# Manipulating soil microorganisms for sustainable agriculture

Ajeet Kumar, C.K. Jha

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Ajeet Kumar, C.K. Jha. Manipulating soil microorganisms for sustainable agriculture. 2021, 978-81-953069-9-2. hal-04881385

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Dr. Aneeta Yadav: Presently working as Assistant Professor and Dean (Acting), Faculty of Agricultural Sciences and Allied Industries, RAMA University, Kanpur. She also pursued her Masters' and Ph.D. in Genetics and Plant Breeding from G.B.P.U.A.T., Pantnagar. She has qualified ICAR-ASRB NET examination. Dr. Yadav has published more than 15 full length research papers, 25 abstracts, 25 Seminars/ Workshops/ Conferences/Summer School at National / International level.

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Dr. Atul Yadav: Present time he work as a Assistant Professor, Horticulture in Rama University, Kanpur, U.P. He qualified ASRB-NET (Fruit Science) in 2019. He has published 2 National Awards, 10 Research papers, 4 Books, 5 popular articles and solo author or co-author in reputed Journals and magazines.

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Dr. Ajeet Kumar: Present time he work as an Assistant Professor-cum-Scientist, Department of Soil Science, S.R.I., Dr. Rajendra Prasad Central Agricultural University Pusa (Samastipur)-848125, Bihar, India, has 13 years of teaching, research and extension experiences. Dr. Kumar, Ph.D. (B.H.U., Varanasi), FHAS; He has 186 scientific contributions, 65 research papers, 52 popular articles, 08 chapters in books, 04 books, 24 research / extension bulletins and 02 edited publications.

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Madhukar Singh: Mr. Singh, born on 24th July 1994 Pithani Bilhaur Kanpur Nagar. He completed graduation in 2014 from S.V.P. University of Agriculture and Technology, Meerut, Uttar Pradesh. He obtained Master degree in Crop Physiology from A.N.D.U.A&T, Fazabad in 2016. Presently he is pursuing in Ph.D. Crop Physiology from Chandra Shekhar Azad University of Agriculture & Technology Kanpur, Uttar Pradesh. Mr. Singh has 5 Research Papers, 2 National and 1 International Awards and solo author or co-author in reputed Journals and magazines.

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Mr. Abhinav Yadav: has completed his M.Sc from Narendra Dev university of Agricultural & Technology, Kumarganj, Fazabad under the guidance of Dr. ShivaNath. Presently he is working as Project Associate at CSIR-NBRI, Lucknow. He has published 2 National Awards, 2 Research papers, 5 popular articles and solo author or co-author in reputed Journals and magazines.

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Learning Media
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Learning Media Publication
A-16, Aman Vihar, Mawana Road,
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Contact No. +918791976106
E-mail:learningmediapublicationmeerut@gmail.com
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Yourbookchapter.com

# Plant Science

Anita Yadav

Atul Yadav

Ajeet Kumar

Madhukar Singh

Abhinav Yadav

## Recent Innovation in Agriculture Sectors

2021

2021

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978-81-953069-9-2

This Book Content 200 pages only

2021
Plant Science

First Edition: 2021

ISBN: 978-81-953069-9-2

Copyright © Authors

**Disclaimer:** The authors are solely responsible for the contents of the book chapters compiled in this book. The editors or publisher do not take any, responsibility for same in any manner. Errors, if any, are purely unintentional and readers are requested to communicate such errors to the editors or publisher to avoid discrepancies in future.

Printed & Published by:

Learning Media Publication
A-16, Aman Vihar, Mawana Road,
Opp. J.P. Academy, Meerut-250001
Contact No. +918791976106
E-mail: learningmediapublicationmeerut@gmail.com
Website: www-learningmedia.in
**Editors**

**Dr. Aneeta Yadav**

Associate Professor cum Dean,
Department of Genetical and Plant Breeding
Rama University, Kanpur, Uttar Pradesh, India

**Dr. Atul Yadav**

Assistant Professor,
Department of Horticulture,
Rama University, Kanpur, Uttar Pradesh, India

**Mr. Ajeet Kumar**

Assistant Professor-cum-Scientist,
Department of Soil Science, Sugarcane Research Institute,
Dr. Rajendra Prasad Central Agricultural University Pusa, Bihar, India

**Mr. Madhukar Singh**

Research Scholar,
Crop Physiology,
Chandra Shekhar Azad University of Agriculture & Technology Kanpur
Uttar Pradesh, India

**Mr. Abhinav Yadav**

Project Associate,
CSIR-National Botanical Research Institute, Lucknow, Uttar Pradesh, India

**Learning Media Publication**

Meerut, Uttar Pradesh, India
Content

<table><thead><tr><td>S. No.</td><td>Title with Author Name</td><td>Page No.</td></tr></thead><tbody><tr><td>1.</td><td>Introduction to Bee and Beekeeping<br/>Author: M.P. Gautam, Akhilesh Kumar Yadav and Nagendra Kumar</td><td>5-9</td></tr><tr><td>2.</td><td>Product Collected and Modified by Bees, Marketing Economics and Development Programmes.<br/>Author: Nagendra Kumar, Akhilesh Kumar Yadav and M.P. Gautam</td><td>10-18</td></tr><tr><td>3.</td><td>Weed Management Practices of Horticultural Crops<br/>Author: Abhinav Kumar, Arun Kumar Singh and Archana Singh</td><td>19-27</td></tr><tr><td>4.</td><td>Roles and Importance of Microbiology in Horticulture<br/>Author: Gayatri Singh et al.</td><td>28-49</td></tr><tr><td>5.</td><td>Apiculture<br/>Author: Sushant Kumar et al.</td><td>50-65</td></tr><tr><td>6.</td><td>Cultivation Practices of Statice Flower<br/>Author: Dhan Singh et al.</td><td>66-69</td></tr><tr><td>7.</td><td>Dry Land Agriculture in India<br/>Author: Ranjeet Singh Bochalya et al.</td><td>70-77</td></tr><tr><td>8.</td><td>Organic Farming for Climate Resilience<br/>Author: Smita Singh et al.</td><td>78-85</td></tr><tr><td>9.</td><td>Concept and Methods of Hybrids Seed Production of Vegetable Crops<br/>Author: Suhel Mehandi</td><td>86-94</td></tr><tr><td>10.</td><td>Insecticidal and Chemical Profiles of Essential Oil Mentha Spp.<br/>Author: Aditya Patel</td><td>95-102</td></tr><tr><td>11.</td><td>Manupulating Soil Microorganisms for Sustainable Agriculture<br/>Author: Ajeet Kumar and C.K. Jha</td><td>103-117</td></tr><tr><td>12.</td><td>Pre-Breeding Approaches and Prospects for Crop Improvement<br/>Author: Ashok Kumar</td><td>118-126</td></tr><tr><td>13.</td><td>Role of Microbial Insecticides in Insect Pest Management<br/>Author: Pawan Kumar</td><td>127-138</td></tr><tr><td>14.</td><td>Soil Conservation<br/>Author: Ankit Gupta and Hariom Mishra</td><td>139-149</td></tr><tr><td>15.</td><td>Organic Farming<br/>Author: Hariom Mishra and Ankit Gupta</td><td>150-155</td></tr><tr><td>16.</td><td>Role of Heterosis Breeding in Crop Improvement<br/>Author: Ashok Kumar</td><td>156-169</td></tr><tr><td>17.</td><td>Effect of Climate Change on Indian Agriculture<br/>Author: Raghvendra Kumar Aryan et al.</td><td>170-176</td></tr><tr><td>18.</td><td>Support to Women Farmers Through Government Schemes<br/>Author: Dr. Abha Singh et al.</td><td>177-182</td></tr></tbody></table>
<table><tr><td>19.</td><td>Soil Sustainability Through Introduction of Legumes in Sugarcane<br><b>Author:</b> Dr. C.K. Jha <i>et al.</i></td><td>183-192</td></tr><tr><td>20.</td><td>Soil Pedology<br>Devesh Pathak and Poornendra Mishra</td><td>193-199</td></tr></table>
# MANUPULATING SOIL MICROORGANISMS FOR SUSTAINABLE AGRICULTURE

Ajeet Kumar and C.K. Jha

Assistant Professor-cum-Scientist, Department of Soil Science, Sugarcane Research Institute, DRPCAU, Pusa (Samastipur)-848125, Bihar, India

## 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 for food processing, agricultural biotechnology, and more effective treatment of agricultural and municipal wastes provide a most impressive record of achievement.

Microbial technologies have been applied to various agricultural 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 (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. 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). For many years, soil microbiologists have tended to differentiate soil microorganisms as beneficial or harmful according to their functions and how they affect soil quality, plant growth & yield, and plant health. 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.

This Chapter presents new perspectives on the role and application of beneficial microorganism, as microbial inoculants for shifting the soil microbiological equilibrium in such a ways that can improve soil quality, enhance crop production and protection, conserve natural resources, and ultimately create a more sustainable agriculture and environment. The strategies will deal here that how beneficial microorganisms can be more effective after inoculation into soils.

## The Concept of Effective Microorganisms

The effective microorganism consists of mixed cultures of beneficial naturally-occurring microorganisms that can be applied as inoculants to increase the microbial diversity of soils and plant. Several results of research has shown that the inoculation of effective microorganism cultures to the soil/plant ecosystem can improve soil quality, soil health, and the growth, yield, and quality of crops. The effective microorganism 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. Effective microorganism 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.

Effective microorganism designates a large group of often unknown or ill-defined microorganisms that interact favorably in soils and with plants to render beneficial effects. The term "effective microorganisms" denote specific mixed cultures of known, beneficial microorganisms that are being used effectively as microbial inoculants.

## Utilization of Beneficial Microorganisms In Agriculture

Conceptual design is important in developing new technologies for utilizing beneficial and effective microorganisms for a more sustainable agriculture. The basis of a conceptual design is implying to first conceive an ideal 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. An ideal agricultural system is an idealized system which produces food on a long-term sustainable basis.
## Efficient Utilization and Recycling of Energy

Agricultural production begins with the process of photosynthesis by green plants which require solar energy, water, and CO2. The plants utilize solar energy in fixing atmospheric carbon into carbohydrates. The energy obtained is used for biosynthesis in the plant, including essential amino acids and proteins. The materials used for agricultural production are 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 sugarcane 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.

## Conservation of Natural Resources

The excessive erosion of topsoil from farmland caused by intensive tillage has exaggerated extensive soil degradation and also contributed to the pollution of surface and groundwater. Organic wastes from animal production & agricultural, and municipal
wastes (i.e., sewage and garbage), have major sources of pollution. 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".

Chemical based agricultural production has created many sources of pollution, either directly or indirectly, can contribute to degradation of 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 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.

## Effective Microorganisms for a Sustainable Agriculture

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 production. Thus, it is assuming that farmers should be interested in ways and means of controlling beneficial soil microorganisms as an important component of the agricultural. 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, 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. Scientists have 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.

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.
The crop growth and development are closely related to the nature of the soil micro flora, especially those in close proximity to 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 of plants, and may have secondary effects on crop quality. 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.

# CONTROLLING THE SOIL MICROFLORA: PRINCIPLES AND STRATEGIES

## Principles of Natural Ecosystems and the Application of Beneficial Microorganisms

The 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 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. 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 (Reganold et al., 1990). Although these
concepts hold considerable promise, they also have limitations, e.g., Using microbial inoculants have 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 inoculant 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 these 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. In fact, there is a greater likelihood of controlling the soil micro flora by introducing mixed, compatible cultures rather than single pure cultures (Higa, 1991). 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 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 of no conclusive scientific proof. The use of mixed culture of beneficial microorganisms as soil inoculants is based on the principles of natural ecosystems which is sustained 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 favour of increased plant growth, production and protection.

Soils vary tremendously to their types and numbers of microorganism's presents. 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 emphasized that most fertile and productive soils have a high content of organic matter and generally, have large, population of highly diverse microorganisms. Such soils usually have a wide ratio of beneficial to harmful microorganisms.

## Soil Micro flora for Optimum Crop Production and Protection

The idea of manipulating the soil micro flora through the use of inoculants organic amendments and cultural & management practices to create a more favourable soil microbiological environment for optimum crop production and protection is not new. Microbiologists have known that organic wastes and residues, including animal
manures, crop residues, green manures, municipal wastes, 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.

Microbiologists have tried to culture beneficial microorganisms for use as soil inoculants to overcome the harmful effects of phyto-pathogenic 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 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 soil. There are other problems 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 and those factors which affect the growth and activity of individual organism including temperature, light, aeration, nutrients, organic matter, pH and water. There are many microorganisms that respond positively to these factors. Microbiologists have actually studied few of the microorganisms that exist in agricultural soil, mainly because we don't know how to culture them.

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, if the application of beneficial microorganisms is successful under laboratory conditions, it would be virtually impossible to achieve the same success under field conditions.

It is noteworthy that most of the microorganisms encountered in any 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 favourable to their growth 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. 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 generally increases the probability that disease-producing, plant pathogenic microorganisms will become more dominant in agricultural soils (Parr and Hornick, 1994). Chemical-based 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, scientists feel that the introduction of beneficial microorganisms should follow a symptomatic approach. 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.

A New paradigm of Beneficial and Effective Microorganisms

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. The regular addition of organic wastes and residues greatly increase the number of beneficial soil microorganisms in a short period of time. The heavy applications of organic materials, such as seaweed, fish meal, and chitin from crushed crab shells, helps to balance the micronutrient content of a soil and also increases the population of antibiotic-producing actinomycetes. This changes the soil to a disease-suppressive condition.

The probability of particular beneficial microorganism will predominant, even with natural farming methods, will depend on the ecosystem and environmental conditions. The population of a specific microorganism is increased through cultural and management practices will be beneficial to plants. Thus, the likelihood of a beneficial, plant-associated microorganism becoming predominant under conservation-based farming systems. Moreover, 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 emphasizes the need to develop methods for isolating and selecting different microorganisms that are physiologically and ecologically compatible with each other, for introduction as mixed cultures into soil and plants, where their beneficial effects can be realized.
## Fundamental Considerations for Application of Beneficial Microorganisms

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 labour cost. 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. The 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. The number of bioactive substances produced by them will be sufficient to achieve the desired positive effects on crop production and crop protection. The most reliable approach is to inoculate the beneficial microorganism into soil as part of a mixed culture, and at a sufficiently high inoculum density to maximize the probability of its adaptation to environmental and ecological conditions.

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 and the more chemically complex the biomass, greater the diversity of the soil micro flora as to their types, numbers and activities. The application of wide range of organic amendments to soils can 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. Each of these organic materials has its own unique indigenous micro floras which greatly affect the resident soil micro flora.

## Soils Classification Based on 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 physico-chemical and microbiological properties. The reason is that a soil's chemical and physical properties are 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, erosion and crusting. These are important indicators of soil productivity; attention must be given to soil biological properties because of their important relationship to crop production, plant and animal health, 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 (Parr et al., 1992). The basic concept is 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.

## 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 perform 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. 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 are 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 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 are 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 malodours. 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 help 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. They coexist, in soil with species of *Azotobacter*, their ability to fix nitrogen is enhanced. 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. 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.

## Soil Classification Based on the Functions of Microorganism

Soils can be characterized according to their indigenous micro flora which performs 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 time.

## Disease-Inducing Soils

In this type of soil, plant pathogenic microorganisms such as *Fusarium* fungi can comprise 5 to 20 % of the total micro flora if fresh organic matter with a high nitrogen content is applied to such soil, incompletely oxidized products can arise that are odorous
and toxic to growing plants. Such soils tend to cause frequent infestations of disease, and harmful insects. Thus, the application of fresh organic matter to the soils is often harmful to crops. More than 90 percent of the agricultural land devoted to crop production 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.

## 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 bio-cidal effects on soil-borne plant pathogens, including *Fusarium* which would have an incidence in these soils of less than 5 %. Crops planted in these soils are rarely affected by diseases or insect pests. Even if fresh organic matter with 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. After the application of various organic materials 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 odours especially after tillage, b) favourable 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 %, 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 population 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 gas from fields where synthetic soils are present is minimal, even for flooded rice.

This is 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. 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. Thus, it is obvious that the most desirable agricultural soil for optimum growth, production, protection, and quality of crops would be the composite soil (a soil that is highly zymogenic and synthetic, and has an established disease-suppressive capacity). This is the principal reason for seeking ways and means of controlling the micro flora of agricultural soils.

## Summary

Controlling the soil micro flora to enhance the predominance of beneficial microorganisms can help to improve and maintain the soil chemical and physical properties. The proper addition of organic amendments is often an important 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 to favour 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 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 produce 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. 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 of cultured microorganisms to soils can be variable initially. In some soils, a single 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 careful selection of a mixed culture of compatible, effective microorganisms properly cultured and provided with acceptable organic substrates. The repeated applications 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 reliable tests for monitoring the establishment of mixed cultures of microorganisms after application into 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 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.

Conclusions

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. The microorganisms comprising the mixed culture can coexist and are physiologically compatible and mutually complementary, and 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. It is highly, probable that they will exercise considerable control over the indigenous soil microflora which, in due course, would likely be transformed into or replaced by a new soil micro flora.

References

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