drainage, adequate
sunlight, and good soil.
     3. Improve the soil with organic matter and fertilizers to
develop the best soil tilth for growing seeds and plants.
     4. Rotate the garden locations. If the garden space is too
limited for garden rotation, rotate crops within the space
available.
     5. Use disease-free transplants and seeds from reputable
suppliers. Do not plant more than you can take care of properly.
     6. Eliminate weeds around the garden area that may serve to
harbor diseases throughout the year.
     7. Control insect pests that serve as disease carriers.
     8. Pull up and destroy any plants showing diseases, as those
caused by viruses, which can not be controlled. Pull off diseased
leaves as soon as you notice them to help slow the spread of leaf
spots and other fungus diseases.
     9. Spade under or remove and destroy crop residue as soon as
harvest is completed if disease was a problem during the season.
     10. Do not overcrowd plants. Overcrowding prevents good air
movement and exposure to adequate sunlight. High humidity and too
much shade caused by these conditions can increase the
development of some diseases.

Controlling insects
     At one time gardens had few insect problems. The current
movement of people over long distances has helped move pests to
areas where they were once unknown or uncommon. Many more
problems that need control face the modern gardener.
     Many common insect pests can be controlled with modern
chemicals. In avoiding their use, however, you must be willing to
work a little harder and accept some insect damage in your
garden. Following are a few techniques that can help control
insect attack and spread. Some of these are the same as those
used to control disease:
* Since you will not be able to avoid all insect damage, plant
more of a crop for adequate harvest.
* Check crops often and hand pick any insects present before they
become too numerous.
* Encourage natural insect predators when possible.
* Although not common, some plants have insect resistance. Select
them when available.
* Do not plant crops in large blocks. Mixing different types of
plants helps slow the spread of insects that are present.
* The concept of trap crops may also help. These are less
desirable crops planted near the garden. The hope is that insects
will be attracted to and consume these crops more than the
desirable ones.
* Supplement mechanical controls with biological and natural
pesticides. These include dormant oils, lime-sulfur, elemental
sulfur, pyrethrins, rotenone and nicotine. Use these materials
carefully, according to directions of the manufacturer.
* Fertilize, cultivate and water to promote vigorous growth.
Healthy plants seem less attractive to insects, and those that
are attacked are better able to survive and still produce a crop.
* Rotate the crop. Some insects may overwinter in the soil or
other debris. Moving the crop may delay their attack in spring.
* Use transplants when possible. These develop more quickly than
seeds in the garden. The quicker you can grow and harvest the
crop, the less chance of insect pests seriously damaging the
plants.
* Destroy any garden debris or nearby weeds that may serve as
breeding or overwintering places for insects.
* Fall cultivate the garden. This buries deeply or exposes some
insects and insect eggs to birds or to desication during winter
freezing and thawing.
* Keep the garden free of weeds that may harbor pests.

     Biological control of insect pests. The biological control
of insect pests refers to the use of disease organisms,
predacious or parasitic insects, insect-feeding birds, toads, and
other animals.
     When these are used, a certain amount of damage must also be
expected, as these predators are not always present at the time
the insects are numerous, and their increase in numbers usually
follows an increase in the pests. Releasing pests (such as
ladybugs) and predators has been successful in some areas. One of
the most successful biological controls has been the use of a
bacteria, bacillus thuriengensis, for control of cabbage loopers
and cabbage worms in cole crops.
     Remember that when any kind of insect predator is released
in the garden, the pests must already be present to serve for
food. If insects are not present, the predators will move
elsewhere looking for food.

     Soap as an insecticide. Some people suggest that soap is
effective as an insecticide. This recommendation dates back to
the 1700s. Modern soaps vary widely, and their effectiveness as
an insecticide also varies and is sometimes questionable. It
seems that the most effective soap for an insecticide is the old-
fashioned homemade soap prepared from waste lard, tallow, lye and
water. If there is any benefit from these materials, remember
that it comes from some of the more caustic soaps, not
detergents.