1. GENERAL INTRODUCTION

Transcription

1 1 1. GENERAL INTRODUCTION India, the second largest populous country, mostly depends on agriculture for living. Agriculture primarily depends on soil, which is a living body, because it consists of microflora such as bacteria, actinomycetes, fungi and algae. In tropical and subtropical agricultural land, normally there are more than ten crores of microorganisms in one gram of soil. Among the ten crores of microorganisms, only 5 7% is harmful, while the rest are beneficial in nature and extremely useful in agriculture (Chowdhury and Mukherjee, 2006). In modern agriculture, use of chemical fertilizers is essential for sustainable yield but these are not ecofriendly. The chemical fertilizers pose a health hazard and microbial population problem in soil besides being quite expensive and making the cost of production high (Chandrasekar et al., 2005). Indiscriminate use of chemical fertilizers has developed disturbances in the soil reaction, development of nutrient imbalances in plants, increased susceptibility to pests and diseases, reduction in legume root nodulation and plant mycorrhizal associations, decrease in soil life and environmental hazards such as water pollution and soil humus reduction. One of the major effects of such activities is gradual decrease in the number of useful microorganisms in agricultural soil. The problem is so intensive that, in many agricultural land of our country less than one crore of microorganism has been found in one gram of soil (Chowdhury and Mukherjee, 2006). Because of this reasons, not only the soil is polluted through

2 2 environment destabilization but the yield of agricultural produce also fluctuating alarmingly. In such a situation the biofertilizers play a major role. In recent years, biofertilizers have emerged as a promising component of integrating nutrient supply system in agriculture. Our whole system of agriculture depends in many important ways, on microbial activities and there appears to be a tremendous potential for making use of microorganism in increasing crop production. Microbial fertilizers are an important part of environment friendly sustainable agricultural practices (Bloemberg et al., 2000). Biofertilizers include mainly the nitrogen fixing, phosphate solublizing and plant growth-promoting microorganisms (Goel et al., 1999). 1.1 CONCEPT OF BIOFERTILIZERS The term Biofertilizer or more appropriately Microbial inoculants can generally be defined as preparation containing live or latent cells of efficient strains of nitrogen fixing, phosphate solublizing or cellulolytic microorganism used for application to seeds, soils or composting areas with the objective of increasing the number of such microorganisms and accelerate those microbial process which augment the availability of nutrients that can be easily assimilated by plants (Borasate et al., 2009). 1.2 HISTORICAL DEVELOPMENT OF BIOFERTILIZERS Inoculation of plants with beneficial bacteria can be traced back to centuries. Although bacteria were not proven to exist until Von Leeuwenhoek in 1683 discovered microscopic animals, their utilization to stimulate plant growth

3 3 in agriculture has been exploited since ancient times. Theophorastus ( BC) suggested the mixing of different soils as a means of remedying defects and adding heart to the soil (Vessey, 2003). From experience farmers knew that when they mixed soil, taken from previous legume crop with soil in which non-legumes were to be grown, yields often improved. By the end of the 19 th century, the practice of mixing naturally inoculated soil with seeds became a recommended method of legume inoculation in the U.S.A. A decade later, the first patent ( Nitragin ) was registered for plant inoculation with Rhizobium sp. (Nobbe and Hiltner, 1986). Eventually the practice of legume inoculation with non-symbiotic, associative rhizosphere bacteria, like Azotobacter, was used on a large scale in Russia in 1930s and 1940s. Bacillus megaterium for phosphate solublization was used in the 1930s on large scale in Eastern Europe. In India, from 1920 onwards Joshi Desai, Vyas, Biswas and Acharya worked on phosphate requirements of legumes for better recuperation of soil nitrogen and on anaerobic digestion of organic matter at Imperial Agricultural Research Institute. At the same time, Madhok introduced the practice of using bacterial cultures for beerseem (Trifolium alexandrium) in Punjab. Sanyasi Raju and Rajagopalan worked on root nodulation of Bengal gram and groundnut at the Madras Agricultural College, Coimbatore (Subbarao, 1977). The production of rhizobial inoculants was first undertaken at IARI, New Delhi in 1956 although its commercialization started in late 1960s when soybean was introduced for the first time in the country. Inoculants for pulses, oilseeds and fodder legumes were also produced. The processes of development of rhizobial inoculants for various

4 4 legumes in India has made considerable progress following the field evaluation of the inoculants on yields of various pulses, soybean, groundnut and fodder legumes was carried under the All India Coordinated Research Programmes of the respective crops by the Indian Council of Agricultural Research, New Delhi. The use of inoculants has considerably increased over the years and a number of private producers have come into operation. It is therefore, imperative to control the quality of inoculants. Accordingly, the Bureau of Indian Standards has sprung into action and specific standards for Rhizobium, Azotobacter, Azospirillum and phosphate solublizing bacterial inoculants have been brought out. Some of the nitrogen fixers colonize the root zones and fix nitrogen in loose association with plants. A very important bacterium of this category is Azospirillum which was discovered by Brazilian scientist, J. Dobereiner. In the late 1970s Azospirillum was found to enhance non-legume plant growth. In recent years, various other rhizobacteria such as Aeromonas veronii, Azotobacter sp., Azoarus sp, Cyanobacteria (predominantly of the genera Anabaena and Nostoc) Alcaligenas, Burkholderia, Comamonas acidororans, Enterobacter, Erwinia, Flavobacterium, rhizobia (including the Allorhizobium, Azorhizobium, Bradyrhizoblum, Mesorhizobium, Rhizobium and Sinorhizobium) Gluconacetobacter diazotrophicus, Herbaspirillum seroepdicae, Serratia, Variovorax paradoxus and Xanthomonas maltophilia have been identified for their use either as biofertilizers or biological control agents (Bioinoculants).

5 5 1.3 TYPES OF BIOFERTILIZERS There are various types of biofertilizers which are as follows: (a) Nitrogen-fixing biofertilizers: (i) Symbiotic nitrogen fixers - Rhizobium (ii) Non-symbiotic nitrogen fixers - Azotobacter - Azospirillum - Blue green algae - Azolla (b) Phosphorous mobilizing biofertilizers: (i) Phosphate solublizer - Bacillus - Pseudomonas - Aspergillus niger (ii) Phosphate absorber - VAM fungi (eg) Glomus, Gigaspora (c) Organic matter decomposer biofertilizers (i) Cellylolytic - Cellulomonus

6 6 - Trichoderma (ii) Lignolytic - Arthrobacter - Agaricus 1.4 POTENTIAL DEMAND OF BIOFERTILIZERS Since biofertilizers can successfully be used in all the crops grown under different agro-ecologies, their potential requirement is quite large and far exceeds the present production levels. The potential demand has been computed at 348 thousand tons with the assumption of biofertilizers application in 50% of the gross cropped area under different crops. It is also assumed that biofertilizers can substitute about 25% of the nutrient requirement of the crops. Depending upon the source of funding, biofertilizers production unit located in different states are grouped into two categories: Government of India (GoI) financed units and those financed by other sources. So far, 64 biofertilizer production units have been established with the GoI support. Those units have over 9000 tones of the total biofertilizers production. Remaining 38 biofertilizer production units with total installed production capacity (17,000 tons) is still very low (7.23%) composed to potential demand of 235 thousand tons for bacterial biofertilizers. This underlines the need for great efforts on expansion of biofertilizers network in the country.

7 7 1.5 CROP RESPONSE TO BIOFERTILIZERS Nitrogen is a key component of nutrients for plants. The current annual loss of arable land to soil degradation is estimated at 5 7 million hactare (Lal, 1989). Crop yields are often limited by nitrogen supply. Inputs of biologically fixed Nitrogen into agricultural systems are derived from symbiotic relationship between legume and Rhizobium, as well as due to non-symbiotic association between free living diazotophs and plant roots (Lata, 2002). Although indigenous population of Rhizobium are present in soil, they are not efficient in nitrogen fixation. For this purpose efficient and competent strains of Rhizobium are generally used as biofertilizers for legume crops. Globally about 11% of arable land is used to cultivate legumes, pulses and oil seeds (Peoples et al., 1995). Burns and Hardy (1975) estimated that a total of 175 million metric tons of Nitrogen per year, through biological Nitrogen fixation (BNF) of which legume N 2 fixation accounted for approximately 40%. BNF is an efficient source of Nitrogen (Peoples et al., 1995). In addition to Rhizobium, free living nitrogen fixers mainly Azotobacter, Azospirillum are blue green algae (BGA) also fix nitrogen and are used as biofertilizers for cereal crops and non-legumes. Azolla-Anabanea and Frankia also contribute towards soil Nitrogen. In phosphorus deficient soil phosphate slublizing microorganisms (PSM) and Mycorrhizae which solubilize and mobilize phosphorous to plants are considered to be important biofertilizers (Tilak, 2007). Biofertilizer improves soil particles and sustain soil fertility. It has been reported that the benefit to cost ratio of biofertilizer is fairly high, authors reported that biofertilizers barness atmospheric nitrogen and make it available directly to the

8 8 plant (Ganachitra, 2000). On the other hand it helps increasing phosphorous uptake by stining and releasing unavailable phosphorous. It enhances root proliferation due to release of growth promoting hormones (Subba Rao, 1993). Application of biofertilizers is known to improve the soil fertility and crop productivity in several crops. Improving the rice production can be achieved by breeding high yielding varieties and through optimizing the agricultural practices such as organic manures and biofertilizers application (Zaki et al., 2009). Increased yield of various legumes after inoculation with nitrogen fixing microorganism not only provide fixed nitrogen to plants but also provide Nitrogen status of soil (Zaidi et al., 2003). Field performance of manure from biogas plant has been found to increases the yield as well as soil microbial activity in maize (Mehetre and Kale, 2007). Biofertilizers have the potential of increasing the yields of legumes as well as reducing the use of cost of chemical nitrogen fertilizers. Biofertilizers, being biological in origin are relatively safe and sustainable. They are capable of supplying not only major nutrients but also micronutrients for effective growth of plants. Most of the biofertilizers are produced through involvement of microorganisms. Biofertilizers offer an economically attractive and ecologically sound mean of improving quality and quantity of internal sources. Biofertilizers are less expensive and improve crop growth and quality of crops by production of plant hormones (Dalve et al., 2009). Production and metabolism of phytohormones like auxins, cytokinins and gibberellins (Bottini et al., 2004) are among the mechanisms used by plant growth promoting rhizobacteria to promote plant growth.

9 Rhizobium Members of the Rhizobiaceae are among a special group of soil bacteria which have the unique ability to convert atmospheric dinitrogen into ammonia through the biological nitrogen fixation (BNF) process (Michiels and Vanderleyden, 1994). Rhizobia are mostly associated with legume roots (Freiberg et al., 1997), but occasionally found within the endorhizosphere of non-leguminous hosts (Yanni et al., 1997). It is estimated that the rhizobia-mediated BNF process contributes approximately 35 x tonnes, i.e., ca. 47% of the total N fixed annually to the global nitrogen budget. On an area basis, the Rhizobium legume symbiosis contributes Kg N per hectare per year (Elkan, 1992). The low cost of Rhizobium inoculants and high return from the BNF process are some of the reasons for the worldwide use of rhizobial inoculants for various legume crops (Shantharam and Mattoo, 1997). Legumes inoculation in soils containing native rhizobial population frequently results in small proportion of nodules by the introduced strain. Competitive strains of Rhizobium for chickpea, pigeon pea and mungbean have been identified by several workers (Sreekumar and Sen, 1987; Chauhan and Gaur, 1986; Saxena et al., 2002). Several pot and field trails were conducted under different projects at the Indian Agricultural Research Institute, New Delhi, India to demonstrate the responses of pulses and oil seed legumes to rhizobial inoculation. On an average, the yield increases were ranging from 32 to 61% depending on the crop Rhizobium strain, soil and agroclimatic conditions (Saxena, 2005).

10 10 The inoculation of Rhizobium which enhanced the nitrogen nutrition of the crop through symbiotic fixation of atmospheric nitrogen. Effectiveness of the symbiotic nitrogen fixation depends upon the proper establishment of interrelationship between a particular legume and a specific strain of Rhizobium (Dart et al., 1976). Variability among Rhizobium strain of the same species exists for biological nitrogen fixation (Khurana and Dudeja, 1981). Biological Nitrogen Fixation is the key to sustain agricultural productivity and a very important component of integrated plant nutrient system. Recent studies have established that Rhizobium, the well known nitrogen fixing root nodules endosymbiont of legume plants also develops a natural, beneficial endophytic association with cereal roots growing in the same crop rotation (Yanni et al., 1997) Azotobacter Azotobacter is a free living heterotropic nitrogen fixer is a beneficial rhizosphere of variety of plants. The genus Azotobacter has six species, viz. A. chroococcum, A. vinelandii, A. beijerinekii, A. nigricans, A. armemmacus and A. Paspoli. Except the last species, which is a rhizoplane bacterium, the other members are largely soil-borne and rhizospheric. The potential of A. chroococcum and A. paspali as a biofertilizers for various non-legume crops is well documented (Saxena and Tilak, 1998). Azotobacter species are known to influence plant growth through their ability to fix molecular nitrogen, production of growth promoting substance like IAA, gibberellins or gibberellins like compounds and vitamins, excretion of

11 11 ammonia in the rhizosphere in the presence of root exudates and production of antifungal metabolites (Singh, 2001; Paul and Verma, 2005). The beneficial effects of Azotobacter chroococcum are attributed to production of plant growth hormones improved nutrient uptake and antagonistic effect on plant pathogens (Yadav et al., 1994). The response of Azotobacter varied with crops, cultivars, agronomic practices, bacterial strain and interaction with native flora. Beneficial effects of Azotobacter chroococcum reported by various workers on different cereals, vegetables, oil seed and cash crops have been extensively reviewed by Saxena and Tilak (1998). Seed inoculation of Azotobacter chroococcum increases the yields of field crops by about 10% and cereals by about 15-20%. The response to inoculation was increased by manuring and by fertilizer application (Daterao and Lakhdive, 1992) Mycorrhizal Fungi The symbiotic associations of plant roots and fungi have intrigued many generations of biologists and in the late 1880s these associations were given the name Mycorrhiza. Vesicular arbuscular Mycorrhiza (VAM) is a mutually beneficial symbiosis or partnership between beneficial soil fungi and plants. The Arbuscular mycorrhizal fungi are all members of the Zygomycota and the current classification contains one order, the Glomales, encompassing six genera into which 149 species have been classified (Bentivenga and Morton, 1994).

12 12 The Arbuscular mycorrhiza (AM) is the most common of all mycorrhizal types involved and can benefit plant growth and health. The main benefit of mycorrhizae is the uptake of nutrients especially phosphorus. Phosphorus nutrition brings with it drought resistance and other benefits. They also benefit the cost plant by supporting growth regulating substances and vitamins and protecting against pollutants and soil-borne pathogens (Mitchell, 1993). Large number of experiments conducted in different parts of world confirmed the plant growth improvement due to inoculation with Vesicular Arbuscular Mycorrhizae (VAM). There is well documented evidence that VAM have important effects on plant phorphorous uptake and availability of other elements like zinc, copper, potassium, sulphur, aluminium, manganese, iron, etc. (Krishna and Bagyaraj, 1991) and cadmium (cd) (Guo et al., 1996) in areas beyond the root s depletion zone. Mycorrhizal fungi play a significant role in the formation of soil aggregate. The important role of the soil mycelium of mycorrhizal fungi in the formation of water stable soil aggregates is well documented (Miller and Jastrow, 2000). A well developed mycorrhizal symbiosis may enhance the survival of plants in polluted areas by better nutrient acquisition, water relations, pathogenic resistance, phytohormone production, contribution of soil aggregation, amelioration of soil structure and thus improved success of all kinds of bioremediation (Jeffries et al., 2003). Soil microorganisms influence the establishment and activity of Arbuscular mycorrhizal (AM) fungi. Interactions among mycorrhiza formation, nutrient

13 13 uptake and soil microorganisms (N 2 fixing bacteria, plant growth promoting rhizobacteria) have been reported as beneficial (Dey et al., 2005). Bacterial production of auxins can result in translocation of soluble sugars to the root which can enhance the metabolic activity of the fungus (Meyer and Linderman, 1986). Indian soils are mostly deficient in Nitrogen and phosphorous. Among Mycorrhizae, Vesicular arbuscular mycorrhizae (VAM) fungi are abiquitous and form obligate symbiotic associations with most families of crop plants. VAM have been shown to be beneficial to plants in better utilization of soil nitrogen (Marwaha, 1995), Phorphorous (Gerdeman, 1968), biological control of root pathogens, and uptake of mineral elements (Sukhada, 1998). VAM biofertilizers is a natural product carrying living microorganisms derived from the plant root or cultivated soil and has no harmful effect on fertility or plant growth (Marwaha, 1995). Mycorrhizal association in groundnut (Arachia hypogaea L.) was first reported by Butler in Later occurrence of the mycorrhizal fungi Gigaspora gigantia and Glomus macrocarpus in groundnut roots (Porter and Beute, 1972) and Glomus mossae in groundnut pegs (Graw and Rehme, 1977) was reported. The effect of Mycorrhizae in increasing plant growth has been well documented by different workers for many plant species. These fungi are also being recognized to influence soil development, as much as plant development.

14 14 Mycorrhizal fungi improve the soil phosphorous availability by solublizing inorganic forms of phosphorous by mineralization of organic phosphorus. Arbuscular mycorrhizae enhances water uptake particularly in nutrient deficient and dry soils (Auge, 2001). 1.6 ADVANTAGES OF BIOFERTILIZERS Biofertilizer provide essential elements like nitrogen, potash, phorphorous, sulphur, by directly supplying them or transforming them into soluble form; in addition, they also help plants to uptake several micronutrients. They supply some important enzymes, hormones and antibiotics that enhance crop growth and crop yield. Some biofertilizers protect plant against diseases, nematodes, drought, high temperature shock, high salinity. Biofertilizers are natural product carrying living microorganism derived from rhizosphere. As such no harmful effect on soil fertility is generally discernible. Soil born cellulose or lignin decomposing inoculants could produce high quality compost. Biofertilizers under optimum condition could enhance the crop yield by 10 20%. Use of biofertilizers is economical with a high cost: benefit ratio, without risk generally biofertilizer required in smaller doses.

15 15 Some biofertilizers may act as biopesticide. For example Azotobacter in strain has shown potential to inhibit seed borne pathogens of cereals. Besides their effect on current crop, use of biofertilizers also leaves considerable beneficial residual effect on soil fertility. 1.7 NEED FOR THE PRESENT STUDY Groundnut (Arachis hypogaea L.) is considered one of the most important oil crops in the world. Among the oil seed crop grown in India, groundnut occupies pre-dominant position. One of the reason of low yield of groundnut is the inadequate input of manures and fertilizers. Continuous use of inorganic fertilizers has resulted in ecological imbalance with consequent ill effects to the soil. In this case the use of biofertilizers is the biomanure capable of supplying nutrients from soil to plant system by their biological activity and maintenance of long term soil fertility and fostering soil biological activity. Hence the study is focused to The growth kinetics of Arachis hypogaea L. var. TMV-7 under the inoculation of biofertilizers with reference to physiological and biochemical studies. 1.8 OBJECTIVES The objective of the present study is to find out the role of biofertilizers like Azotobacter, Mycorrhizae and Rhizobium (mono, dual and combined inoculation) on Arachis hypogaea L. var TMV-7. To observe the morphological changes in germination percentage, growth and yield parameters.

16 16 To estimate the biochemical changes in chlorophyll, carotenoid, carbohydrate, sugar and enzymatic activities. To extract the oil from groundnut seed and estimate the physio-chemical properties of oil such as refractive index, saponification value, iodine value, peroxide value and free fatty acids. To analyze the protein content of groundnut seed by High Performance Liquid Chromatography (HPLC) method.