Abstract
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This publication covers soil amendments that are not standard agricultural
fertilizers. These include plant and animal by-products, rock powders,
seaweed, innoculants, conditioners and others. Much of the information
is taken from research reports by Iowa State University and the
Rodale Institute Research Center, which cover the material in greater
detail (9, 2, 10).
The reader is referred to these works for additional information.
Another ATTRA publication, Sources
of Organic Fertilizers and Amendments, serves as a companion
piece to this document. It provides sources for the materials discussed
herein.
Table of Contents
Amendments In Proper Context
The sustainability of a farm system is only marginally related
to fertilizer and other inputs. Intrinsic soil factors such as slope,
texture, and local rainfall, along with management-related factors
such as a forage-based rotation, soil organic matter, aggregate
stability, and tillage practices, have a much greater influence
on the sustainability of any given farm than does the type or amount
of soil amendments. Shifting from conventional inputs to alternative
ones does little to increase overall sustainability.
For example, yields of most crops will be reduced in soils with
poor or excessive drainage, and when soil pH is too acidic or alkaline
for the crop's needs. Only if soil moisture, air, and acidity regimes
are generally correct do the major nutrients—nitrogen, phosphate,
and potash—begin to exert significant influence on yields.
In other words, if a soil is excessively acid and poorly drained
it doesn't really matter how much fertilizer (conventional or alternative)
is applied; yields will still be disappointing.
In most cases, alternative products are appropriate and effective
as minor components of a highly developed system of whole-farm management.
They are most effective in fine-tuning a system that already functions
relatively well. This fact is well worth remembering when talking
with vendors at a trade show or planning a product purchase. It
is wise to evaluate their potential usefulness in view of other
use for the same money.
Farmers for whom organic certification is an important element
of marketing should check carefully with their certification program
before buying any product that they do not positively know is approved
on a brand-name basis.
Organic certification programs and their field inspectors have
reported persistent problems with alternative soil amendments other
than the better-known alternative fertilizer materials. Some farmers
have been refused certification because they took the word of a
product promoter and applied an alternative soil amendment without
ensuring that it was approved by the program under which they sought
certification. Some alternative soil amendments either contain ingredients
that disqualify them from use in certified production, or contain
"secret" ingredients that prevent a certification program
from evaluating whether or not that specific brand can be approved.
ATTRA has additional information on organic certification, plus
a list of certifiers, available upon request. ATTRA has some good
introductory material on sustainable soil management; ask for ATTRA
publications Overview
of Cover Crops & Green Manures and Sustainable
Soil Management.
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Plant & Animal By-Products
Assorted by-products of the food and fiber industries are occasionally
used as soil amendments, returning to the land nutrients that might
otherwise be wasted. Many of these products are far too expensive
to justify their use in other than very specialized horticultural
applications.
Plant by-products
Alfalfa meal (or pellets) contains around 3% nitrogen
and is commonly used as an animal feed. It is an excellent fertilizer
material in horticulture, and is said to contain unknown growth
factors which make its mineral content more effective as plant nutrients.
Cottonseed meal is a rich source of nitrogen (7%). Unfortunately,
a substantial percentage of the insecticides used in the U.S. are
applied to cotton, and some of these tend to leave residues in the
seeds. Most organic certification programs restrict or prohibit
the use of cottonseed meal.
Fruit pomaces are what remain after the juice is extracted.
They are heavy, wet products normally available only locally, and
best composted before use.
Leaf compost is increasingly available as more and more
municipalities compost urban and suburban leaves. In principle,
the product is a good one, but it is often contaminated with "impurities"
ranging from transmission fluid to trash bags.
Soybean meal is, like alfalfa, most commonly used as a
protein supplement for animal feeds. With about 7% nitrogen it can
be a useful, but expensive, fertilizer material.
Wood ash contains about 2% phosphate and 6% potash, but
may be contaminated with heavy metals or plastic and typically has
a high salt content. Wood ash is rather alkaline, and excessive
use can be quite damaging to many soils. Some organic programs restrict
its use.
Animal by-products
Blood meal is dried slaughterhouse waste containing about
12% nitrogen. Unless used carefully, it can burn plants with ammonia,
lose much of its nitrogen through volatilization, or encourage fungal
growth. In view of the extremely high cost of blood meal, farmers
should be sure that it really is the best source of nitrogen in
a given situation.
Bone meal is discussed under phosphate sources, in the
section titled "Rock and Mineral Powders."
Feather meal is a common by-product of the poultry slaughter
industry. Although total nitrogen levels are fairly high (7 to 10%),
the nature of feathers is such that they break down and release
their nitrogen much more slowly than many products of similar price.
Fish meal and fish emulsion are, like most animal
by-products, rich in nitrogen. Fish meal contains about
10% nitrogen, along with about 6% phosphate. It is most frequently
used as a feed additive, but can be used as a fertilizer. The fertilizer
analysis of fish emulsion varies with preparation method.
Whole fish and fish parts must be digested to form a slurry, a process
accomplished with the aid of either phosphoric acid or special enzymes.
Acid-digested fish emulsion usually has an analysis around 4-4-1,
while enzyme-digested fish emulsion is usually measured as 4-1-1.
Fish emulsion may be fortified with chemical fertilizer, so organic
farmers should be suspicious of any product with a nitrogen content
in excess of 5%.
Leather meal is ground tannery waste with 10% nitrogen.
Unfortunately, most leather meal also contains about 3% added chromium
(a toxic heavy metal), and is thus prohibited in organic agriculture.
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Manure- and Compost-Based Products
One of the most common types of prepackaged alternative soil amendments
is the manure- or compost-based blended fertilizer. Several of these
products have national distribution, and many more enjoy a loyal
regional following. Such products are typically analyzed at 2 to
5% for each nutrient. Dried compost is used as a bulking agent,
source of nutrients, and organic matter. It is blended with several
of the materials discussed in this publication, including rock minerals
and plant and animal by-products. Nearly all products of this class
sell for prices about three times greater than their conventional
fertilizer value, but may be quite effective in farm situations.
However, farmers with access to other sources of manure or compost
can realize substantial savings by relying on local manure resources.
Some manure-based, blended fertilizers contain ingredients prohibited
by one or more organic certification programs and may not be used
in certified production; others may be disqualified because the
manufacturer refuses to reveal the "secret" ingredients.
Composted sewage sludge is marketed as a fertilizer and soil amendment.
This compost provides organic matter and a number of nutrients,
and as marketed, is solid with little odor. The greatest potential
problems with using composted sludge are heavy metals from industrial
waste, along with assorted chemical contaminants (from household
cleaners, latex paint, and other things people flush down their
drains). Pathogens are controlled fairly easily through proper composting,
which raises the temperature of the composting material sufficiently
to kill many microorganisms. The U.S. Environmental Protection Agency
has established strict guidelines for pathogen control, which most
sewage composting facilities follow.
Heavy metal contamination is a significant risk wherever industrial
facilities contribute to sewage. Contamination by heavy metals and
many other chemicals is limited as much as possible with current
technology, but composted sludge often contains levels that make
it unsuitable for use on food crops. Before using any composted
sludge or other treated municipal waste product in crop production,
the grower must know the chemical composition of the product and
whether it is safe to apply to food crops. Have the sludge tested.
It is important to note that at least 38 states regulate the production
of sewage compost. Its use is prohibited in all certified organic
production.
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Rock And Mineral Powders
Phosphate sources
There are a number of alternative phosphate sources on the market,
but it can be difficult for growers to determine which is the most
appropriate for their operation. Much of the difficulty stems from
confusion about the difference between "total" and "available"
phosphate. Chemical phosphate fertilizer is sold on the basis of
available phosphate expressed as P2O5. In fact, "available
phosphate" is the only allowable claim for fertilizer value.
Available phosphate designations are determined by measuring the
amount of phosphate that dissolves in a weak citric acid solution
believed to imitate conditions near plant roots. This test provides
a standard means of comparing different phosphate sources. Unconventional
phosphates, because of their slow release, are often promoted on
the basis of total phosphate content. Neither available nor total
phosphate analyses give a particularly accurate picture of how different
phosphate materials will perform in natural systems, hence the importance
of developing good powers of observation through on-farm experimentation.
A general understanding of the principal phosphate products, however,
will give some indication of how they are likely to act in different
circumstances. Of particular importance is soil pH; phosphates will
be released more quickly in moderately acid soils than in neutral
or alkaline soils.
Colloidal phosphate consists of clay particles surrounded
by natural phosphate. Total phosphate is around 20% and "available"
phosphate about 2-3%. An efficient use of colloidal phosphate is
to add it directly to livestock manure in the barn or lot, where
the manure acids dissolve much of the total phosphate and the phosphate
stabilizes the nitrogen in the manure. Many of the same advantages
can be had by adding 20-50 pounds of colloidal phosphate to one
ton (two cubic yards) of manure when composting. The ATTRA publication
Farm-scale Composting
Resource List
directs the reader to many useful resources on composting. When
direct land application of rock phosphate is the only possibility,
spreading rates between 500 and 2,000 pounds per acre are appropriate,
depending on phosphorus status, soil acidity, and finances.
Rock phosphates are usually derived from ancient marine
deposits. They have a different composition than collodial phosphate,
generally making them less available. Total phosphate is around
30% and available phosphate 1-2%. They are best used in the same
manner as colloidal phosphate, and it is worth paying for several
tests to determine how effectively this phosphate moves into manure
and soil. It may or may not be a better buy than colloidal, depending
greatly on conditions and circumstances.
Hard-rock phosphates are usually derived from igneous
volcanic deposits and consist almost totally of the mineral apatite.
Although apatite contains about 40% total phosphate, because of
the mineral's composition, this phosphate is largely unavailable.
In most circumstances it is not a good buy, but in some situations
is the ideal product; again, trial and observation are the keys
to a wise purchase.
Bone meal is so well known, especially in horticulture,
that it can hardly be considered an alternative product. Typically
it contains about 27% total phosphate, and nearly all of that is
available. There is a great deal of confusion about the phosphate
content of bone meal because much of it is sold as a feed additive.
In the feed industry, phosphorus is expressed on the label as elemental
phosphorus, while in the fertilizer industry it is expressed as
phosphate. Phosphate gives a much bigger number (2.3 times as big)
for the same actual phosphorus content. Twelve percent phosphorus
is the same as 27% phosphate, and bone meal is sold under either
of those (or similar) numbers; it's the same good, but expensive,
product in either case.
A by-product of the smelting industry, basic slag may,
if finely ground, be a source of phosphorus and minor elements.
Use of basic slag in organic production is restricted.
Potassium from rock and mineral powders
Alternative potash (potassium) sources are similar to alternative
phosphates in that there are a variety of sources, with differing
availability and fertility value. As with phosphate, there is a
difference between available potash and total potash; similarly,
there is a difference between pure potassium and potash, with the
potash number being 1.2 times higher than potassium for the same
amount of nutrient.
Two sources of potash, potassium sulfate and potassium
magnesium sulfate (langbeinite), are commonly enough used in
conventional agriculture that they can hardly be considered alternative,
save for the fact that both are regularly used in certified organic
agriculture. There are two forms of potassium sulfate on the market.
One is derived by reacting sulfuric acid with potassium chloride.
It is a good fertilizer, but not acceptable in certified organic
production. Natural potassium sulfate, from Great Salt Lake, is
extracted by a differential evaporation process lasting three years.
It can be used in organic farming. Langbeinite goes from mine to
field with minimal processing. Sulpomag® and K-Mag® are
two brand names for langbeinite.
The salt content and solubility of potassium-bearing sulfates dictate
well-considered use, but their high potash content (22% for langbeinite
and 50% for potassium sulfate) does allow for good plant response
from relatively modest application rates. Although soluble salts,
these products are considerably less salty and less soluble than
either kainite (a mixture of potassium sulfates and common salt)
or muriate of potash, the most common conventional potassium fertilizer.
Granite dust is often sold as a "slowly available"
potash source for organic production. Total potash contents in granite
dust typically vary from 1 to 5%, depending on overall mineral composition
of the rock, but granite is mostly feldspar, a mineral with low
solubility. Therefore, little potash fertility is derived from this
material.
Another source of slowly available potash, popular in alternative
agriculture, is the clay-type mineral, glauconite, commonly sold
as greensand. Total potash content of greensand is around
7%, all of which is deeply locked into the mineral and only slowly
available. Greensand is also said to have desirable effects on soil
structure. Its high price, however, limits its use solely to high-value
horticultural applications.
Feldspar is one of the major potassium-bearing minerals
of granite. Feldspar powder is fairly easily obtained through the
ceramics trade. Unfortunately, most feldspar potash is as tightly
bound within its mineral structure as is the potash in greensand.
Unless particular circumstances provide a clear indication that
feldspar is the most appropriate source of potash, it is proabably
not cost-effective.
Certain micas, particularly biotite (black mica), contain
several percent total potash, which, because of mica's physical
structure (quite different than feldspar or glauconite), is relatively
available in microbially active environments. If pure biotite can
be obtained at a reasonable price, it may be cost-effective and
useful.
A by-product of the cement industry, kiln dust can be
an affordable limestone substitute and potash (about 6% soluble)
source in areas where it is available. Some cement kilns are fired
using assorted industrial wastes, sometimes including hazardous
wastes. Dust from these kilns may itself be a hazardous product,
and in several states is legally treated as such. Sources should
be verified carefully, and state regulations checked. To date, the
product is sold only in bulk. It is generally prohibited in certified
organic production.
Secondary and minor nutrients from rock powders
A number of other rock dusts and powders are occasionally available
in various parts of the country; sometimes the results from local
trials are reported in national or international publications, but
it is important to remember that what applies in one region may
not be pertinent in another. Additionally, when dealing with natural
materials like rock, there is very little product consistency from
one batch to another; results from one trial may not be transferable
to other situations.
Basalt dust, if available at a reasonable cost, can provide
a wide range of trace minerals to agricultural systems over a period
of several years; as with most rock powders, transportation costs
are a major factor in determining cost-effectiveness. Most of the
rich volcanic soils of
the world are derived from basalt, which gives some indication of
basalt's agronomic value, and even when too expensive for land application,
basalt dust can benefit farm systems when mixed with manure in the
composting process.
Any rock, of course, can be ground into powder, if the price is
right. Various people have proposed additions to the soil of assorted
rock dusts, or even powdered gravel. One rationale for this is the
paramagnetic property that some rock minerals add to the soil—a
factor believed to be associated with high fertility. ATTRA has
additional information on paramagnetism in soils for those interested.
Zeolites
Zeolites are mined alumino-silicate materials, containing only
insignificant levels of plant nutrients. Their use in crop production
stems primarily from high nutrient-exchange capacities, which allow
them to absorb and release plant nutrients and moisture without
any change in the nature of the zeolite. This action results from
the mineral's porous-but-stable chemical structure.
Zeolites enhance the performance of fertilizers by making them
resistant to leaching, immobilization, and gaseous losses. They
are of particular use in reducing leaching in sandy soils. In one
study, 4 to 8 tons of zeolite per acre was applied (1).
Yield increases were reported for wheat (14%), eggplant (19-55%),
carrots (63%), and apples (13-38%). Zeolites are widely used in
eastern European and Japanese agriculture, but their use in the
U.S. at this time is very limited.
Humates
Humates are commercial products usually prepared from leonardite,
an oxidized form of lignite coal and clay. Leonardite may contain
up to 60% humic and fulvic acids, which mimic the "active"
part of soil humus. Soil scientists use very broad definitions to
describe soil organic matter components; "fulvic acids"
and "humic acids" are terms lumping complex families of
organic compounds together on the basis of how they can be most
easily extracted from soil. For the most part, however, the organic
acids extracted from leonardite bear little resemblance to the humic
or fulvic acids in soils. Although extremely useful and cost-efficient
in certain situations—as nutrient substrates in soilless greenhouse
production for example—humates and similar products are less
clearly helpful in many field situations.
The sheer volume of organic matter in even moderately rich soils
suggests that agronomically affordable applications of humates may
not produce significant improvements. The top six inches of soil
weigh approximately 1,000 tons per acre; each percent of organic
matter, therefore, weighs ten tons. Even assuming that the organic
matter in humate products actually is similar to that in soil, it
requires two tons of humates per acre to increase soil organic matter
by 0.1%.
Research by the Rodale Institute determined that:
commercial humates...are not products that can
substitute for adequate mineral nutrients.... Humates do contain
high percentages of humic acids and organic matter, but at their
recommended, or economically feasible rates it is likely they
may not significantly increase soil organic matter. Likewise,
the humic acids in commercial humates may have the ability to...provide
growth-stimulating effects, but in the soil they comprise only
a minute fraction of the total soil humic acid content (2).
Additionally, the results indicated that humates containing unrefined
leonardite can immobilize soil phosphorus under some conditions,
creating a negative effect on plant performance.
The Rodale report also concluded that:
[while] humate products are based on sound principles
and the potential for their beneficial action does exist...the
economics and time involved to increase organic matter through
commercial products, rather than through more traditional organic-matter-building
programs, should be seriously considered (2).
Despite such determinations, many farmers report significant benefits
from the use of humates and related products. Where humates have
shown the most promise is as natural soil amendments in areas with
alkaline, low-organic-matter soils. Such soils are common across
a wide range of agricultural production zones in the southern and
western U.S. Leonardite and similar products are generally consistent
with organic production practices, given that they are natural products
with proven benefit in certain situations. Some extracts, however,
are not acceptable in certified organic production, depending on
the extraction process used.
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Seaweed Products
Most seaweed fertilizers come from kelp that has been harvested,
dried, and ground. Kelp meal is suitable for application directly
to the soil, or for addition to the compost pile. It flows easily
and is readily applied with most dry fertilizer applicators. It
is easily mixed with other dry fertilizers and amendments.
Soil application rates for kelp meal commonly range from 150 to
250 lbs/acre for pastures, forages and small grains. Two hundred
to 400 lbs/acre are advised for corn, horticultural crops, and gardens.
Since it is expensive, kelp meal is most commonly used only on high-value
crops.
Dried raw seaweed tends to contain about 1% nitrogen, a trace of
phosphorus, and 2% potash, along with magnesium, sulfur, and numerous
trace elements. Raw seaweeds are prepared by various methods and
sold under a number of brand names.
More often, compounds from kelp and other seaweeds are extracted
by various methods in order to concentrate both micronutrients and
naturally occurring plant hormones into a soluble, easily transported
form. Such kelp extracts are sometimes applied as a foliar
spray by farmers seeking a natural source of micronutrients. For
the most part, none of the micronutrient levels in kelp extracts
is high enough to correct a deficiency, but as a "tonic"
providing a broad array of micronutrients and other trace elements,
seaweed extracts have won a measure of acceptance among organic
farmers. Note that while most kelp products are allowed in certified
production, a few have been supplemented with commercial forms of
potash and other nutrients and are prohibited.
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Microbial Inoculants
Inoculants, which are dry or liquid preparations of one or more
species of microorganism, fall into three broad groups: 1) those
that inoculate individual plants with symbiotic organisms (chiefly
Rhizobia spp.), 2) those that inoculate the soil with desirable
organisms, and 3) those that are used as "cover crops"
(algae).
Rhizobia
The most clearly beneficial microbial preparations for agricultural
use are the different strains of Rhizobia used to inoculate
legumes. Specific strains of these bacteria live in a mutually beneficial
(symbiotic) relationship with specific species of legumes. The bacteria
penetrate the plant roots, causing the formation of root nodules
containing both plant tissue and bacteria. In very simple terms,
the plant supplies the physical environment and certain nutrients
to the bacteria; the bacteria "fix" nitrogen from the
air into compounds that then become available to the plant. Typical
nitrogen fixation rates vary from 50 lbs/acre to over 300 lbs/acre,
depending on climate, species, and soil conditions. On most farms
these rates make it possible to harvest good crops without purchasing
additional nitrogen.
Mycorrhizae
The mycorrhizae (my-cor-ry-'zee) group of fungi live either on
or in plant roots and act to extend the reach of root hairs into
the soil. Mycorrhizae increase the plant's uptake of water and nutrients,
especially in less fertile soils. The superfine, root-like structures
of these fungi are more extensive and more effective than plant
root hairs at absorbing phosphorus, and other nutrients as well.
Phosphorus moves slowly in soils but the fungi can absorb it much
faster than the plant alone can. This enhanced root feeding makes
it possible to reduce fertilizer rates for plants having a healthy
colony of mychorrhizae. Some plants including citrus, grapes, avocados,
and bananas, are dependent on mycorrhiza fungi. Others that benefit
from having them are artichokes, melons, tomatoes, peppers, and
squash.
Roots colonized by mycorrhizae are less likely to be penetrated
by root-feeding nematodes since the pest cannot pierce the thick
fungal network.
Mycorrhizae also produce hormones and antibiotics, which enhance
root growth and provide disease suppression. The fungi benefit from
plant association by taking nutrients and carbohydrates from the
plant roots they live in.
In soils where mychorrhizae have been killed off, an inoculation
may be beneficial. In healthy soils where they already exist there
will be little or no benefit to adding more. There are dozens of
mychorrizae species in nature. Additionally, the species found on
plant roots may change as the plant matures. If those that are available
are of the correct species, and are handled properly at all stages,
they offer interesting potential benefits to farmers in well-managed
systems. Generally it is preferred to inoculate with several species
rather than a single one. For information on rhizobial and mycorrhizal
inoculation for disease suppression, request the ATTRA publication
Sustainable Management
of Soil-borne Plant Diseases.
Free-living soil organisms
A great many of the products in this category are designed to be
sprayed on the soil surface or on crop residues in order to inoculate
the topsoil with desirable microorganisms. Manufacturers of these
products make numerous and varying claims about their beneficial
effects, which fall into three broad categories:
- The microbes will fix enough nitrogen from the air to allow
the farmer to eliminate much or all fertilizer.
- The product improves soil organic matter and "releases"
soil nutrients to the crop.
- The product produces better yields, especially during times
of drought.
Many microbial products do indeed contain free-living (as opposed
to symbiotic) microbes that are known to fix nitrogen in certain
circumstances. Those species, however, work best in wet, oxygen-poor
conditions that most farmers and their crops would prefer to avoid.
Rice paddies are a notable exception. In the vast majority of cropping
situations other than rice production, the amount of nitrogen fixed
by such free-living microbes is not generally considered economically
significant (3). In other words, the value of
any fixed nitrogen may be less than the cost of the product. Far
greater nitrogen fixation, for example, can be obtained via symbiotic
Rhizobia on a legume sod or cover crop, for much lower
cost.
Soil microbes, like all living things, will thrive only in the
presence of their preferred environmental conditions-moisture, oxygen,
temperature, pH, food, and shelter. When conditions are not within
favorable ranges, the microbes cease reproduction or die. Natural
microbial populations will be abundant if soil conditions are right.
Adding a microbial amendment in such circumstances may not be cost-efficient,
because the naturally occurring individuals will typically outnumber
the same species supplied in a product by 10,000 to 1, or more (4).
If soil conditions are not right, inoculant organisms will reproduce
just as slowly as their naturally occurring colleagues, which is
to say, not at all. The consensus among agronomists appears to be
that these products perform best when the soil is at or near optimum
conditions to begin with.
Algal mats
Another group of inoculants, sold as "cover crops," are
commercial preparations of soil-inhabiting algae advertised as providing
many benefits, including reduced soil crusting, improved soil structure,
increased soil organic matter, improved drainage, and better moisture
retention. A solution of the algae mixed with water is sprayed on
the soil surface. In theory it then establishes itself to form a
continuous mat over the soil surface. If natural algae populations
have not been observed to populate a particular soil already, management
practices will have to be adjusted to get successful growth of an
algal cover crop.
Algae are susceptible to the vast majority of herbicides in use
today and would therefore be essentially incompatible in a conventional
row crop system. Mat establishment could only occur in the absence
of soil disturbance. Therefore, application would need to be made
only after a final cultivation. Lastly, a continuously moist surface
is necessary. On most soils this would require irrigation.
Where weed management is a concern, a traditional cover crop will
be more effective than algae. The algal mat is very thin and will
not suppress weeds adequately. The constant surface moisture required
by the algae tends to encourage weed seeds to sprout. It can also
encourage disease problems in the crop.
Enzyme-Based Amendments
Enzymes are involved in a number of soil reactions, particularly
as catalysts in the microbial breakdown of organic matter, but very
little research has been done on the effects of adding enzyme products
to the soil. Nevertheless, commercial enzyme treatments for soils
are often advertised as having a large number of beneficial effects,
including improved soil structure, nutrient "activation,"
greater nutrient availability, "detoxification" of the
soil, better drainage, better water retention, and greater microbial
activity.
In nature, the microorganisms that process soil organic matter
produce the enzymes they need to do the job. Those enzymes, being
proteins, are themselves broken down by microbial action (5).
Enzymes added to the soil would probably suffer a similar fate in
short order.
As with free-living soil organism products, the circumstances where
enzyme products are likely to perform the best are in soils, that
are already well-balanced and in good condition.
Vitamin products are also sold as soil treatments on occasion,
but more often as sprays for the plants themselves. Plants might
absorb some of the vitamin through leaves or roots, but much of
the applied vitamin is broken down into simple components before
being absorbed by the plant (6, 7).
Generally, plants in favorable environments synthesize all the vitamins
they need from the resources at hand. The most likely benefit of
applying a vitamin product would be as a "quick fix" measure
for plants grown under poor conditions, provided it is possible
to determine just which vitamins happen to be deficient.
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Soil Conditioners
Wetting agents and surfactants break the natural surface tension
of water, overcoming its tendency to form droplets, and allowing
it to penetrate a variety of materials. Common clothes-washing solutions,
shampoos, and detergents rely on wetting agents or surfactants to
function effectively. Similar compounds are also sold as soil conditioners
and are heavily promoted as improving water penetration, drainage,
and soil structure. They are also advertised as aids in controlling
erosion and reducing compaction or hardpans as a result of increased
water penetration of the soil.
In general, wetting agents are effective where a soil's water-repellency
is caused by turf or grassland cover, by ash from the burning of
organic matter, or by single-grain soil structure (soil particles
all of one size and not aggregated, as occurs in some sands). Conditions
in which wetting agents have little or no effect include poor drainage
due to hardpans, compaction from tillage or traffic, and "tight"
or fine-textured soils that have very small pores (such as some
clays). In other words, wetting agents are likely to have some effect
where water infiltrates a soil slowly because the soil surface repels
water, but not where water penetrates slowly because there are no
large pore spaces (8). Most soils with good
structure have good infiltration rates. Soil structure can be maintained
and improved by a good rotation, regular additions of organic matter,
and normal conservation practices. Beneficial effects should not
be expected on soils that are already wetable.
Commercial wetting agents can be quite expensive, especially when
used to treat large areas, and any results may not justify the cost
of the product. Some farmers attempt to economize by applying something
like dishwashing soap or shampoo instead of commercial wetting agents,
but caution is advised since other ingredients in household products
may be detrimental to plant growth or may cause a breakdown of soil
structure. Note, too, that many wetting agents are not acceptable
in certified organic production.
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Evaluate Products Carefully
Some non-traditional soil treatments are based on sound biological
or scientific principles. Unfortunately, a number of studies cited
in the Compendium (9, 10)
and in the Rodale report Novel Soil Amendments (2)
show that using many of the non-traditional products mentioned here
results in negative net income for the
farmer. The supposed beneficial effects of the products tested in
these studies do not increase yields sufficiently to offset the
cost of applying the product. In many studies, the product tested
had no measurable effect on either the crop or the soil.
Advertisements for these products often cite studies which the
sellers claim prove the effectiveness of their products. Those results,
however, are usually taken out of context, obscuring the fact that
the claimed yield increase is due not to the tested product, but
to normal random fluctuations in yield caused by environmental conditions
within the study. In other words, the product doesn't really do
what the vendors claim it does. Though governments do require companies
to guarantee analyses and to back up sales claims for conventional
fertilizers, alternative products are, for the most part, unregulated
and uncontrolled.
At the same time, prejudice against alternative products and practices
has often resulted in testing that has been less than honest, and
some off-the-cuff rejections by researchers and Extension. As a
result, farmers benefit the most by evaluations done within the
context of their own farm operations. On-farm research trials take
some effort but are not difficult to perform. Contact ATTRA for
a copy of the Sustainable Agriculture Network's publication entitled
How to Conduct
Research on Your Farm or Ranch.
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References
- Mumptom, Fredrick A. 1985. Using
zeolites in agriculture. p. 125-158 In: Innovative Biological
Technologies for Lesser Developed Countries. Congress of the United
States, Office of Technology Assessment. Washington D.C. 246 p.
- McAllister, J. 1987. A Practical
Guide to Novel Soil Amendments. Rodale Press, Emmaus, Pennsylvania.
124 p.
- Huang, P. M. and Schnitzer, M.,
ed. 1986. Interactions of Soil Minerals with Natural Organics
and Microbes, Special Publication. 17. Soil Science Society of
America, Madison, Wisconsin. 606 p.
- David Patriquin
Department of Biology
Dalhousie University
Halifax Nova Scotia
- Stevenson, F. J., ed. 1982. Nitrogen
in Agricultural Soils. American Society of Agronomy. Madison,
Wisconsin. 940 p.
- Vitosh, M. L. 1984. Biological
Inoculants and Activators: Their Value to Agriculture. North Central
Regional Extension Publication. 168. 4 p.
- Allison, F.E. 1973. Soil Organic
Matter and its Role in Crop Production. Elsevier Scientific Publishing
Co., New York, 639 p.
- Sunderman, H. D. 1983. Soil Wetting
Agents: Their Use in Crop Production. North Central Regional Extension
Publication 190, 4 p.
- NRC-103 Committee. 1986. Compendium
of Research Reports on Use of Non-Traditional Materials for Crop
Production, Cooperative Extension Service, Iowa State University,
Ames. Varied pagination.
- Ibid. Supplement 1
Alternative Soil Amendments
By Preston Sullivan
NCAT Agriculture Specialist
Cole Loeffler, HTML Production
IP 054
Slot 132
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