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BENEFICIAL AND EFFECTIVE MICROORGANISMS FOR A SUSTAINABLE AGRICULTURE AND ENVIRONMENT

 

 

Dr. Teruo Higa

 

Professor of Horticulture

University of the Ryukyus

Okinawa, Japan

 

and

Dr. James F. Parr

Soil Microbiologist

Agricultural Research Service

US. Department of Agriculture

Beltsville, Maryland, USA

International Nature Farming Research Center

Atami, Japan

1994

 

TABLE OF CONTENTS

 

*

1. THE CONCEPT OF EFFECTIVE MICROORGANISMS:

THEIR ROLE AND APPLICATION *

2. UTILIZATION OF BENEFICIAL MICROORGANISMS IN

AGRICULTURE *

2.1 What Constitutes an Ideal Agricultural System. *

2.2 Efficient Utilization and Recycling of Energy *

2.3 Preservation of Natural Resources and the Environment. *

2.4 Beneficial and Effective Microorganisms for a Sustainable

Agriculture *

2.4.1 Optimum Yields of High Quality Crops *

3. CONTROLLING THE SOIL MICROFLORA:

PRINCIPLES AND STRATEGIES *

3.1 Principles of Natural Ecosystems and the Application of

Beneficial and Effective Microorganisms *

3.2 Controlling the Soil Micro flora for Optimum Crop Production

and Protection *

3.3 Application of Beneficial and Effective Microorganisms: A New

Dimension *

3.4 Application of Beneficial and Effective Microorganisms:

Fundamental Considerations *

4. CLASSIFICATION OF SOILS BASED ON THEIR

MICROBIOLOGICAL PROPERTIES *

4.1 Functions of Microorganisms: Putrefaction, Fermentation, and

Synthesis *

4.2 Relationships Between Putrefaction, Fermentation, and

Synthesis *

4.3 Classification of Soils Based on the Functions of

Microorganisms *

4.3.1 Disease-Inducing Soils *

4.3.2 Disease-Suppressive Soils *

4.3.3 Zymogenic Soils *

4.3.4 Synthetic Soils *

SUMMARY AND CONCLUSIONS *

REFERENCES *

 

 

In 1989, the National Research Council of the National Academy of Sciences

issued a highly significant report on "Alternative Agriculture" which was

defined as a system of food and fiber production that applies management

skills and information to reduce costs, improve efficiency, and maintain

production levels through such practices as crop rotations, proper integration

of crops and livestock, nitrogen fixing legumes, integrated pest management,

conservation tillage, and recycling of on-farm wastes as soil conditioner: and

biofertilizers. The report encouraged the collective adoption of these practices

by U.S. farmers as the best alternative to the continued and intensive use of

chemical fertilizers and pesticides which have often impaired the quality of our

soil, water, and food.

Again, in 1993 the National Academy of Sciences left no doubt as to these

earlier concerns when the National Research Council released a report on

"Pesticides in the Diets of Infants and Children" which concluded that people

in this age group could be at considerable health risk from consumption of

foods containing pesticide residues.

Both of these reports have raised considerable speculation about the future of

our chemical-based agricultural production system. A growing consensus of

consumers, environmentalists, legislators, and many farmers is that our

current farming practices will have to change considerably to achieve a

significant reduction in pesticide usage in U.S. agriculture. The ultimate goal

of sustainable agriculture according to the National Research Council, and

other sources as well, is to develop farming systems that are productive,

profitable, energy conserving, environmentally sound, conserving of natural

resources, and that ensure food safety and quality. Consequently, the leading

question that U.S. farmers are asking is, "How can I make these changes,

reduce my chemical inputs, and achieve an acceptable level of economic and

environmental sustainability?"

A successful transition from chemical-based farming systems to a more

sustainable agriculture will depend largely on what farmers do to improve and

maintain the quality of their agricultural soils. Indeed, soil quality is the "key" to

a sustainable agriculture. Not surprisingly, the alternative agricultural practices

advocated by the National Research Council are mainly those that can

improve and maintain soil quality. Experience has shown that the transition

from conventional agriculture to nature farming or organic farming can involve

certain risks, such as initially lower yields and increased pest problems. Once

through the transition period, which might take several years, most farmers?

find their new farming systems to be stable, productive, manageable and

profitable without pesticides.

Dr. Teruo Higa, Professor of Horticulture, University of the Ryukyus, Okinawa,

Japan has conducted pioneering work in advancing the concept of "Effective

Microorganisms" (EM). He has developed microbial inoculants that have been

shown to improve soil quality, crop growth and yield and have gained attention

worldwide. As farmer: seek to change from chemical-based, conventional

farming systems to more sustainable kinds of agriculture they will need to

utilize the most effective means available if they are to be successful.

Certainly, this includes the aforementioned alternative agricultural practices

recommended by the National Research Council. We view EM technology as

a potentially valuable tool that can help farmer: develop farming systems that

are economically, environmentally, and socially sustainable.

 

 

Dr. James F. Parr

Agricultural Research Service

U.S. Department of Agriculture

Beltsville, Maryland, USA

 

 

INTRODUCTION

 

 

The uniqueness of microorganisms and their often unpredictable nature and

biosynthetic capabilities, given a specific set of environmental and cultural

conditions, has made them likely candidates for solving particularly difficult

problems in the life sciences and other fields as well. The various ways in

which microorganisms have been used over the past 50 years to advance

medical technology, human and animal health, food processing, food safety

and quality, genetic engineering, environmental protection, agricultural

biotechnology, and more effective treatment of agricultural and municipal

wastes provide a most impressive record of achievement. Many of these

technological advances would not have been possible using straightforward

chemical and physical engineering methods, or if they were, they would not

have been practically or economically feasible.

Nevertheless, while microbial technologies have been applied to various

agricultural and environmental problems with considerable success in recent

years, they have not been widely accepted by the scientific community

because it is often difficult to consistently reproduce their beneficial effects.

Microorganisms are effective only when they are presented with suitable and

optimum conditions for metabolizing their substrates Including available water,

oxygen (depending on whether the microorganisms are obligate aerobes or

facultative anaerobes), pH and temperature of their environment. Meanwhile,

the various types of microbial cultures and inoculants available in the market

today have rapidly increased because of these new technologies. Significant

achievements are being made in systems where technical guidance is

coordinated with the marketing of microbial products. Since microorganisms

are useful in eliminating problems associated with the use of chemical

fertilizers and pesticides, they are now widely applied in nature farming and

organic agriculture (Higa, 1991; Parr et al 1994).

Environmental pollution, caused by excessive soil erosion and the associated

transport of sediment, chemical fertilizers and pesticides to surface and

groundwater, and improper treatment of human and animal wastes has

caused serious environmental and social problems throughout the world.

Often engineers have attempted to solve these problems using established

chemical and physical methods. However, they have usually found that such

problems cannot be solved without using microbial methods and technologies

in coordination with agricultural production (Reganold et al., 1990; Parr and

Hornick, l992a).

For many years, soil microbiologists and microbial ecologists have tended to

differentiate soil microorganisms as beneficial or harmful according to their

functions and how they affect soil quality, plant growth and yield, and plant

health. As shown in Table 1, beneficial microorganisms are those that can fix

atmospheric nitrogen, decompose organic wastes and residues, detoxify

pesticides, suppress plant diseases and soil-borne pathogens, enhance

nutrient cycling, and produce bioactive compounds such as vitamins,

hormones and enzymes that stimulate plant growth. Harmful microorganisms

are those that can induce plant diseases, stimulate soil-borne pathogens,

immobilize nutrients, and produce toxic and putrescent substances that

adversely affect plant growth and health.

A more specific classification of beneficial microorganisms has been

suggested by Higa (1991; 1994; 1995) which he refer to as "Effective

Microorganisms" or EM. This report presents some new perspectives on the

role and application of beneficial microorganism, including EM, as microbial

inoculants for shifting the soil microbiological equilibrium in ways that can

improve soil quality, enhance crop production and protection, conserve natural

resources, and ultimately create a more sustainable agriculture and

environment The report also discusses strategies on how beneficial

microorganisms, including EM. can be more effective after inoculation into

soils.

 

 

THE CONCEPT OF EFTECTIVE MICROORGANISMS:

THEIR ROLE AND APPLICATION

 

 

The concept of effective microorganisms (EM) was developed by Professor

Teruo Higa, University of the Ryukyus, Okinawa, Japan (Higa, 1991; Higa and

Wididana, 1991a). EM consists of mixed cultures of beneficial a naturally occurring

microorganisms that can be applied as inoculants to increase the

microbial diversity of soils and plant. Research has shown that the inoculation

of EM cultures to the soil/plant ecosystem can improve soil quality, soil health,

and the growth, yield, and quality of crops. EM contains selected species of

microorganisms including predominant populations of lactic acid bacteria and

yeasts and smaller numbers of photosynthetic bacteria, actinomycetes and

other types of organisms. All of these are mutually compatible with one

another and can coexist in liquid culture.

EM is not a substitute for other management practices. It is, however, an

added dimension for optimizing our best soil and crop management practices

such as crop rotations, use of organic amendments, conservation tillage, crop

residue recycling, and bio control of pests. If used properly, EM can

significantly enhance the beneficial effects of these practices (Higa and

Wididana, 1991b).

Throughout the discussion which follows, we will use the term "beneficial

microorganisms" In a general way to designate a large group of often

unknown or ill-defined microorganisms that interact favorably in soils and with

plants to render beneficial effects which are sometimes difficult to predict. We

use the term "effective microorganisms" or EM to denote specific mixed

cultures of known, beneficial microorganisms that are being used effectively

as microbial inoculants.

 

 

UTILIZATION OF BENEFICIAL MICROORGANISMS IN AGRICULTURE

 

What Constitutes an Ideal Agricultural System?

 

 

Conceptual design is important in developing new technologies for utilizing

beneficial and effective microorganisms for a more sustainable agriculture and

environment. The basis of a conceptual design is imply to first conceive an

ideal or model and then to devise a strategy and method for achieving the

reality. However it is necessary to carefully coordinate the materials, the

environment, and the technologies constituting the method. Moreover one

should adopt a philosophical attitude in applying microbial technologies to

agricultural production and conservation systems.

There are many opinions on what an ideal agricultural system is. Many would

agree that such an idealized system should produce food on a long-term

sustainable basis. Many would also insist that it should maintain and improve

human health, be economically and spiritually beneficial to both producers

and consumers, actively preserve and protect the environment, are self-contained

and regenerative, and produce enough food for an increasing world

population (Higa, 1991).

 

 

Efficient Utilization and Recycling of Energy

 

 

Agricultural production begins with the process of photosynthesis by green

plants which requires solar energy, water, and carbon dioxide. It occurs

through the plants ability to utilize solar energy in "fixing" atmospheric carbon

into carbohydrates. The energy obtained is used for further biosynthesis in the

plant, including essential amino acids and proteins. The materials used for

agricultural production is abundantly available with little initial cost. However,

when it is observed as an economic activity, the fixation of carbon by

photosynthesis has an extremely low efficiency mainly because of the low

utilization rate of solar energy by green plants. Therefore, an integrated

approach is needed to increase the level of solar energy utilization by plants

so that greater amounts of atmospheric carbon can be converted into useful

substrates (Higa and Wididana, 1991a).

Although the potential utilization rate of solar energy by plants has been

estimated theoretically at between 10 and 20%, the actual utilization rate is

less than 1%. Even the utilization rate of C4 plants, such as sugar cane

whose photosynthetic efficiency is very high, barely exceeds 6 or 7% during

the maximum growth period. The utilization rate is normally less than 3% even

for optimum crop yields.

Past studies have shown that photosynthetic efficiency of the chloroplasts of

host crop plants cannot be increased much further; this means that their

biomass production has reached a maximum level. Therefore, the best

opportunity for increasing biomass production is to somehow utilize the visible

light, which chloroplasts cannot presently use, and the infrared radiation;

together, these comprise about 80% of the total solar energy. Also, we must

explore ways of recycling organic energy contained in plant and animal

residues through direct utilization of organic molecules by plants (Higa and

Wididana, 1991a).

Thus, it is difficult to exceed the existing limits of crop production unless the

efficiency of utilizing solar energy is increased, and the energy contained in

existing organic molecules (amino acids, peptides and carbohydrates) is

utilized either directly or indirectly by the plant. This approach could help to

solve the problems of environmental pollution and degradation caused by the

misuse and excessive application of chemical fertilizers and pesticides to

soils. Therefore, new technologies that can enhance the economic-viability of

farming systems with little or no use of chemical fertilizers and pesticides are

urgently needed and should be a high priority of agricultural research both

now and in the immediate future (National Academy of Sciences, 1989; 1993).

 

 

Preservation of Natural Resources and the Environment

 

 

 

The excessive erosion of topsoil from farmland caused by intensive tillage and

row-crop production has caused extensive soil degradation and also

contributed to the pollution of both surface and groundwater. Organic wastes

from animal production, agricultural and marine processing industries, and

municipal wastes (i.e., sewage and garbage), have become major sources of

environmental pollution in both developed and developing countries.

Furthermore, the production of methane from paddy fields and ruminant

animals and of carbon dioxide from the burning of fossil fuels, land clearing

and organic matter decomposition have been linked to global warming as

"greenhouse gases" (Parr and Hornick, 1992b).

Chemical-based, conventional systems of agricultural production have created

many sources of pollution that, either directly or indirectly, can contribute to

degradation of the environment and destruction of our natural resource base.

This situation would change significantly if these pollutants could be utilized in

agricultural production as sources of energy.

Therefore, it is necessary that future agricultural technologies be compatible

with the global ecosystem and with solutions to such problems in areas

different from those of conventional agricultural technologies. An area that

appears to hold the greatest promise for technological advances in crop

production, crop protection, and natural resource conservation is that of

beneficial and effective microorganisms applied as soil, plant and

environmental inoculants (Higa, 1995).

 

 

Beneficial and Effective Microorganisms for a Sustainable Agriculture

Towards Agriculture Without Chemicals and With Optimum Yields of

High Quality Crops.

 

 

Agriculture in a broad sense, is not an enterprise which leaves everything to

nature without intervention. Rather it is a human activity in which the farmer

attempts to integrate certain agro ecological factors and production inputs for

optimum crop and livestock production. Thus, it is reasonable to assume that

farmers should be interested in ways and means of controlling beneficial soil

microorganisms as an important component of the agricultural environment.

Nevertheless, this idea has often been rejected by naturalists and proponents

of nature farming and organic agriculture. They argue that beneficial soil

microorganisms will increase naturally when organic amendments are applied

to soils as carbon, energy and nutrient sources. This indeed may be true

where an abundance of organic materials are readily available for recycling

which often occurs in small-scale farming? However, in most cases, soil

microorganisms, beneficial or harmful, have often been controlled

advantageously when crops in various agro ecological zones are grown and

cultivated in proper sequence (i.e., crop rotations) and without the use of

pesticides. This would explain why scientists have long been interested in the

use of beneficial microorganisms as soil and plant inoculants to shift the

microbiological equilibrium in a way that enhances soil quality and the yield

and quality of crops (Higa and Wididana, 1991b; Higa, 1994:1995).

Most would agree that a basic rule of agriculture is to ensure that specific

crops are grown according to their agro climatic and agro ecological

requirements. However, in many cases the agricultural economy is based on

market forces that demand a stable supply of food, and thus, it becomes

necessary to use farmland to its full productive potential throughout the year.

The purpose of crop breeding is to improve crop production, crop protection,

and crop quality. Improved crop cultivars along with improved cultural and

management practices have made it possible to grow a wide variety of

agricultural and horticultural crops in areas where it once would not have been

culturally or economically feasible. The cultivation of these crops in such

diverse environments has contributed significantly to a stable food supply in

many countries. However, it is somewhat ironic that new crop cultures are

almost never selected with consideration of their nutritional quality or

bioavailability after ingestion (Hornick, 1992).

As will be discussed later, crop growth and development are closely related to

the nature of the soil micro flora, especially those in close proximity to plant

roots, i.e., the rhizosphere. Thus, it will be difficult to overcome the limitations

of conventional agricultural technologies without controlling soil

microorganisms. This particular tenet is further reinforced because the

evolution of most forms of life on earth and their environments are sustained

by microorganisms. Most biological activities are influenced by the state of

these invisible, minuscule units of life. Therefore, to significantly increase food

production, it is essential to develop crop cultivars with improved genetic

capabilities (i.e., greater yield potential, disease resistance, and nutritional

quality) and with a higher level of environmental competitiveness, particularly

under stress conditions (i.e., low rainfall, high temperatures, nutrient

deficiencies, and aggressive weed growth).

To enhance the concept of controlling and utilizing beneficial microorganisms

for crop production and protection, one must harmoniously integrate the

essential components for plant growth and yield including light (intensity,

photoperiodicity and quality), carbon dioxide, water, nutrients (organic inorganic)

soil type, and the soil micro flora. Because of these vital

interrelationships, it is possible to envision a new technology and a more

energy-efficient system of biological production.

Low agricultural production efficiency is closely related to a poor coordination

of energy conversion which, in turn, is influenced by crop physiological

factors, the environment, and other biological factors including soil

microorganisms. The soil and rhizosphere micro flora can accelerate the

growth of plants and enhance their resistance to disease and harmful insects

by producing bioactive substances. These microorganisms maintain the

growth environment of plants, and may have secondary effects on crop

quality. A wide range of results are possible depending on their predominance

and activities at any one time. Nevertheless, there is a growing consensus

that it is possible to attain maximum economic crop yields of high quality, at

higher net returns, without the application of chemical fertilizers and

pesticides. Until recently, this was not thought to be a very likely possibility

using conventional agricultural methods. However, it is important to recognize

that the best soil and crop management practices to achieve a more

sustainable agriculture will also enhance the growth, numbers and activities of

beneficial soil microorganisms that, in turn, can improve the growth, yield and

quality of crops (National Academy of Sciences, 1989; Hornick, 1992; Parr et

al., 1992).

 

 

CONTROLLING THE SOIL MICROFLORA:

PRINCIPLES AND STRATEGIES

 

 

Principles of Natural Ecosystems and the Application of Beneficial and

Effective Microorganisms

 

The misuse and excessive use of chemical fertilizers and pesticides have

often adversely affected the environment and created many a) food safety and

quality and b) human and animal health problems. Consequently, there has

been a growing interest in nature farming and organic agriculture by

consumers and environmentalists as possible alternatives to chemical-based,

conventional agriculture.

Agricultural systems which conform to the principles of natural ecosystems

are now receiving a great deal of attention in both developed and developing

countries. A number of books and journals have recently been published

which deal with many aspects of natural farming systems. New concepts such

as alternative agriculture, sustainable agriculture, soil quality, integrated pest

management, integrated nutrient management and even beneficial

microorganisms are being explored by the agricultural research establishment

(National Academy of Sciences, 1989; Reganold et al., 1990; Parr et al.,

1992). Although these concepts and associated methodologies hold

considerable promise, they also have limitations. For example, the main

limitation in using microbial inoculants is the problem of reproducibility and

lack of consistent results.

Unfortunately certain microbial cultures have been promoted by their suppliers

as being effective for controlling a wide range of soil-borne plant diseases

when in fact they were effective only on specific pathogens under very specific

conditions. Some suppliers have suggested that their particular microbial

inoculants is akin to a pesticide that would suppress the general soil microbial

population while increasing the population of a specific beneficial

microorganism. Nevertheless, most of the claims for this single-culture

microbial inoculants are greatly exaggerated and have not proven to be

effective under field conditions. One might speculate that if all of the microbial

cultures and inoculants that are available as marketed products were used

some degree of success might be achieved because of the increased diversity

of the soil micro flora and stability that is associated with mixed cultures. While

this, of course, is a hypothetical example, the fact remains that there is a

greater likelihood of controlling the soil micro flora by introducing mixed,

compatible cultures rather than single pure cultures (Higa, 1991).

Even so, the use of mixed cultures in this approach has been criticized

because it is difficult to demonstrate conclusively which microorganisms are

responsible for the observed effects, how the introduced microorganisms

interact with the indigenous species, and how these new associations affect

the soil/plant environment. Thus, the use of mixed cultures of beneficial

microorganisms as soil inoculants to enhance the growth, health, yield, and

quality of crops has not gained widespread acceptance by the agricultural

research establishment because conclusive scientific proof is often lacking.

The use of mixed cultures of beneficial microorganisms as soil inoculants is

based on the principles of natural ecosystems which are sustained by their

constituents; that is, by the quality and quantity of their inhabitants and

specific ecological parameters, i.e., the greater the diversity and number of

the inhabitants, the higher the order of their interaction and the more stable

the ecosystem. The mixed culture approach is simply an effort to apply these

principles to natural systems such as agricultural soils, and to shift the

microbiological equilibrium in favor of increased plant growth, production and

protection (Higa, 1991; 1994;Parr et al., 1994).

It is important to recognize that soils can vary tremendously as to their types

and numbers of microorganisms. These can be both beneficial and harmful to

plants and often the predominance of either one depends on the cultural and

management practices that are applied. It should also be emphasized that

most fertile and productive soils have a high content of organic matter and,

generally, have large, populations of highly diverse microorganisms (i.e., both

species and genetic diversity). Such soils will also usually have a wide ratio of

beneficial to harmful microorganisms (Higa and Wididana, 1991b).

 

 

Controlling the Soil Micro flora for Optimum Crop Production and

Protection

 

 

The idea of controlling and manipulating the soil micro flora through the use of

inoculants organic amendments and cultural and management practices to

create a more favorable soil microbiological environment for optimum crop

production and protection is not new. For almost a century, microbiologists

have known that organic wastes and residues, including animal manures, crop

residues, green manures, municipal wastes (both raw and composted),

contain their own indigenous populations of microorganisms often with broad

physiological capabilities.

It is also known that when such organic wastes and residues are applied to

soils many of these introduced microorganisms can function as bio control

agents by controlling or suppressing soil-borne plant pathogens through their

competitive and antagonistic activities. While this has been the theoretical

basis for controlling the soil micro flora, in actual practice the results have been

unpredictable and inconsistent, and the role of specific microorganisms has

not been well-defined.

For, many years’ microbiologists have tried to culture beneficial

microorganisms for use as soil inoculants to overcome the harmful effects of

phytopathogenic organisms, including bacteria, fungi and nematodes. Such

attempts have usually involved single applications of pure cultures of

microorganisms which have been largely unsuccessful for several reasons.

First, it is necessary to thoroughly understand the individual growth and

survival characteristics of each particular beneficial microorganism, including

their nutritional and environmental requirements. Second, we must

understand their ecological relationships and interactions with other

microorganisms, including their ability to coexist in mixed cultures and after

application to soils (Higa, 1991; 1994).

There are other problems and constraints that have been major obstacles to

controlling the micro flora of agricultural soils. First and foremost is the large

number of types of microorganisms that are present at any one time, their

wide range of physiological capabilities, and the dramatic fluctuations in their

populations that can result from man’s cultural and management practices

applied to a particular farming system. The diversity of the total soil micro flora

depends on the nature of the soil environment and those factors which affect

the growth and activity of each individual organism including temperature,

light, aeration, nutrients, organic matter, pH and water. While there are many

microorganisms that respond positively to these factors, or a combination

thereof, there are many that do not. Microbiologists have actually studied

relatively few of the microorganisms that exist in most agricultural soil, mainly

because we don't know how to culture them; i.e., we know very little about

their growth, nutritional, and ecological requirements.

The "diversity" and "population" factors associated with the soil micro flora

have discouraged scientists from conducting research to develop control

strategies. Many believe that, even when beneficial microorganisms are

cultured and inoculated into soils, their number is relatively small compared

with the indigenous soil inhabitants, and they would likely be rapidly

overwhelmed by the established soil micro flora. Consequently, many would

argue that even if the application of beneficial microorganisms is successful

under limited conditions (e.g., in the laboratory) it would be virtually impossible

to achieve the same success under actual field conditions. Such thinking still

exists today, and serves as a principle constraint to the concept of controlling

the soil micro flora (Higa, 1994).

It is noteworthy that most of the microorganisms encountered in any particular

soil are harmless to plants with only a relatively few that function as plant

pathogens or potential pathogens. Harmful microorganisms become dominant

if conditions develop that are favorable to their growth, activity and

reproduction. Under such conditions, soil-borne pathogens (e.g., fungal

pathogens) can rapidly increase their populations with devastating effects on

the crop. If these conditions change, the pathogen population declines just as

rapidly to its original state. Conventional farming systems that tend toward the

consecutive planting of the same crop (i.e., monoculture) necessitate the

heavy use of chemical fertilizers and pesticides. This, in turn, generally

increases the probability that harmful, disease-producing, plant pathogenic

microorganisms will become more dominant in agricultural soils (Higa, 1991;

1994; Parr and Hornick, 1994). Chemical-based conventional farming

methods are not unlike symptomatic therapy. Examples of this are applying

fertilizers when crops show symptoms of nutrient-deficiencies, and applying

pesticides whenever crops are attacked by insects and diseases. In efforts to

control the soil micro flora some scientists feel that the introduction of

beneficial microorganisms should follow a symptomatic approach. However,

we do not agree. The actual soil conditions that prevail at any point in time

may be most unfavorable to the growth and establishment of laboratory cultured,

beneficial microorganisms. To facilitate their establishment, it may

require that the farmer make certain changes in his cultural and management

practices to induce conditions that will (a) allow the growth and survival of the

inoculated microorganisms and (b) suppress the growth and activity of the

indigenous plant pathogenic microorganisms (Higa, 1994; Parr et al., 1994).

An example of the importance of controlling the soil micro flora and how

certain cultural and management practices can facilitate such control is useful

here. Vegetable cultivars are often selected on their ability to grow and

produce over a wide range of temperatures. Under cool, temperate conditions

there are generally few pest and disease problems. However, with the onset

of hot weather, there is a concomitant increase in the incidence of diseases

and insects making it rather difficult to obtain acceptable yields without

applying pesticides. With higher temperatures, the total soil microbial

population increases as does certain plant pathogens such as Fusarium,

which is one of the main putrefactive, fungal pathogens in soil. The incidence

and destructive activity of this pathogen can be greatly minimized by adopting

reduced tillage methods and by shading techniques to keep the soil cool

during hot weather. Another approach is to inoculate the soil with beneficial,

antagonistic, antibiotic-producing microorganisms such as actinomycetes and

certain fungi (Higa and Wididana, 1991a; 1991b).

 

 

Application of Beneficial and Effective Microorganisms: A New

Dimension

 

 

Many microbiologists believe that the total number of soil microorganisms can

be increased by applying organic amendments to the soil. This is generally

true because most soil microorganisms are heterotrophic, i.e., they require

complex organic molecules of carbon and nitrogen for metabolism and

biosynthesis. Whether the regular addition of organic wastes and residues will

greatly increase the number of beneficial soil microorganisms in a short period

of time is questionable. However, we do know that heavy applications of

organic materials, such as seaweed, fish meal, and chitin from crushed crab

shells, not only helps to balance the micronutrient content of a soil but also

increases the population of beneficial antibiotic-producing actinomycetes. This

changes the soil to a disease-suppressive condition within a relatively short

period.

The probability that a particular beneficial microorganism will become

predominant, even with organic farming or nature farming methods, will

depend on the ecosystem and environmental conditions. It can take several

hundred years for various species of higher and lower plants to interact and

develop into a definable and stable ecosystem. Even if the population of a

specific microorganism is increased through cultural and management

practices, whether it will be beneficial to plants is another question. Thus, the

likelihood of a beneficial, plant-associated microorganism becoming

predominant under conservation-based farming systems is virtually impossible

to predict. Moreover, it is very unlikely that the population of useful anaerobic

microorganisms, which usually comprise only a small part of the soil

micro flora, would increase significantly even under natural farming conditions.

This information then emphasizes the need to develop methods for isolating

and selecting different microorganisms for their beneficial effects on soils and

plants. The ultimate goal is to select microorganisms that are physiologically

and ecologically compatible with each other and that can be introduced as

mixed cultures into soil where their beneficial effects can be realized (Higa,

1991; 1994; 1995).

 

 

Application of Beneficial and Effective Microorganisms: Fundamental

Considerations

 

 

Microorganisms are utilized in agriculture for various purposes; as important

components of organic amendments and composts, as legume inoculants for

biological nitrogen fixation as a means of suppressing insects and plant

diseases to Improve crop quality and yields, and for reduction of labor. All of

these are closely related to each other. An important consideration in the

application of beneficial microorganisms to soils is the enhancement of their

synergistic effects. This is difficult to accomplish if these microorganisms are

applied to achieve symptomatic therapy, as in the case of chemical fertilizers

and pesticides (Higa, 1991; 1994).

If cultures of beneficial microorganisms are to be effective after inoculation

into soil, it is important that their initial populations be at a certain critical

threshold level. This helps to ensure that the amount of bioactive substances

produced by them will be sufficient to achieve the desired positive effects on

crop production and/or crop protection. If these conditions are not met, the

introduced microorganisms, no matter how useful they are, will have little if

any effect. At present, there are no chemical tests that can predict the

probability of a particular soil-inoculated microorganism to achieve a desired

result. The most reliable approach is to inoculate the beneficial microorganism

into soil as part of a mixed culture, and at a sufficiently high inoculums density

to maximize the probability of its adaptation to environmental and ecological

conditions (Higa and Wididana, 1991b; Parr et al., 1994).

The application of beneficial microorganisms to soil can help to define the

structure and establishment of natural ecosystems. The greater the diversity

of the cultivated plants that are grown and the more chemically complex the

biomass, the greater the diversity of the soil micro flora as to their types,

numbers and activities. The application of a wide range of different organic

amendments to soils can also help to ensure a greater microbial diversity. For

example, combinations of various crop residues, animal manures, green

manures, and municipal wastes applied periodically to soil will provide a

higher level of microbial diversity than when only one of these materials is

applied. The reason for this is that each of these organic materials has its own

unique indigenous micro flora which can greatly affect the resident soil

micro flora after they are applied, at least for a limited period.

 

 

CLASSIFICATION OF SOILS BASED ON THEIR MICROBIOLOGICAL

PROPERTIES

 

 

Most soils are classified on the basis of their chemical and physical properties;

little has been done to classify soils according to their physicochemical and

microbiological properties. The reason for this is that a soil's chemical and

physical properties are more readily defined and measured than their

microbiological properties. Improved soil quality is usually characterized by

increased infiltration; aeration, aggregation and organic matter content and by

decreased bulk density, compaction, and erosion and crusting. While these are

important indicators of potential soil productivity, we must give more attention

to soil biological properties because of their important relationship (though

poorly understood) to crop production, plant and animal health, environmental

quality, and food safety and quality. Research is needed to identify and

quantify reliable and predictable biological/ecological indicators of soil quality.

Possible indicators might include total species diversity or genetic diversity of

beneficial soil microorganisms as well as insects and animals (Reganold et

al., 1990; Parr et al., 1992).

The basic concept here is not to classify soils for the study of microorganisms

but for farmers to be able to control the soil micro flora so that biologically mediated

processes can improve the growth, yield, and quality of crops as

well as the tilth, fertility, and productivity of soils. The ultimate objective is to

reduce the need for chemical fertilizers and pesticides (National Academy of

Sciences, 1989; 1993).

 

Functions of Microorganisms: Putrefaction, Fermentation, and

Synthesis

 

 

Soil microorganisms can be classified into decomposer and synthetic

microorganisms. The decomposer microorganisms are subdivided into groups

that performs oxidative and fermentative decomposition. The fermentative

group is further divided into useful fermentation (simply called fermentation)

and harmful fermentation (called putrefaction). The synthetic microorganisms

can be sub-divided into groups having the physiological abilities to fix

atmospheric nitrogen into amino acids and/or carbon dioxide into simple

organic molecules through photosynthesis. Figure 1 (adapted from Higa) is a

simplified flow chart of organic matter transformations by soil microorganisms

that can lead to the development of disease-inducing, disease-suppressive,

zymogenic, or synthetic soils.

Fermentation is an anaerobic process by which facultative microorganisms

(e.g., yeasts) transform complex organic molecules (e.g., carbohydrates) into

simple organic compounds that often can be absorbed directly by plants.

Fermentation yields a relatively small amount of energy compared with

aerobic decomposition of the same substrate by the same group of

microorganisms. Aerobic decomposition results in complete oxidation of a

substrate and the release of large amounts of energy, gas, and heat with

carbon dioxide and water as the end products. Putrefaction is the process by

which facultative heterotrophic microorganisms decompose proteins

anaerobically, yielding malodorous incompletely oxidized, metabolites (e.g.,

ammonia, mercaptans and indole) that is often toxic to plants and animals.

The term "synthesis" as used here refers to the biosynthetic capacity of

certain microorganisms to derive metabolic energy by "fixing" atmospheric

nitrogen and/or carbon dioxide. In this context we refer to these as "synthetic"

microorganisms, and if they should become a predominant part of the soil

micro flora, then the soil would be termed a "synthetic" soil.

Nitrogen-fixing microorganisms are highly diverse, ranging from "free-living"

autotrophic bacteria of the genus Azotobacter to symbiotic, heterotrophic

bacteria of the genus Rhizobium, and blue-green algae (now mainly classified

as blue-green bacteria), all of which function aerobically. Photosynthetic

microorganisms fix atmospheric carbon dioxide in a manner similar to that of

green plants. They are also highly diverse, ranging from blue-green algae to

green algae that perform complete photosynthesis aerobically to

photosynthetic bacteria which perform incomplete photosynthesis

anaerobically.

 

 

 

Relationships Between Putrefaction, Fermentation, and Synthesis

 

The processes of putrefaction, fermentation, and synthesis proceed

simultaneously according to the appropriate types and numbers of

microorganisms that is present in the soil. The impact on soil quality

attributes and related soil properties is determined by the dominant process.

The production of organic substances by microorganisms results from the

intake of positive ions, while decomposition serves to release these positive

ions. Hydrogen ions play a pivotal role in these processes. A problem occurs

when hydrogen ions do not recombine with oxygen to form water but are

utilized to produce methane, hydrogen sulfide, ammonia, mercaptans and

other highly reduced putrefactive substances most of which are toxic to plants

and produce malodors. If a soil is able to absorb the excess hydrogen ions

during periods of soil anaerobiosis and if synthetic microorganisms such as

photosynthetic bacteria are present, they will utilize these putrefactive

substances and produce useful substrates from them which helps to maintain

a healthy and productive soil.

The photosynthetic bacteria, which perform incomplete photosynthesis

anaerobically, are highly desirable, beneficial soil microorganisms because

they are able to detoxify soils by transforming reduced, putrefactive

substances such as hydrogen sulfide into useful substrates. This helps to

ensure efficient utilization of organic matter and to improve soil fertility.

Photosynthesis involves the photo-catalyzed splitting of water which yields

molecular oxygen as a by-product. Thus, these microorganisms help to

provide a vital source of oxygen to plant roots.

Reduced compounds such as methane and hydrogen sulfide are often

produced when organic materials are decomposed under anaerobic

conditions. These compounds are toxic and can greatly suppress the activities

of nitrogen-fixing microorganisms. However, if synthetic microorganisms, such

as photosynthetic bacteria that utilize reduced substances, are present in the

soil, oxygen deficiencies are not likely to occur. Thus, nitrogen-fixing

microorganisms, coexisting in the soil with photosynthetic bacteria, can

function effectively in fixing atmospheric nitrogen even under anaerobic

conditions.

Photosynthetic bacteria not only perform photosynthesis but can also fix nitrogen.

Moreover, it has been shown that, when they coexist, in soil with

species of Azotobacter, their ability to fix nitrogen is enhanced. This then is an

example of a synthetic soil. It also suggests that by recognizing the role,

function, and mutual compatibility of these two bacteria and utilizing them

effectively to their full potential, soils can be induced to a greater synthetic

capacity. Perhaps the most effective synthetic soil system results from the

enhancement of zymogenic and synthetic microorganisms; this allows

fermentation to become dominant over putrefaction and useful synthetic

processes to proceed.

 

 

Classification of Soils Based on the Functions of Microorganisms

 

 

As discussed earlier (Figure 1), soils can be characterized according to their

indigenous micro flora which perform putrefactive, fermentative, synthetic and

zymogenic reactions and processes. In most soils, these three functions are

going on simultaneously with the rate and extent of each determined by the

types and numbers of associated microorganisms that are actively involved at

any one time.

A simple diagram showing a classification of soils based on the activities and

functions of their predominant microorganisms are presented in Fig. 2.

 

 

Disease-Inducing Soils.

 

 

In this type of soil, plant pathogenic microorganisms

such as Fusarium fungi can comprise 5 to 20 percent of the total micro flora if

fresh organic matter with high nitrogen content is applied to such a soil,

incompletely oxidized products can arise that are malodorous and toxic to

growing plants. Such soils tend to cause frequent infestations of disease

organisms, and harmful insects. Thus, the application of fresh organic matter

to these soils is often harmful to crops. Probably more than 90 percent of the

agricultural land devoted to crop production worldwide can be classified as

having disease-inducing soil. Such soils generally have poor physical

properties, and large amounts of energy are lost as "greenhouse" gases,

particularly in the case of rice fields. Plant nutrients are also subject to

immobilization into unavailable forms.

 

 

Disease-Suppressive Soils.

 

 

The micro flora of disease-suppressive soils is

usually dominated by antagonistic microorganisms that produce copious

amounts of antibiotics. These include fungi of the genera Penicillium,

Trichoderma, and Aspergillus, and actinomycetes of the genus Streptomyces.

The antibiotics they produce can have biostatic and biocidal effects on soil borne

plant pathogens, including Fusarium which would have an incidence in

these soils of less than 5 percent. Crops planted in these soils are rarely

affected by diseases or insect pests. Even if fresh organic matter with a high

nitrogen content is applied, the production of putrescent substances is very

low and the soil has a pleasant earthy odor after the organic matter is

decomposed. These soils generally have excellent physical properties; for

example, they readily, form water-stable aggregates and they are well aerated,

and have a high permeability to both air and water. Crop yields in the

disease-suppressive soils are often slightly lower than those in synthetic soils.

Highly acceptable crop yields are obtained whenever a soil has a

predominance of both disease-suppressive and synthetic microorganisms.

 

 

Zymogenic Soils.

 

 

These soils are dominated by a micro flora that can perform

useful kinds of fermentations, i.e., the breakdown of complex organic

molecules into simple organic substances and inorganic materials. The

organisms can be either obligate or facultative anaerobes. Such fermentation producing

microorganisms often comprise the micro flora of various organic

materials, i.e., crop residues, animal manures, green manures and municipal

wastes including composts. After these amendments are applied to the soil,

their number: and fermentative activities can increase dramatically and

overwhelm the indigenous soil micro flora for an indefinite period. While these

microorganisms remain predominant, the soil can be classified as a

zymogenic soil which is generally characterized by a) pleasant, fermentative

odors especially after tillage, b) favorable soil physical properties (e.g.,

Increased aggregate stability, permeability, aeration and decreased resistance

to tillage c) large amounts of inorganic nutrients, amino acids, carbohydrates,

vitamins and other bioactive substances which can directly or indirectly

enhance the growth, yield and quality of crops, d) low occupancy of Fusarium

fungi which is usually less than 5 percent, and e) low production of

greenhouse gases (e.g., methane, ammonia, and carbon dioxide) from

croplands, even where flooded rice is grown.

 

 

Synthetic Soils.

 

 

These soils contain significant populations of

microorganisms which are able to fix atmospheric nitrogen and carbon dioxide

into complex molecules such as amino acids, proteins and carbohydrates.

Such microorganisms include photosynthetic bacteria which perform

incomplete photosynthesis anaerobically, certain Phycomycetes (fungi that

resemble algae), and both green algae and blue--green algae which function

aerobically. All of these are photosynthetic organisms that fix atmospheric

nitrogen. If the water content of these soils is stable, their fertility can be

largely maintained by regular additions of only small amounts of organic

materials. These soils have a low Fusarium occupancy and they are often of

the disease-suppressive type. The production of gases from fields where

synthetic soils are present is minimal, even for flooded rice.

This is a somewhat simplistic classification of soils based on the functions of

their predominant types of microorganisms, and whether they are potentially

beneficial or harmful to the growth and yield of crops. While these different

types of soils are described here in a rather idealized manner, the fact is that

in nature they are not always clearly defined because they often tend to have

some of the same characteristics. Nevertheless, research has shown that a

disease-inducing soil can be transformed into disease-suppressing,

zymogenic and synthetic soils by inoculating the problem soil with mixed

cultures of effective microorganisms (Higa, 1991; 1994; Parr et al., 1994).

Thus it is somewhat obvious that the most desirable agricultural soil for

optimum growth, production, protection, and quality of crops would be the

composite soil indicated in Fig. 2, i.e., a soil that is highly zymogenic and

synthetic, and has an established disease-suppressive capacity. This then is

the principle reason for seeking ways and means of controlling the micro flora

of agricultural soils.

 

 

SUMMARY AND CONCLUSIONS

 

 

Controlling the soil micro flora to enhance the predominance of beneficial and

effective microorganisms can help to improve and maintain the soil chemical

and physical properties. The proper and regular addition of organic

amendments are often an important part of any strategy to exercise such

control.

Previous efforts to significantly change the indigenous micro flora of a soil by

introducing single cultures of extrinsic microorganisms have largely been

unsuccessful. Even when a beneficial microorganism is isolated from a soil,

cultured in the laboratory, and re-inoculated into the same soil at a very high

population, it is immediately subject to competitive and antagonistic effects

from the indigenous soil micro flora and its numbers soon decline. Thus, the

probability of shifting the "microbiological equilibrium" of a soil and controlling

it to favor the growth, yield and health of crops is much greater if mixed

cultures of beneficial and effective microorganisms are introduced that are

physiologically and ecologically compatible with one another. When these

mixed cultures become established their individual beneficial effects are often

magnified in a synergistic manner.

Actually, a disease-suppressive micro flora can be developed rather easily by

selecting and culturing certain types of gram-positive bacteria that produces

antibiotics and have a wide range of specific functions and capabilities; these

organisms include facultative anaerobes, obligate aerobes, acidophilic and

alkalophilic microbes. These microorganisms can be grown to high

populations in a medium consisting of rice bran, oil cake and fish meal and

then applied to soil along with well-cured compost that also has a large stable

population of beneficial microorganisms, especially facultative anaerobic

bacteria. A soil can be readily transformed into a zymogenic/synthetic soil with

disease-suppressive potential if mixed cultures of effective microorganisms

with the ability to transmit these properties are applied to that soil.

The desired effects from applying cultured beneficial and effective

microorganisms to soils can be somewhat variable, at least initially. In some

soils, a single application (i.e., inoculation) may be enough to produce the

expected results, while for other soils even repeated applications may appear

to be ineffective. The reason for this is that in some soils it takes longer for the

introduced microorganisms to adapt to a new set of ecological and

environmental conditions and to become well-established as a stable,

effective and predominant part of the indigenous soil micro flora. The important

consideration here is the careful selection of a mixed culture of compatible,

effective microorganisms properly cultured and provided with acceptable

organic substrates. Assuming that repeated applications are made at regular

intervals during the first cropping season, there is a very high probability that

the desired results will be achieved.

There are no meaningful or reliable tests for monitoring the establishment of

mixed cultures of beneficial and effective microorganisms after application to a

soil. The desired effects appear only after they are established and become

dominant, and remain stable and active in the soil. The inoculum densities of

the mixed cultures and the frequency of application serve only as guidelines to

enhance the probability of early establishment. Repeated applications,

especially during the first cropping season, can markedly facilitate early

establishment of the introduced effective microorganisms.

Once the "new" micro flora is established and stabilized, the desired effects

will continue indefinitely and no further applications are necessary unless

organic amendments cease to be applied, or the soil is subjected to severe

drought or flooding.

Finally, it is far more likely that the micro flora of a soil can be controlled

through the application of mixed cultures of selected beneficial and effective

microorganisms than by the use of single or pure cultures. If the

microorganisms comprising the mixed culture can coexist and are

physiologically compatible and mutually complementary, and if the initial

inoculum density is sufficiently high, there is a high probability that these

microorganisms will become established in the soil and will be effective as an

associative group, whereby such positive interactions would continue. If so,

then it is also highly, probable that they will exercise considerable control over

the indigenous soil micro flora which, in due course, would likely be

transformed into or replaced by a "new" soil micro flora.

 

REFERENCES

 

Higa, T. 1991. Effective microorganisms: A biotechnology for mankind. p.8-14.

In J.F. Parr, S.B. Hornick, and C.E. Whitman (ed.) Proceedings of the First

International Conference on Kyusei Nature Farming. U.S. Department of

Agriculture, Washington, D.C., USA.

Higa, T. and G.N. Wididana 1991a. The concept and theories of effective

microorganisms. p. 118-124. In Parr, S.B. Hornick, and C.E. Whitman (ed.)

Proceedings of the First International Conference on Kyusei Nature Farming.

U.S. Department of Agriculture, Washington, D.C., USA.

Higa, T. and G.N. Wididana 199lb. Changes In the soil micro flora Induced by

effective microorganisms. p.153-162. In J.F. Parr, S.B. Hornick, and C.E.

Whitman (ed.) Proceedings of the First International Conference on Kyusei

Nature Farming. U.S. Department of Agriculture, Washington, D.C., USA.

Higa, T. 1994. Effective Microorganisms: A New Dimension for Nature

Farming. p. 20-22. In J.F. Parr, S.B. Hornick, and M.E. Simpson (ed.)

Proceedings of the Second International Conference on Kyusei Nature

Farming. U.S. Department of Agriculture, Washington, D.C, USA.

Higa, T. 1995. Effective microorganisms: Their role in Kyusei Nature Farming

and sustainable agriculture. In J.F. Parr, S.B. Hornick, and M.E. Simpson (ed.)

Proceedings of the Third International Conference on Kyusei Nature Farming.

U.S. Department of Agriculture, Washington, D.C., USA. (In Press).

Hornick, S.B. 1992. Factors affecting the nutritional quality of crops. Amer. J.

Alternative Agric. 7:63-68.

National Academy of Sciences. 1989. Alternative Agriculture. Committee on

the Role of Alternative Agriculture Farming Methods in Modern Production

Agriculture. National Research Council, Board on Agriculture. National

Academy Press, Washington, D.C., USA. 448 p.

National Academy of Sciences. 1993. Pesticides in Diets of Infants and

Children National Research Council, Board on Agriculture. National Academy

Press, Washington, D.C., USA. 373 p.

Parr, J.F. and S.B. Hornick 1992a. Agricultural use of organic amendments: A

historical perspective. Amer. J. Alternative Agric. 7:181-189.

Parr, J.F. and S.B. Hornick. 1992b. Utilization of municipal wastes. p.545-559.

In F.B. Metting (ed.) Soil Microbial Ecology: Applications in Agriculture and

Environmental Management. Marcel Dekker, Inc., New York, USA.

Parr, J.F., R.I. Papendick, S.B. Hornick, and R.E. Meyer. 1992. Soil quality:

Attributes and relationship to alternative and sustainable agriculture. Amer. J.

Alternative Agric. 7:5-11.

Parr, J.F. and S.B. Hornick. 1994. Assessment of the Third International

Conference on Kyusei Nature Farming: Round Table Discussion by USDA

Scientists, October 7, 1993. Published by the Nature Farming Research and

Development Foundation, Lompoc, California, USA.

Parr, J.F., S.B. Hornick, and D.D. Kaufman. 1994. Use of microbial Inoculants

and organic fertilizers in agricultural production. In Proceedings of the

International Seminar on the Use of Microbial and Organic Fertilizers in

Agricultural Production. Published by the Food and Fertilizer Technology

Center, Taipei, Taiwan.

Reganold, J.P., R.I Papendick, and J.F. Parr. 1990. Sustainable Agriculture.

Scientific American 262(6): 112-120.

 

Table 1.

Some Common Functions of Beneficial and Harmful Soil

Microorganisms

as they Affect Soil Quality, Crop Production, and Plant Health.

 

Functions of Beneficial Microorganisms

 
  

  

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