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There is increasing awareness all over the world regarding the need for establishing of organic and sustainable system of agriculture. The humus and organic fraction of tropical and subtropical soils are under constant threat and depletion due to environmental and inadequate replenishment. The maintenance of a good soil fertility and the regular use of organic manures and bioiertilizers are of great importance to keep up the farm in good state of productivity involving natural processes in its place. This book highlights various sources of organic and biological agents which can be used for organic farming and as well as for maintenance of soil fertility over years'. Organic manures are byproducts of processes of decomposition of organic materials available both in rural and urban areas. Organic manures have been used by the farmers from the beginning of agriculture. But it was neglected in India during the past two to three decades. The production of bioiertilizers is a new development and they are produced by isolation, selection and culturing on mass scale of specific microorganisms such as bacteria or fungi. Nitrogen fixing and phosphate solubilizing microorganisms are produced as biofertilizers arid made available to farmers to supplement nitrogen and phosphorus needs of the crops with either organic or chemical fertilizers. Moreover, these inputs are inexpensive and eco-friendly.

I. Introduction India has been deeply concerned about the food security on the one hand and health and welfare of its people on the other. Agriculture has been traditionally the backbone of Indian economic progress and development. The role of agriculture including animal husbandry, dairying and fisheries accounts for some 33 per cent of the country’s gross domestic product (GDP) and about 65 per cent of the work force depends directly or indirectly on agriculture for its livelihood and support. Along with the food grain, the production of vegetables and fruits has also been increased to meet the nutritional security of the people. India is the second most populated nation with a geographical land area of about 329 million hectares (Table 1). The gross cropped area is 185.5 million hectares with a net sown area of about 142.5 million hectares. Currently area under assured irrigation is estimated to be 50.10 million hectares which is 35.15 percent of the cultivated area which has progressively risen to this level due to the expansion of major and medium irrigation projects including harnessing of ground water reserves excluding tanks (Shantaram, 1998). A substantial part of the net cultivated area which works out to be about 92.3 million hectares is rainfed depending on the vagaries of rains. The forest area (68.07 million hectares) only 22.3 per cent which is much less than the desired level because the national forest policy demands it at least 66 per cent in hills and 33 per cent in plains. However, it is not feasible to divert land for forest plantation due to obvious population pressure on agricultural land. However, the advantages of forest can be harnessed by growing trees on marginal lands alongwith crops through agroforestory practices for restoring ecological balance.

Type and Potential of Organic Residues A number of diverse sources of organic materials are available for recycling in agriculture. These are mostly of plant origin and recycled either directly or after having being used as feed or food by animals and humans. In view of high organic content and mineral nutrients in the biomass, these are considered as valuable inputs to improve the soil fertility and crops production. Organic resources are low cost inputs but are valuable based on its potential for nutrients and organic matter content. Attractive Features of Organic Resources • Organic matter is the basic resource of several essential plant nutrients. • It buffers the effects of pH dependent changes on nutrient availability. • They are generated close to their use. • They are renewable as they are generated regularly. • With increasing demand for increasing food production, the potential of organic resources is expected to rise. • Farmers are familiar with organic resources from time immemorial.

I. Crop Wastes Crop residues are the main sources for recycling of the organic and plant nutrients removed from the soil during the growth of crops. These residues have competitive uses such as fuel and cattle feed. There was an estimated demand of 583.6 million tonnes of dry fodder against the supply of aljout 398.8 million tonnes (Singh, 1997). Besides the use of crop residues as animal feed, industrial uses of crop residues also pose competitive demands. The potential of crop residues of some principal crops was worked out by Bhardwaj (1995). It was assumed that not more than one third of the total crop residues (273.63 million tonnes) was available for recycling as plant nutrients (Table 21). Out of a total 5.61 million tonnes (N+P2 O5 +K2 O) available in the form crop residues, only 2.47 million tonnes can be mobilized either through composting or in situ incorporation or mulching. Based on these estimations, Sekhon (1997) projected that approximately 4.82 and 5.79 million tonnes of N+P2 O5 +K2 O will be available from recycling of crop residues by the year 2011 and 2025 with utilizable value of 2.21 and 2.26 million tonnes respectively (Table 22).

1. Oil Cakes Several varieties of oil seeds are produced in India. Oil seeds contain 40 to 50 percent oil and residues left after extraction are known as oil cakes. Oil seed cakes are generally referred as concentrated organic manure because of their high content of plant nutrient, nitrogen in particular as compared to conventional farmyard manure or compost. Oil cakes also invariably contain 2 to 15 percent oil depending on the method of extraction. Oil seeds are further demarcated into edible and non-edible oil seed cakes depending on their palatability to animals. Both type of oil seed cakes can be used as organic manures, but edible oil seed cakes are generally used as animal feed as warranted by socio-economic reasons (Bhardwaj, 1995). Non-edible cakes are generally used as organic manure to supply major plant nutrients like nitrogen, phosphorus and potassium. Potential of Non-edible Cakes The authentic estimates of quantity of non-edible cakes produced in the country are not available because the oil yielding trees are grown and scattered our vast tract of the country. Only a part of oil bearing seeds of these trees are being collected and processed. According to an estimate, annual production of non-edible oil seed cakes was of the order of 3.8 million tonnes annually which on average can provide 87, 25 and 57 thousand tonnes of N, P2 O5 and K2 O respectively (Singh and Gurumurti 1984).

India produces around 33 mt. of fruits and 50 mt. of vegetables annually (Chadha and Bhargava, 1997). It is estimated that 10 to 15 percent of total produce is available as organic waste for recycling in agriculture (Nand et al., 1996). In addition to processing of fruits and vegetables results in production of around 5 mt. of solid wastes (Table 66). Most of these wastes contain organic and plant nutrients (Table 66). There are still large amounts of wastes that are not being completely utilized. In most cases, these wastes are pro-duced from isolated sources and not by large centralized.companies. In practically all cases, horticultural and vegetable products are processed in relatively small canning plants and distributed for use generally in the same geographical area where the produce is grown, this is true world over since fruit and veg-etable wastes cannot be usually transported long distances in view of their bulk, high moisture and low to moderate feeding value relative to conventional feed.

Solid wastes, which are left after the fermentation process is complete, may be potential sources for use as fertilizers and feed stuffs. I. Antibiotic Fermentation Wastes Antibiotics are produced by microoganisms and have capacity, in dilute solution, to inhibit the growth or even destroy the other microorganisms. They are produced on a large scale using fermentation process except chloroamphenicol which has been produced synthetically since 1948. Solid wastes remaining after the liquid containing the antibiotic has been extracted from the fermentation broth need to utilised. This is usually done by filtration. The solids are a heterogeneous mixture of hyphae of the producing organism, unused media, defoaming oils and metabolic products of the micro-organisms, the most important of which is residual antibiotic. The levels of residual antibiotic can vary a great deal.

There are about 3000 tanneries processing 6000 tonnes of hides and skin annually in India. Large amounts of solid and liquids are generated in tanneries containing N and heavy metals. The treatment of tannery waste waters generates sludge which contain a large variety of organic and mineral components. The amount of sludge from a single tannery may be obtained up to 10,000 tonnes/ Yr. Fresh Sludges undergo preliminary fermentation on liquid separating plots which are stored in piles where further decomposition takes place. As a result of decomposition process, partially biodegraded material resembling compost is obtained. It looks like deep black earthy material. The chemical composition indicates the possibility of using it in agriculture. The hides of infected animals many contain anthrax germs and be contaminated with heavy metals particularly chromium in the sludge which depends on the technology for hide tanning and the methods used in a sewage treatment plants. The sludge from tanneries using chromium in the treatment process are not suitable to be used as fertilizer as they contain high amount of chromium. Co-composting of these wastes with crop residues could provide good quality compost and the heavy metal content would get diluted and reduced per unit weight.

I. Rock Phosphate Rock phosphate is natural source of phosphorus. It occurs as natural deposits of rock in Morocco, U.S.A., Egypt, Poland, Russia, Tunisia, Algeria, Brazil, Nauru and some Islands in the Pacific and the Indian ocean. It contains 20 to 35 percent phosphoric acid (P2 O5 ) but this phosphorus is in insoluble form. In India, some of rock phosphates occur in Udaipur and Jaisalmer districts (Rajasthan), Purulia (West Bengal), Singhbhum (Zharkhand) and Mussorie (Uttrakhand). Most of these phosphates are classified as low grade phosphate since its phosphoric acid content is less than 20-25%. The total reserve of low grade rock phosphate is estimated to be around 165 million tonnes of which nearly 70 million are reported to occur in Rajasthan. The other economically viable deposits are in Mussorie (Uttarakhand), Jhabua district (Madhya Pradesh), Singhbhum (Zharkhand) Kasipatnam (Andhra Pradesh) and Purulia district (West Bengal). Rock phosphate is the basic raw material for manufacture of superphosphate and other kind of phosphatic fertilizers. It is reported above that India has mostly low grade rock phosphate. Hence India has to spent huge amounts of foreign exchange to import high grade rock phosphate containing around 32-35%, P2 O5 for manufacture of phosphatic fertilizers.

The terms such as organic, natural, biological, biodynamic, altemative and sustainable farming have entered the agriculture vocabulary. Inspite of these differences in terminology, basically identical ideologies, ideas and technologies are reflected. The common objectives of all the system are to develop farming methods to restore, maintain or build-up soil productivity, to protect the environment instead of causing pollution, produce safe and healthy food, and preserve or help the small farmer. In Japan, the farmers study the nature, learn from it and apply the knowledge on their farms. For instances growing plots should also be mulched with straw or plant residues, this imitates the conditions in natural forest where ground is never bare. Instead of using pesticides, strong herbs or plants can be grown around vegetable plots to ward off the insects. To keep the soil health natural, organic fertilizers are used. Soil microorganisms and earthworms take care of the processes involved in decomposition and mineralization of the organic substances, fix atmospheric nitrogen, solubilise insoluble forms of phosphate and produce natural growth promoting substances and antibiotics, The concept of sustainable agriculture is gaining acceptance and momentum because of rapid degradation of natural resources, increase in the cost of production in conventional agriculture system and deterioration in the quality of rural life caused by environmental pollution. Moreover it is risky and uneconomical to practise conventional agriculture in over 70 percent of the cultivated area in India which is presently under rainfed farming. Much of the know how to practice organic farming models has rested on the individual farmers till now. They however do not have the benefit of appropriate technology and scientific information and also institutional support to ensure success of the new farming system.

Proper soil management without impairing soil health is the prerequisite for achieving higher productivity from agriculture land. The arable soils of tropics and subtopics are poor in organic matter due to high temperature and intense microbial activity. The importance of organic matter in improving soil fertility through maintenance of optimum levels of soil organic matter as well as plants nutrients is well recognized. There is need to encourage more ecofriendly and productive farming system. A growing number of farmers, ecologists and scientists are coming to conclusion that conventional farming can not be sustained because in the end it does more harm than good and it is high time to think of sounder ways of farming which are healthy for the soil, environment, plants, animals and human beings. The practices of economically sound, viable and culturally appropriate agriculture is termed as sustainable agriculture. The excessive and imbalanced use of chemical fertilizers and pesticides on soil and plant in not only harmful to soil microflora and fauna but also reduces the productivity potential of the land. The conventional intensive agriculture has depleted the soil organic matter content and plant nutrients besides the susceptibility of crops to pest and disease. Nitrates the ultimate product of N- fertilizers pollute the ground of water and food, has higher levels of non-protein nitrogen (NPN). Increasing levels of NPN in human bodies have been reported. Soil is a dynamic living system and if it is not manured to feed soil biota, soil health gets deteriorated which is essential for cycling of plants nutrients.

The biosphere or part of the earth and 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 heterotrophic, chemoautotrophic and photoautotrophic microorganisms. Biodiversity refers to the richness of life as manifested by their morphological, cultural and biochemical characteristics of microorganism and their interdependence in 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 placed 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 considerations the magnitude and understanding of the global diversity will be fragmentary. However, management of below ground biodiversity is being focused presently by several national and international bodies.

Nitrogen is the most important plant nutrient for increasing crop productivity. A few prokaryotic microorganisms are able to fix N2 directly mediated by enzyme nitrogenase. Annual biological nitrogen fixation (Table 96) is estimated to be around 175 million metric tonnes per year of which about 139 million tonnes (79%) are accounted for by terrestrial fixation (Burns and Hardy 1975). The nitrogen fixers involved are metabolically diverse but the process is similar and depends upon (1) nitrogenase (Nase) enzyme complex (ii) a high energy requirement (ATP) (iii) anaerobic conditions for nitrogenase activity (iv) source of strong reductant. The symbiotic process is known to be one of the important contributors to the nitrogen cycle both from agricultural and ecological points of view. The soil bacteria of the genus Rhizobium colonizes and forms nodules on the root of leguminous plants such as clover, lucerne (alfalfa), pea, chickpea, pigeonpea, beans, groundnut, Vigna species etc. The nitrogen uptake in legumes by some unknown process was demonstrated through agronomic experiments by J.B. Boussigault in 1838 which was opposed by Liebig and others. However, Hellriegel and Wilfarth’s experiments (1886-88) clearly showed that the growth of non-leguminous plants, barley, oats etc. was directly proportional to the amount of nitrate supplied while in case of leguminous no such relationship existed and growth of the leguminous plants picked up in some cases after the seedling stage. Beijerinck (1888) isolated the bacterium from the root nodules in pure culture which lead to study their morphological characteristics and physiology.

Frankia is potent nitrogenous biofertilizer for forest trees since it establishes symbiotic association with non-leguminous plants. Nitrogen fixing non leguminous trees thrive in temperate condition. The species belong to Casuarinaceae are an exception and grow successfully in tropical areas. Alnus for temperate regions and the genus Casuarina for tropical and sub-tropical regions stand out examples of the benefits they provide to ecosystem by the way of nitrogen fixation. They have an excellent potential to adapt themselves to grow under diverse geographical and environmental conditions providing enough fuel, fodder, pulp and timber. The microsymbiont within these root nodules of non-leguminous plants has been identified and designated as Frankia (Becking, 1970). Historical Developments First of all Boussingault, a French farmer during 1838 drew attention that non-legumes were capable of fixing atmospheric nitrogen. The roots of Alnus were described as warty brownish biomass as large as man’s fist (Woronin, 1866). Frank and coworkers (1887a, b, 1891) studied the nodulated nitrogen f ixing trees regardless of whether they were leguminous or non-leguminous (actinorhizal). Frank believed that the bacteroids were protein deposits but subsequently he named the causative organism as Frankia subtilis. Moller (1885, 1890) reported the causative organism in the nodules as plasmodia and Frank also revised his opinion and pointed out that the causative organism was a fungus. Such conflicting results were due to imperfect techniques to differentiate between vesicles and sporangia. Later the organism was renamed as Frankia bruchorstii to honour Frank and his coworker, Brunchorst (Moller, 1890).

Azolla, a fresh water fem is a rich source of nitrogen especially for low land rice farming. It is found in rice paddies in many tropical countries like China, India, Korea, Philippines and Vietnam. The agronomic importance of Azolla lies in its ability to fix atmospheric nitrogen through the symbiotic association with a blue-green alga, Anabaena azolae. The symbiotic association can fix nitrogen proportional to its biomass produced. When Azolla is grown in paddy f ields and subsequently incorporated as green manure, the nitrogen contained within Azolla biomass is mineralized during the process of decomposition. Azolla is a genus of small aquatic fern comprising 7 living and 25 fossil species, which is globally distributed. It occurs on still water ponds, lakes, swamps, lagoons and paddy fields in both tropical and temperate regions. Because of its rapid growth, high nitrogen percent and its ability to grow in stagnated waters, it has been used as organic manure in Vietnam and China for centuries. Its use in India and other countries is relatively recent. Azollla pinnata is native to India and widely distributed.

There are several bacteria which fix atmospheric nitrogen and do not have a symbiotic partner such as a plant. There are conclusive evidences regarding nitrogen gains due to free living bacteria (Dart and Day, 1975) The diazotrophic bacteria have been classified based on the mode of nutrition and oxygen requirement (Alexander, 1977, Knowles, 1977). Free living nitrogen fixing bacteria fix nitrogen in soil and their population in rhizosphere of plants are significantly higher than in non-rhizosphere soils Although the economic and ecological significance of many of these bacteria have yet to be established, the most promising diazotrophs are Azotobacter, Azospirillum, Beijerinckia and Clostridium. Azotobacter and Beijerinckia are some of the most preponderant, non-symbiotic nitrogen fixing bacteria. Studies on these organisms in Indian soils have been done earlier by Rangaswamy and Sadasivam (1964) Sen and Barooah (1964) and Jagtap and Bhide (1971). Among the free living bacteria, Azotobacter is the most intensively investigated. Several species viz., A. chroococcum, A. vinelandii, A. macrocytogenes, A. agilis and A. insignis were reported but A. chroococcum is the most common specie encountered in arable soils.

The accumulation of nitrogen under non-leguminous and cereal cropping systems seem to be generally universal at least in the tropics. Free-living heterotrophic nitrogen fixing bacteria are very widely distributed taxonomically, geographically and ecologically. But only a few genera and species are known to possess the potential for high amount of nitrogen fixation. Azospirillum has shown high nitrogen fixation attributes. The association of Spirillum lipoperum (Azospirillum brasilense) and Digitaria decumbens was reported by Dobereiner and Day (1974). I. Spirillum The description of members of genus Spirillum was available as early as 1670s by Leeuwenhoek (Dobell 1960 and Muller 1773). But the genus Spirillurn was created in 1832 by distinguishing it from phototrophic spirilla which were placed in a separate genus Thiospirillum (Ehrenberg, 1838). The subsequent developments of the taxonomy of the chemo- heterotrophic spirilla which generated knowledge of their characteristics, were extensively reviewed by Giesberger (1936) and Williams (1959 a, b).

Rice is grown in about 40 million hectares of land in India and nitrogen requirement for the crop is 60 lakh tonnes based on the present levels of consumption. Rice production has to be sustained and increased to provide staple diet to our increasing population. Blue green algae is a potentional biofertilizer in rice because of their capacity to meet both carbon and nitrogen requirement naturally from the air. They are microscopic algae which are collectively called phytoplankton produce basic organic matter forming the first link in food chain and alongwith replenish the oxygen content of atmosphere. Algae contain proteins, Vitamins, iodine, bromine and substances of antibiotic and stimulatory nature. The soil algae are divided into chlorophyta (green algae) cynophyta (blue green) bacillariophyta (diatoms) and xanthophyta (yellow-greens). De (1939) suggested that fertility of rice fields is maintained due to the growth of blue-green algae. Different types of blue-green algae have been reported to colonize the rice fields. The cells such as heterocysts in Anabaena, Nostoc, Tolypothrix etc. which have capacity to fix atmospheric nitrogen under aerobic condition and unicellular and non- hetercoystous forms also fix atmospheric nitrogen under microaerophilic conditions.

Phosphorus is one of the essential plant nutrients, which is required in optimum amounts for proper growth of plants and soil biota. Being a constituent of ATP it is involved in various processes such as cell division, energy generation and transfer of genetic characteristics and regulation of metabolic pathways (Theodorou and Plaxton, 1993). Phosphorus constitutes about 0.2% plant dry weight (Schachtman et al., 1998). The average soil contains 0.05% phosphorus but only one tenth of this is available to plants due to its poor solubility and chemical fixation in soil (Narayansamy et al., 1981, Barber, 1984). About 98 percent of Indian soils have inadequate supply of available phosphorus (Ghosh and Hasan 1979, Hasan, 1994). A survey of Indian soils showed that out of 363 districts, only 2,2% were high, 51.5% medium and 46.3% were low in phosphorus content (Ghosh 1982). The problem of P fertilization may become serious in coming years because of the fact that manufacture of phosphatic fertilizers requires the use of non renewable resources such as high grade rock phosphate and sulphur which are becoming costlier. The situation is further aggravated by the fact that P is readily fixed in the soil and the average utilization efficiency of added fertilizer P by plants ranges from 15-25% only (Gaur 1982, 1990). The recent report showed that 42 per cent of soil samples fell in low category, 38 per cent in medium and 20 per cent in high category (Motsara, 2002). It has been observed that the vast alluvial tracts of the country are either low or medium in available P. Hence they need P application at recommended rates.

The term ‘mycorrhizae’ was coined more than a century ago (Frank 1885) describing that the roots of most plants are colonized by fungi and transformed into fungus roots organ. Mycorrhizae result from a mutualistic symbiosis between plant roots and certain fungi. Roots of most flowering plants live in mutual symbiosis with mycorrhizae which bio-tropically colonise the root cortex and extra-metricial mycelia help the plant to obtain plant nutrients from soil (Barea, 1991). These fungi are ubiquitous in soil and are found in the roots of many Angiosperms, Gymnosperms, Pteridophytes and Thallophytes (Mosse et al., 1981). The mycorrhizal fungi perform the function of root hairs. The fungus takes carbohydrates from the plant and in turn supplies the plants with nutrients, hormones and protects it from root pathogens. The dependency of fungal species on host plant ranges from obligate to facultative (Brundrett, 2002; Read and Perez-Moreno, 2003). The mycorrhizal plants have greater tolerance to toxic heavy metal, nigh soil temperature, soil salinity, unfavourable soil pH and to transplantation shocks. They play an important role in increasing plant growth and nutrients uptake (Bagyaraj, 1992, VasanthaKrishna and Bagyaraj 1993). These fungi can be used to promote biotechnologically developed plant in soil (Varma and Schuepp 1994).

Introduction Conventional agriculture is highly dependent on fossil fuel based mineral fertilizers to compensate for removal of plant nutrients by crops. Chemical fertilizers are not only in short supply but also are very costly. The preparation and use of organic manures are not being practiced in a scientific manner to harness the plant nutrients removed by plants, animals and humans. The application of chemical fertilizers to soil alone and in an imbalanced way has resulted in deterioration of soil health and its quality. The use of chemical fertilizers has to be reduced to check the soil and water pollution and simultaneously the role of soil microorganisms has to be augmented by different ways such as greater use of biofertilizers. Moreover, the demand for organic food particularly both in developed and developing countries is on rise which opens up immense possibility to use organic manure and biofertilizers for production of foods grains, fruits, vegetables, spices, tea and coffee. Therefore, the production and the use of biofertilizers assumes greater significance and could be an excellent biological alternative to chemical fertilizers.