Biofertilizers in Sustainable Agriculture
A C Gaur (Former) Professor and Head Division of Microbiology Indian Agricultural Research Institute, New Delhi 110 012
A ECAl
DIRECTORATE OF KNOWLEDGE MANAGEMENT IN AGRICULTURE INDIAN COUNCIL OF AGRICULTURAL RESEARCH NEW DELHI
Printed First Reprint Second Reprint
Project Director (DKMA)
Incharge, English Editorial Unit Editing
Chief Production Officer Asstt. Chief Technical Officer Senior Artist
July 2006 January 2010 June 2014
Dr Rameshwar Singh Dr Aruna T Kumar Dr Sudhir Pradhan Dr V K Bharti Kulbhushan Gupta Narendra Bahadur
All rights reserved Š 2014, Indian Council of Agricultural Research, New Delhi
ISBN : 81-7164-060-5
Price : ? 500.00
Published by Dr Rameshwar Singh, Project Director, Directorate of Knowledge Management in Agriculture, Indian Council of Agricultural Research, Krishi Anusandhan Bhavan I, Pusa, New Delhi 110 012. Printed at M/s Chandu Press, D-97, Shakarpur, Delhi-110 092
Ur
Contents Foreword
iii
Preface
v
Chapter
1
Introduction
Chapter
2
Symbiotic nitrogenous biofertilizer
38
Chapter
3
Azolla acts as green manure and production technology
93
Chapter
4
Frankia non-leguminous symbiosis
108
Chapter
5
Free living nitrogen-fixing bacteria
114
Chapter
6
Azospirillum as biofertilizer
131
Chapter
7
Blue-green algae as biofertilizer
148
Chapter
8
Phosphate solubilizing microorganisms as biofertilizer
157
Chapter
9
Mycorrhizae as biofertilizer
188
Chapter
10
Organo-biofertiltzer
213
Development of biofertilizer industry
266
Media and Methods
278
Chapter Appendix
I
283
Subject index
•vii *
1
Introduction
'
Tndian agriculture has an era of science and technology and market oriented economy Afrom the subsistence agriculture. There has been a record production of food grains of about 220 million tonne during 2003-04 showing also record levels of greater than 70.6 million tonne in wheat and 84.5 million tonne in rice production. India is first in fruit (71 million tonne) and milk (68.6 million tonne) production, and second in vegetable production (71 million tonne) in the world. The production of cash crops viz. potato, sugarcane, cotton and poultry and inland fisheries is also comfortable. There is a major gap in the demand and supply of pulses in the country. Pulse crops viz. chickpea has suffered from competition that of wheat and pushed to infertile soils. India is still spending millions of rupees in import of vegetable oil. It is estimated that oilseeds production may be more than 25-million tonne during 2003-04 likely to higher than that of the last year’s output. The output of groundnut, mustard and soybean is expected to rise. The hybrid and low input sustainable agriculture (LISA) technologies for pulses and oilseed production have a great scope in irrigated areas. Soil and water management for increasing the production in rainfed areas is a long-term goal. By 2006, the population is expected to rise to 1094.1 millions with a growth rate of 1.55% (IASRI—ICAR, 1998) whereas the food production at present is about 220 million tonne annually. To keep up with changing human needs, the food grain production has to be raised to 240 million tonnes within a short span from now. The most outstanding contradiction related to food grain problem lies in continuous population growth and continuous decline in cultivated land. There is thus ever increasing human pressure (land : human ratio) on agricultural land. The consumption of chemical fertilizers was recorded more than 14.31 million tonne during 2003-04. Plant nutrient consumption is only 79 kg/ha in India as compared to 544 kg/ha in Netherlands, 403 kg/ha in Japan, 309 kg/ha in China, and 93 kg/ha in Brazil. India has to go a long way to increase the fertilizer consumption to produce sufficient food grains to meet the food security and nutritional needs of the growing population. Rice-wheat cropping system is the major consumer of chemical fertilizers but trends of fertilizer use efficiency are not encouraging. Rice-wheat cropping is the most common and widely adopted cropping system throughout Indo-gangetic plains region. Reports of stagnation in the productivity of these crops with possible deterioration in soil ecosystem, have raised doubts on the sustainability of this important production system. A decline in the fertilizers use efficiency from 17.1 kg/kg NPK during 1970-71 to 8.1 kg/kg NPK in 1 988-89 with a possibility of a dip to 6.5 kg/kgNPK by 2000 AD has been reported (Sankaram, 1990). Although apart of this behavior may be caused due to diminishing returns of the increasing dosages of fertilizers, the reduced responses to fertilizers use may be due to declining and poor organic carbon/humus content in these soils which are important in maintenance of soil health and quality. The situation may be serious for vegetable growers •1 •
BIOFERTILIZERS IN SUSTAINABLE AGRICULTURE
where higher doses of chemical fertilizers are recommended (Singh, 1996). The decreasing fertilizer use efficiency and declining soil organic matter (SOM) content are serious concerns for low input sustainable agriculture (LISA). We are beginning to recognize the limits of chemical fertilizers particularly for soil depleted of organic matter. The indiscriminate1 application of chemicals for plants protection is becoming to cause many problems than it solves. Suicides of farmers in Andhra Pradesh and Maharashtra because of pests and diseases that could not be controlled are but the tip of the iceberg.
PLANT NUTRIENTS There are 16 essential plant nutrients which are required for normal growth, development and maturity of plants ranging from small creepers to tall trees. The macronutrients required by plants are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur; and micronutrients are iron, copper, manganese, zinc, boron, molybdenum and chlorine. Soil analyses generally indicate that most of these elements are present in soil in larger quantities than the actual nutrition needs of plants. However, many of these are bound in organic and inorganic complexes which are unavailable to plants for their uptake. Plants obtain most of their carbon and oxygen from air through photosynthesis and build up higher organic molecules. The required hydrogen is derived from water. About 95% of the plant tissues is made up of carbon, hydrogen and oxygen. The other elements are obtained by plants from soil. Of these, nitrogen, phosphorus, potassium, magnesium, calcium and sulphur are required in higher quantities than the rest of the elements. Nitrogen requirement is met from available forms of nitrogen viz. ammonium and nitrate which are added to soil through in situ biological nitrogen-fixation, and external additions of mineral fertilizers and organic manures. The micronutrients viz. boron, zinc, manganese, copper and chloride are taken up in traces by plants. Depending upon their availability in soil, they have to be applied through organic manures or chemical fertilizers. The balanced use of plant nutrients is needed for normal growth of plants. The requirements of plant nutrients can be met not only by chemical fertilizers but more advantageously by different techniques of organic recycling and largescale use of renewable sources of carrier based biofertilizers to change the system slowly from conventional to sustainable agriculture.
CONCEPT OF CONVENTIONAL, ORGANIC/BIODYNAMIC FARMING/ ECO-FRIENDLY SYSTEMS IN SUSTAINABLE AGRICULTURE The practice of ecologically sound, economically viable and culturally appropriate agriculture is generally termed as sustainable agriculture. This not only benefits the farming community in particular but the society in general. The modern technology better known as conventional technology in the west is hoavily dependent on non-renewal energy sources, viz. pesticides, and chemical fertilizers. The continuous, unbalanced and excessive use of agricultural chemicals on plant and soil is not only damaging the soil biodiversity and environment but also reduces the soil productivity potential. Moreover, the consumption of chemically contaminated food grains, fodder and animal products are jeopardizing the health of human beings and animals. •2*
INTRODUCTION
Conventional farming The technological advances made during 1950’s had caused a dramatic change/shift in mainstream agriculture, creating a system that relied more on agro-chemicals viz. herbicides, insecticides, nematicides, chemical fertilizers, new varieties of crops and labour saving energy-intensive farm machinery. This system has come to be known as conventional farming. A growing cross section of people in the world are questioning the environmental, economic and social impacts of conventional agriculture. Consequently, many individuals are seeking alternative practices that would make agriculture more sustainable (Rupela, 2005). Variants of non-conventionalfarming Nature farming: This farming was advocated in 1935 by Japanese philosopher, Mokichi Okada (1882-1955). He paved the way for its practical use through his literature and results of his experiments in field cropping. In 1953, he setup a “Nature Farming Extension Society” as an organization to promote his newly advocated farming practices. Ohito Research Farm in Japan was established in 1982 which conducts Research and Development and has become a headquarter for those practitioners. In 1992, MOA India and WSAA India branch was established in Bangalore. MOA nature Farming Model Farm was also established in whitefield, near Bangalore in the same year. The guidelines are based on the philosophy of Mokichi Okada Nature farming practice in which soil itself consists of the fire, water, and soil elements as universal life giving powers. The focus of the Nature farming is to establish, linkage between humanity and nature. MOA Nature farming is not merely considered by their followers as alternative farming system, changing from conventional method to compost and natural pesticides but embodying both the philosophy that soil has the vital energy and the harmonious relationship between man and nature. The objectives of Nature Farming includes development of agriculture, forestry and rural communities; promotion of healing dietary habits of consumers making available safe food both in quality and quantity; utilization of land effectively and other resources to increase soil productivity and conservation of energy and to reduce production cost. The basic methods to achieve the objectives are as follows: 1. To ensure production of safe and quality produce by growing crops on soils’ inherent power (Native fertility) 2. Maintenance and improvement of soil fertility by use of crop rotation, relay cropping, use of green manures, compost, natural materials rich in nutrients. 3. To control disease, insects damage and weeds though ecological methods inclusive / of utilization of companion crops and natural enemies. 4. Shall not use chemical fertilizers, plant growth regulators and feed additives. 5. Shall not apply undecomposed animal excrements and human faeces to soil. Conversion from conventional to naturefarming methods: The conversion programme should begin with a fertility building phase and prohibited inputs may not be used at any stage during changeover. The period of conversion will be decided by the guidelines Administrative Committee after going through the technical information furnished in this context.
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BIOFERTILIZERS IN SUSTAINABLE AGRICULTURE
Recommended materials for soil amendment and nutrient supply for regular and restricted use: This includes plant materials existing in Nature and Compost prepared from such materials, bring earth from another place whose safety has been confirmed; can be used for mixing with soil, crop residues and compost made of such residues, charcoals and smoked-charcoals, oil-cakes, rice bran,, fish meal, bone meal, guano phosphate, grass and wood ashes, limestone and dolomite, vermi-compost, peat Moss, biofertilizes for restricted use, kitchen waste, fermented poultry excreta and rock phosphate. Organic farming Organic farming as a philosophy has caught the imagination of farmers the world over and has been perceived as panacea for ills of conventional farming ever since Rachel Carson wrote “Silent Springs” in the last 1960s. In the developed countries, the residues of chemical imputs such as pesticides and fertilizers entering the food chain is of major concern while under Indian conditions, it is the restoration of soil productivity and conservation of the basic resource-soil that assumes significance. The basic principle of organic farming aims at the management of agro- and ecosystems. Under agro-system, the farmer has to manage the farm with coherent diversity by utilizing all the on-farm and adjacent resources. Such a practice helps to conserve the ecosystem rather than destroy it. Organic farming excludes use of agro-chemicals like chemical fertilizers and pesticides. However, organic fanning would be successful in places where sufficient organic materials are available in surroundings and on farm and proper techniques of recycling of organic matter and use of renewable resources are employed for the purpose and also under conditions of scarce availability of costly chemical fertilizers. Options on organic farming: These are as follows: Pure organic farming: Use of organic manures/compost, recycling of plant residues, biofertilizes and biopesticides without any application of chemical fertilizers and pesticides. Integratedfarming system: Recycling of local organic resources generated from dairying, fisheries, poultry, goat farming, mushroom production, agroforestry and agricultural system. This is low input organic farming. Integrated conventional and organicfarming technology: This involves integrated plant nutrient supply and integrated pest management. Biofertilizers could serve as alternate sources of nitrogen or phosphorus or both. Why organic farming may be practised?: Conventional intensive agriculture causes many problems like soil becomes poor in organic carbon and plant nutrient, increasing rates of chemical fertilizers are required every year/season to grow and get the same crop yields, control of pests and disease becomes more problematic and rivers, lakes, wells and water bodies get polluted with chemicals damaging the ecosystem. An organic farmer should have a healthy balance between nature and farming where plants and animals can grow and thrive. Organic farmers do not leave their farms to nature, they use all knowledge, techniques apd products to work with nature. Organic farming avoids the use of pesticides which dissolve easily and can quickly find their way in food chains and water-bodies. The soil is living system and must be manured to feed the soil micro-organism for their growth and biochemical activities. Nutrients are recycled by composting crop residues and
•4 •
INTRODUCTION
using farmyard manure, green manure etc. Rotation with legume crops helps in biological nitrogen fixation. International standardsfor organic farming: These were laid down by the International Federation of Organic Agriculture Movement in 1992 and are enumerated here. 1 . To produce food of high nutritional quality in sufficient quantity. 2. To interact in a constructive and life enhancing way with all natural systems and cycles. 3. To encourage and enhance biological cycles within the farming system, involving micro-organisms, soil flora and fauna, plants and animals. 4. To maintain and increase long-term fertility of soils. 5. To use as far as possible renewable resources in locally organized systems. 6. To work as far as possible within a closed system with regard to organic matter and nutrient elements. 7. To work, as far as possible with materials and substances which can be reused or recycled either on the farm or elsewhere. 8. To give all livestock living conditions which will allow them to perform the basic aspects of their innate behaviors. 9. To minimize all forms of pollution that may result from agricultural practices. 10. To maintain genetic diversity of agricultural system and its surroundings including protection of plant and wild life habitats. 11. To allow agricultural producers a living according to the United Nations human rights, to cover their basic needs and obtain an adequate return and satisfaction from their work, including a safe working environment. 12. To consider the wider social and ecological impact of the farming system.
Biodynamic farming The main objectives of biodynamic farming are as follows: 1. To produce high quality food and fibers out of potential individual farms. 2. To develop site adapted and balanced combination of plant and animal husbandry which will make farms independent of synthetic fertilizers. 3. To maintain and enhance the environment as well as the cultural life of the farm in co-operation with the social life of the region. 4. To take part in experimental research for the further development of an agriculture that is attuned to the natural world. Methods: The following steps are used in methodology. 1. Nutrients cycling and humus replacement are the foundation of a farm’s well being. It involves livestock husbandry, utilization of plant and animal residues, pasture management and crop rotation. , 2 Intensive use of biodynamic preparations in the context allows, soil, plant and animal processes on the farm to be integrated in a healthy and productive way. 3. While biodynamic method of farming stresses the importance of macro- and micro¬ nutrients and advises the use of mineral and organic forms where appropriate (eg. rock phosphate, dolomite, ground basalt, basic slag etc). It sponsors the skilful -use pf organic matter as basic factor of soil life hence fertility.
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BIOFERTILIZERS IN SUSTAINABLE AGRICULTURE
Biodynamic preparations: All the preparations can be made on the farm or obtained by biodynamic farming and gardening associations. Preparations, 500 and 501 are mixed in water and then sprayed on soil or plant and 502507 are used in composting process and in preparation of liquid manures. Biodynamic preparation (B.P.) 500 soil spray is considered to promote humus formation processes and improves soil structure and root growth. BP 501 leaf spray is reported to promote photosynthesis, yield and nutrient quality. BP 502-207 are used in compost preparations which promote cycling of plant nutrients and maintains diverse biological pathways. Biodynamic farming has been practised in Australian farms and in New Zealand on a small scale. There is need to be re-examine and confirm such preparations and methods. There is a lack of data and authentic information on methods and products. It is yet to know whether the claims are reproducible and based on scientific principles. Eco-friendly systems in sustainable agriculture Natural organic farming is not a single method but rather a variety of techniques according to a report of United States National Academy of Sciences (1989). These techniques have the common goal of reducing costs, preserving the environment, and protecting human health by lowering or eliminating use of toxic chemicals at farms. Natural farming usuallyrequires harder work and greater management skills than chemically based agricultural practices. At present times, people are conscious about the issues viz. food safety and water quality. Sustainable agriculture involves several variants of non-conventional agriculture that are often called organic, alternative, regenerative, ecology friendly or low-input. However, just because a farm is organic or alternative does not mean that it is sustainable. For a farm to be sustainable, it must produce adequate amounts of high quality food, protect its resources and be both environmentally safe and profitable. Instead of depending on synthetic and expensive sources viz. pesticides and fertilizers, a sustainable farm relies as much as possible on beneficial natural process and renewable resources drawn from the farm itself. The concept of sustainable agriculture is gaining acceptance in India because of the rapid degradation of natural resources, increase in cost of production in conventional farming and deterioration of the quality of rural life caused by environmental pollution. In India, most of the farmers are using natural products for production and protection of crops for two main reasons. The chemical fertilizers are too expensive to afford and it is risky to adopt conventional methods in over 70% of cultivated area which is presently under rainfed farming system. The most salient aspect of organic agriculture is emphasis on utilization of natural soil process viz. soil nutrients, water cycles and naturally occurring energy flow for producing nutritious foods which are free from chemical residues. The reliance is on crop rotations, crop residues, animal manures, green manures, vermi-compost, gobar-gas plant spent slurry, municipal wastes, sludge, rock phosphate enriched compost, tank silt etc. for maintenance of soil productivity and biopesticides for control of insects and diseases. A 'permaculture or natural approach where one relies on the productivity of permanent structure viz. trees, perennial species or other undisturbed plant soil system for food has been perceived to be ultimate goal of sustainable farming system. Thampan (1995) observed sporadic success in adopting organic farming by farmers of tree-based cropping system
•6*
ti
a
INTRODUCTION
involving the combination of trees, shrubs and seasonal field crop and livestock. The multiple products so obtained and enhanced on-farm employment have strengthened the socio¬ economic security of the farmers.
SOIL AS BASIC RESOURCE Soil is an important basic resource and acts as sink for disposal of different types of wastes. It is made up of solid phase 50% by volume whose components are of numeral and organic matter, liquid phase, 25% by volume is water having solution of plant nutrients. The concentration of salt in soil on dry basis may range from 100 to 1000 ppm. The content of calcium sulphate or calcium carbonate is often found more. Sulphate, nitrate, chloride, calcium, magnesium, potassium and sodium bicarbonate are also found in liquid 'phase. Besides, these elements other nutrients are found in traces. The gaseous phase has oxygen (20%), nitrogen (78.6%) Argon (0.9%) and carbofi dioxide (0.50%) against atmospheric air which has 20.0% oxygen, 78.03% nitrogen, 0.94% Argon and 0.03% carbon dioxide. The proportion of carbon dioxide in soil air is about 16-fold higher than atmospheric carbon dioxide. This is due to soil respiration and heterotrophic activity in soil conditions I ; Healthy soil Soil is essential to agriculture and is a complex living system besides the inek component. The loose but coherent structure of good soil holds moisture and invites aifflow. Ants and earthworms mix the soil in natural way. Bacteria viz. Rhizdbium living in the root nodules of legumes viz. pulses, soybeans and groundnuts, fix atmospheric nitrogen in association with the host. Other soil micro-organisms including fungi, actinomycetes and bacteria decompose organic matter, thereby, mineralizing more nutrients and actively participating in different plant nutrient cycles (Gaur et al., 1971). Microorganisms also produce polysaccharides and mucilaginous substances that bind the primary and secondary soil particles into aggregates (Gaur and Subba Rao, 1976; Gaur et al. 1972). To improve the soil quality, soil must be fed with crop residues, green manures, oilcakes, farmyard manure etc. The use of efficient and competitive strains of biofertilizers may be of special significance to improve the nutritional quality of soil. Soil is a favourable medium for the growth and development of soil microorganism. Bacteria are found in Indian soils in the range of 1 0—30 millions, followed by actinomycetes (xlO5), fungi (x 104), algae (xlO3), Azotobacter (xlO2). Most of them are principal decomposers of organic matter 'in soil and help in formation of humus substances. Few bacteria are involved in fixation of atmospheric nitrogen and some of the microbes are instrumental in phosphate solubilization. They participate in different biological cycles viz. carbon, nitrogen, phosphorus, sulphur and transformations of iron, manganese, potassium, zinc, arsenic, selenium etc. Sustainable agriculture does not represent a return to old methods but it combines traditional conservation-minded techniques with modern technologies. Emphasis is placed in crop rotation, building of soil fertility, use of soil microorganisms as biofertilizers to improve soil health, diversifying crops and livestock and controlling pests naturally. Whenever possible external sources viz. commercially procured chemicals and fuels are replaced by resources found on or near the farm. These internal sources include, solar, wind
•7*
BIOFERTILIZERS IN SUSTAINABLE AGRICULTURE
or biogas as energy, bacterial or fungal biofertilizers, fixing atmospheric nitrogen, phosphate solubilization or accelerating the nutrient mineralization process. In some cases, external resources may be essential for reaching sustainability. As a result, such farming systems can differ considerably from one and another because each tailors its practices to meet specific production, environmental and economic needs.
RENEWABLE RESOURCES OF ENERGY AND PLANT NUTRIENTS Regular additions of crop residues, compost and other organic materials viz. animal and green manures to soil is another central feature of sustainable agriculture besides crop rotation etc. The benefits from these operations are obvious and discussed in the proceedings. Organic materials also feed soil microorganisms and earthworms and result in build up of microbial biomass (Bhardwaj and Gaur, 1985). Leguminous green manuring plants fix substantial quantities of nitrogen and supplement or completely replace chemical fertilizers in crop production. Green manures help to control weeds, insect pest and soil erosion. By raising a diverse assortment of crops and livestocks, a farm can buffer itself against economic, seasonal and biological risks. Diversity results from mixing species and varieties of crops and systematically integrating crops, trees, livestocks in the farming system.
MICROBIAL BIODIVERSITY IN SUSTAINABLE AGRICULTURE The biosphere or part of the earth bnd its atmosphere where life is found is made of different size of ecosystem regulated by solar energy. Ecosystems have both biotic and abiotic components. The biotic component comprises closely interacting groups of flora and fauna having varying energy needs which comprise of heterotrophic, chemotrophic and photoautotrophic microorganisms. Biodiversity refers to the richness of life as manifested by their morphological, cultural and biochemical characteristics of microorganisms and their interdependence in a habitat. It is because of biodiversity that each ecosystem functions as the basic life support system of the planet earth. Biodiversity sustains the food and nutrition security of human beings and mediates the ecological process by resisting environmental perturbations in a given soil and climatic conditions. Presently greater emphasis is, being given on the biodiversity of above-ground biotic components belonging to plant and animal kingdom. The living organisms in soil and their diversity in relation to their contribution to sustainable agriculture often do not receive adequate attention. Without taking into consideration the magnitude and biodiversity of soil biota which is more or less equal to above ground mass, the understanding of the global diversity will be fragmentary. Biodiversity in soil Soil is a natural habitat of an array of diverse groups of organisms related to the plant and animal kingdoms. They vary in morphology and are found from microscopic to large bodies belonging to flora and fauna. There are organism which are beneficial to improve soil properties and plant growth but some pathogenic types damage the agricultural crop by causing plant diseases viz. root- and stem-rot.
•8*
INTRODUCTION
The decomposition of plant and animal residues in soil, mineralization (conversion of ctganic nutrients to inorganic form) of plant nutrients, solubilization of insoluble forms of nutrients, biological nitrogen-fixation, mediation in natural cycles etc. are processes in which soil biota activity participate. In the absence of soil organisms, the biological process will stop, making life of plants and animals impossible on the earth. The soil organisms comprise of fauna and flora. Soilfauna: Their biomass is smaller as compared to soil flora. Soil fauna or soil animals comprises large varieties of organisms with different shapes and sizes and adaptive strategies. Based on their sizes and adaptive strategies, they are divided into microfauna, mesofauna and macrofauna. I Microfauna: Organisms belonging to this group are very small with an average size of less than 0.2 mm. They are found in soil pores and water films that cover soil particles and feed on microflora and other microfauna. Many hre parasitic on higher plants and some persists on plant residues. Nematodes and protozoans are the main representatives of this
f
group. | Protozoans are one-celled organisms confined mostly to surface horizon of soil. They are slightly bigger than bacteria and usually the most varied groups viz. flagellates, amoebae and ciliates. Aeration and availability of food materials are the facts influencing their population. Their population in normal soils varies between 104and 105/g of dry soil. Protozoans are important predators of bacteria resulting in partial sterilization of soil exerting a regulatory control on the bacterial population of soil. They may prove beneficial in control of pathogenic bacteria in the root zone. Nematodes are found in all types of soils and are among the most abundant soil fauna. Their numbers are highest ranging from 104to 106/m2in cultivated soils. Nematodes are composed of those that are predatory on bacteria, fungi and protozoa, parasite on higher plants and those that feed on decaying organic matter. Nematodes often cause serious damage to plants and over 500 species of plant parasitic nematodes are known to exists in soils. These round and spindle-shaped organism have adaptable mouthparts and pointed form. As such, it is easy for them to penetrate plant tissues. Though a major crop pests, nematodes also possess the potential to suppress the population of fungi and bacteria in the root zone i Mesofauna: Organisms of this group range in length from 0.2 to 2 mm. Population densities in favourable soil conditions, can rise upto 106/m2 of soil surface. Mites and Collembola are of common occurrence in soil. These organisms degrade plant litter and are predators of other mesofauna and fungi. Although present in all soil layers, maximum population is recorded in the rhizophere of plants. Macrofauna-. This group comprises of small mammals, insects, mites, centipedes, millipedes, slugs, snails, spiders, earthworms etc. They exceed 10 mm in size and include predators and feeders of plant materials. They contribute to soil fertility by mixing organics in soil and improve physical condition of soils. On death, their substantial residues are degraded in soil and release plant nutrients. The most important members of this group from point of view of soil fertility are termites, ants and earthworms. I Termites and ants are common in tropical, subtropical and mediterranean soils. Through Iheir activities, they modify the organic substance of soil either by digestion or translocation. Termites utilize undecomposed organic matter as food resource and thus play a role in their
•9 •
BIOFERTILIZERS IN SUSTAINABLE AGRICULTURE
degradation in soil. Their biomass in soil is much less than earthworms. Termites may damage the growing plants when present in large numbers in soil, depleted of all organic matter on the surface soil making it vulnerable to erosion. Earthworms are well known representative of soil macrofauna having the maximum influence on the physical and biological properties of the soil. They are found in large numbers in soil which are moist and rich in organic matter, exchangeable calcium and phosphates. In rich cultivated soils, their population may range between 0.6 and 2.5 million/ ha with live weight ranging between 300 and 1250 kg/ha. In unfavourable soils, their population may drop to even less than 30,000/ha with a biomass of about 15 kg/ha. Earthworms are classified into detrivores and geophages. The detrivores include epigeic and anecic forms, and geophages comprise the endogenic earthworms. The epigeic bring the fragmentation of organic materials restricted on the soil surface. This activity has no effect on soil structure. The anecics feed on litter mixed with soil particles and produce surface casts. The endogenic earthworms live within the soil deriving nutrition from organically rich soil they ingest. The common examples of detrivores which are involved in humus formation and vermicomposti ng are Perionyx excavatus, Eiseniafoetida, Eudrilus euginae, Lempitomauriti, Octachaetona serrate and Octachetona surensis. The common example of humus feeders (Geophages) is Octachaentona thustoni. Earthworms ingest organic debris alongwith sufficient soil particles. The ingested materials is subjected to enzymatic and grinding action before excretion as ‘casts’. In rich soils, the casts may work out to more than 15 tonnes/ha. The organisms may pass through bodies annually around 40 tonnes soil and organic matter/ha. It is claimed that earthworms cast are richer in organic matter, available plant nutrients, and microbial population. The accelerated microbial population and their activities are helpful in improving the physical, chemical and biological properties of-the soil. However, data substantiating these claims are fragmentary, hence, systematic investigation are required to confirm the claims of the promoters of vermicomposting. Soilflora: It is represented by diverse type of microorganism viz. bacteria, actinomycetes, fungi and algae. The living roots of higher plants are also important component of soil. The biomass of soil flora is higher than the biomass of soil fauna. This group performs important functions viz. soil granulation, organic matter mineralization, fixation of atmosphere nitrogen, production of plant growth promoting substances etc.(Dahiya and Srivastava, 2005). The organic transformations initiated by soi 1 fauna are carried forward by microflora and cumulative effect of interaction viz. synthesis of microbial polysaccharides, bindingeffectoffungalmycelia and plant roots bring about significant improvements in soil structure and physical condition of soils. Soil enzymes, vitamins, amino acids and harmones etc. are produced in soil due to microbial processes. Bacteria: Soil bacteria is the most abundant group of all microflora present in soil. Indian soils in normal conditions have 10 to 25 millions/g bacteria in dry soil. These are simplest and smallest forms of life, present in the soil. Their growth rate is faster than other microflora of soils. Most of the soil bacteria are heterotrophic and depend on their needs of carbon and energy on native and added fresh organic mattbr. Heterotrophic bacteria alongwith other microorganism extensively participate in organic matter decomposition, release of plant nutrients and humus formation. The chemoautotrophs are of special significance because they participate in nitrification process and nutrient cycling viz. sulphur, iron etc. Soil bacteria in general are involved in cycling of plant nutrients.
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