Plant Acclimation to Environmental Stress || Biofertilizers: A Sustainable Eco-Friendly Agricultural Approach to Crop Improvement

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  • 403N. Tuteja and S. Singh Gill (eds.), Plant Acclimation to Environmental Stress,DOI 10.1007/978-1-4614-5001-6_15, Springer Science+Business Media New York 2013

    1 Introduction

    Both the quality and quantum of agricultural production is dependent on the quality of soil. Soil is not only an important resource for the farmer but it also provides niche to the various organisms from microbes to mammals. Globally, the loss in crop productivity has been caused due to a poor management of top soil. Excessive exploitation of arable land without suf cient addition of useful nutrients as well as the detriment caused by salinization and drought has been known to be the chief reason for the poor quality of soil (Yuan et al. 2007 ) . Hence the proper maintenance of soil is a key to crop productivity. Chemical fertilizers serve as the best and often a too convenient method to enrich soil with useful nutrients and to meet the global demands of food production; however, they are economically very expensive and hazardous to health (Righi et al. 2005 ) . Fortunately, nature has provided innate machinery consisting of various microbes and useful ora of the soil to answer this challenge. This machinery not only maintains the richness of the soil but it also works in tandem with plants as part of an ecosystem. This machinery is what con-stitutes biofertlizers and is a central part of what we know as green agriculture.

    Biofertlizers are the preparations containing ef cient strains of micro-organisms, organic products and dead tissues of plants which give nutrients to the soil as well as plants. It gradually enhances soil fertility and increases crop yield. Biofertlizers convert unavailable form of nutrients to available form by increasing the microbial population in the rhizosphere. Microbial populations are responsible for the supply of soluble nutrients to the plants. They are useful in various ways that includes

    R. K. Sahoo D. Bhardwaj International Centre for Genetic Engineering and Biotechnology (ICGEB) , Aruna Asaf Ali Marg , New Delhi 110 067 , India

    N. Tuteja Plant Molecular Biology, International Centre for Genetic Engineering and Biotechnology (ICGEB) , Aruna Asaf Ali Marg , New Delhi , India

    Chapter 15 Biofertilizers: A Sustainable Eco-Friendly Agricultural Approach to Crop Improvement

    Ranjan Kumar Sahoo , Deepak Bhardwaj, and Narendra Tuteja

  • 404 R.K. Sahoo et al.

    xing of atmospheric nitrogen and solubilization of plant nutrients like phosphorus and sulphur. Microbiota also stimulates plant health by suppression of disease, deg-radation of contaminants and promotion of plant growth through synthesis of growth-promoting substances, like auxins and cytokinins, and also provides protec-tion against biotic and abiotic stresses (Pedraza 2008 ; Sturz and Christie 2000 ; Kader et al. 2002 ) . Preparations containing these can also be considered as fertiliz-ers under a broad term, microbial fertilizers.

    The commercial history of biofertilizers began with the launch of Nitrogin by Nobbe and Hiltner, bacterial inoculants for legumes in 1895. Timonin ( 1948 ) pre-pared bacterial inoculants named Alnit from the mixture of useful bacteria and compost. This proved ef cient for the growth of non-leguminous crops. These bac-teria were identi ed to be common anmoni ers. The discovery of Clostridium and Azotobacter opened a new eld for the search of cheap bacterial fertilizer (Ashby 1907 ) . Ghosh ( 2000 ) reported that the use of biofertilizer alone showed signi cant improvement in plant height and number of tillers per plant. The rhizo-sphere of plants contains various species of soil bacteria which may stimulate plant growth by various and different mechanisms. These bacteria are collectively known as plant growth-promoting rhizobacteria (PGPR). One of the mechanisms by which they function is through xing of atmospheric N 2 , which increases the availability of usable form of N 2 in the rhizosphere and which in turn helps in the better growth of plant roots. They are also known to increase the yield attributes and seed yield over control. They also promote bene cial plant and microbe symbiosis and there-fore are more widespread and utilized as biofertilizers. However, not all the PGPR are utilized as biofertilizers.

    In this chapter PGPR that include different types of biofertilizers, microbes involved in it and their impact on different crops have been described; in the last we have described the various mechanisms that are involved in the activity of PGPR (Table 15.1 ). The various biofertilizers which are described are Azotobacter , Azospirillum , Rhizobium , Blue green algae, phosphorus and potassium solubilizing micro-organisms (KSM), mycorrhizae and vermicompost.

    2 Plant Growth-Promoting Rhizobacteria

    PGPR are naturally occurring soil bacteria that remain in the vicinity of roots of plants for the safety and availability of nutrients to the plants. There is a symbiotic relationship between these bacteria and plants. The plethora of micro-organisms that bene t plants is termed as PGPR; they in uence their growth in many ways. In any given situation plants cannot grow in isolation, they require micro-organism to support their life and vice versa (Doyle 1998 ) . It has been seen that certain strains of PGPR help in the improvement of biomass either in root or shoot growth (Karlidag et al. 2007 ) . They not only help plants in providing the necessary condi-tions for easy uptake of nutrients but also help them in defending themselves from attack of various pathogens. Moreover, they help plants in combating various biotic

  • 40515 Biofertilizers: A Sustainable Eco-Friendly Agricultural Approach

    Table 15.1 List of growth promoting rhizobacteria and their relation to host plants

    Name of PGPR Function Crops Relationship to host References

    Azotobacter sp. Nitrogen xation

    Wheat, Oat, Barley Mustard, Seasum Rice, Linseeds, Sun ower Castor, Maize, Sorghum Cotton, Jute, Sugarbeats Tabacco, Tea, Coffee Rubber, Coconuts

    Free-living Burgmann et al., ( 2003 )

    Azospirillum sp. Nitrogen xation

    Potato, Radish, Spinach Turnip, Carrot, Perwal Onion, Brinjal, Cauli ower,

    Cabbage Tomato, Chillies, Pearl

    millets, Fingermillets Kodomillet, Rice, Wheat,

    Oat, Barley

    Free-living Kanan et al. (2010), Dobereiner and Day, ( 1976 ) and Lakshmi-kumari et al. ( 1976 )

    Rhizobium sp. Nitrogen xation

    Chickpea, Pea, Groundnut, Soyabean, Beans, Lentil, Lucern, Berseem, Green gram, Black gram, Cowpea, Pigeon pea

    Symbiosis Bajpai et al. ( 1974 )

    Bacillus sp. Phosphorus/Potash

    Solubilizer

    Cotton, Jute, Banana, Potato Free-living Sheng and He ( 2006 )

    Aspergillus sp. Phosphorus/Potash

    Solubilizer

    Black gram, Ground nut Free-living Kundu and Gaur ( 1980 )

    Penicillium sp. Phosphorus Solubilizer

    Green gram, Soyabean Free-living Kucey ( 1988 )

    Tolypothrix Nitrogen xation

    Rice Symbiosis Kaushik ( 1998 )

    Scytonema Nitrogen xation

    Rice Symbiosis Kaushik ( 1998 )

    Nostoc Nitrogen xation

    Rice Symbiosis Kaushik ( 1998 )

    Anabaena Nitrogen xation

    Rice Symbiosis Kaushik ( 1998 )

    Plectonema Nitrogen xation

    Rice Symbiosis Kaushik ( 1998 )

    Ectomycorrhiza Phosphorus uptake

    Chickpea, mungbean, wheat Rice, Sorghum, Barley,

    Onions, Cowpea, rubber Coffee, Sugarcane

    Symbiosis Lamabam et al. ( 2011 ) , Singh et al. (1991)

    Endomycorrhiza Phosphorus uptake

    Chickpea, mungbean, wheat Rice, Sorghum, Barley,

    Onions, Cowpea, rubber Coffee, Sugarcane

    Symbiosis Lamabam et al. ( 2011 )

  • 406 R.K. Sahoo et al.

    and abiotic stresses (Saravanakumar et al. 2010 ) . The various advantageous effects of PGPRs are ef cient seed germination, plant height, increased chlorophyll con-tent and nodulation in legumes (Holzinger et al. 2011 ; Tittabutr et al. 2008 ) . They ensure the availability of certain important macronutrients that includes nitrogen, phosphorous, sulphur, iron and copper. They help in the induction of various growth regulators (Ahmad et al. 2008). They enhance the growth of other bene cial bacteria and fungi.

    Some of the PGPR that have been identi ed in the last few years and that add to the natural ora of soil to change complex matter into simple and usable form are Arthrobacter, Alcaligenes, Azospirillum, Azotobacter, Bacillus, Burkholderia, Enterobacter, Klebsiella, Pseudomonas, Serratia, etc. We can further classify these PGPR into bio-protectants, bio-stimulants and biofertlizers. Some of the organisms that have been used at commercial level as bio-protectants are Bacillus , Streptomyces , Pseudomonas , Burkholderia and Agrobacterium . Bio-protectants induce SAR and production of siderophore. SAR is one of the methods that plant acquire to protect themselves. PGPR triggers defence-related genes with or without the involvement of SA and MeJA (Zhang et al. 2002 ; Sjoerd et al. 2009). The up-regulation of defence-related genes suppress the growth of deleterious micro-organisms that affects the growth of plants.

    3 Types of Biofertlizers

    4 Nitrogenous Biofertilizer

    Nitrogen (N 2 ) is a key component of the constituents of life such as DNA, RNA, vitamins, hormones, proteins and enzymes which regulate the various metabolic processes. The application of nitrogen to rice in particular in uences crop yield in different ways. For example, the addition of nitrogenous fertilizer increases the leaf area, tiller formation, photosynthetic productivity, etc., which in turn improves the biomass, grain yield and quality of production (Lampayan et al. 2010 ; Jiang et al. 2008 ) . De ciency of nitrogen is one of the current problems in agricultural soils (Abrol et al. 1999 ) . Nitrogen is signi cant for rice in the initial days of its cultiva-tion. Moreover, rice requires 1 kg of nitrogen to produce 1520 kg of grain. In the tropics, lowland rice yields 23.5 Mg/ha using naturally available N 2 derived from biological nitrogen xation (BNF) by free-living, plant-associated diazotrophs and from mineralization of soil N 2 . Nitrogen-rich food is still the most favourite among consumers and its management is necessary for sustainable agriculture and food security (Spiertz 2010 ) . Presently, higher yields are necessary to support the unprec-edented growth in population. During the green revolution and since the 1960s, the application of nitrogenous fertilizers boosted rice yields by 200.5 million tonnes to match increasing demands (Lin et al. 2009 ) . In the next 25 years, production will have to increase by nearly 70% more than the 460 million Mg harvested (IRRI 1993).

  • 40715 Biofertilizers: A Sustainable Eco-Friendly Agricultural Approach

    Enhancing rice production from the present 812 Mg/ha in 2020 (Green Revolution 2) would require an increase in fertilizer application from 220 to 400 kg/ha. At current levels of N 2 use ef ciency, it would require approximately double the volume of 10 million mg of nitrogenous fertilizer. It is in this context that biofertilizer-derived BNF gained importance.

    4.1 Nitrogen Fixation Systems and Organisms

    Nitrogen xation is the conversion of atmospheric nitrogen (N 2 ) to ammonia (NH 3 ). Nitrogenase is the key enzyme for biological nitrogen xation, which is possessed by diverse group of micro-organisms. Nitrogenase catalyses the reduction of nitrogen gas to ammonia in the absence of oxygen (Fig. 15.1 ). In the natural habitat the biological N 2 - xation is the most important source of nitrogen. Many bacteria and archea bacteria can x biological nitrogen. It is estimated that free living nitrogen xing prokaryotes (Table 15.1 ) of soil x approximately 60 kg/ha nitrogen in a year (Burgmann et al. 2003 ) . Biological N 2 - xation is gaining importance in the rice ecosystem because of environ-ment degradation caused by the excessive usage of nitrogenous fertilizers to increase rice productivity. Thus, biological xation of atmospheric N 2 , especially non-symbi-otic N 2 - xation in the soil, has drawn the attention of various agriculture scientists in recent decades especially for improving the plight of agriculture.

    Azotobacter , Azospirillum and Rhizobium play a signi cant role in supply of atmo-spheric nitrogen to plants. In other words they help in the availability of atmospheric

    Fig. 15.1 Model to show the reduction of atmospheric nitrogen to ammonia by nitrogenase enzyme. N, Nitrogen; H, Hydrogen; and NH 3 , Ammonia

  • 408 R.K. Sahoo et al.

    nitrogen available that is about 80,000 exact term over a hectare of land. Ef cient strains of Azotobacter and Azospirillum and Rhizobium x nitrogen signi cantly in comparison to inorganic fertilizers, and help in plant growth. In addition to N 2 - xation, they are supposed to promote the physiology of plants (Table 15.2 ) or improve the root morphology of the rice plant (Choudhury and Kennedy 2004 ) .

    4.2 Azotobacter as Ef fi cient Nitrogen Fixer

    Azotobacter is usually an aerobic, free-living, motile, oval or spherical gram negative (ve) soil bacteria, which produce capsular slime (Tejera et al. 2005 ) . An obligate diazotroph soil-dwelling organism is used by one of the important steps of nitrogen cycle with wide variety of metabolic capabilities, which include the capability to x atmospheric nitrogen by converting it to ammonia (Gaur 2006 ) . There are different strains of Azotobacter which can be distinguished on the basis of chemical and bio-logical characters. However, some strains have higher nitrogen xing capability than others (Burgmann et al. 2003 ) . Azotobacter chlorococcum is a commonly occurring species of Azotobacter that can be found in most of the agricultural lands; however, Azotobacter is less versatile in the rhizosphere of crop plants and unculti-vated land. Azotobacter is used as a biofertilizers for different economically impor-tant plants like wheat, oat, barley, mustard, sesame, rice, linseeds, sun ower, castor, maize, sorghum, cotton, jute, bajra, sugar beats, tobacco, sugarcane, tea, coffee, rubber and coconuts (Table 15.1 ).

    Besides nitrogen xation, Azotobacter also produces thiamine, ribo avin, indole acetic acid (IAA) and Gibberellins (GA). Azotobacter when applied to seeds can improve seed germination to a considerable extent; moreover, owing to its anti-fungal nature it also protects young seedlings from being attacked by fungal patho-gens. It also releases vitamins and phytohormones that help plants in combating plant diseases; therefore it plays an important role in biotic stress tolerance (Kader et al. 2002 ) . Azotobacter was also found to possess glucose d...

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