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Vol. 19 No. 1 - January 2013

Azotobacter chroococcum: A Potential Organism in the Management of Crop Yield
and Quality under Fly Ash Amendment

By: Nikita Parab1, Seema Mishra1 and S. R. Bhonde2

India is the sixth largest electricity generating and consuming country in the world. Coal is a principal commercial fuel source of energy for power production in India and it contributes about 70% of total electricity for domestic purposes. With the increasing demand of power, more and more thermal power stations are expected to be commissioned in near future. Thermal Power stations using pulverized or lignite coal as fuel generate large quantities of fly ash as a by-product. In India alone, the production of fly ash is reached to more than 200 MT/year in 2011-12 and is projected to be 300 MT/year in 2016-17. Thus, the managemaent of such a huge quantity of fly ash is of prime concern with regards to its disposal. Moreover, it is categorized as high volume low effect waste under Hazardous Waste (Management and Handling and Transboundary movement) Rules, 2008. Nearly 2000 million tons of fly ash accumulated over a period of time in ash ponds of different thermal plants occupies nearly 1,00,000 acres of land. The problem with fly ash disposal lies in the fact that not only ash leachates slowly, seep into ground water but also it remains air borne for a long period of time which further contaminates surface water as well as surface soil. With the commissioning of Fly Ash Mission by Government of India in the year in 1994 many projects focusing on the utilization of fly ash as raw material were initiated all over the country. So far a number of uses of this fly ash have been developed viz. substitute to cement in concrete, land filling, mine filling, agriculture etc. Practically fly ash consists of all the elements present in soil except organic carbon and nitrogen, thus it has been found to have a great potential material with manifold advantages in agriculture. Utilization of fly ash for agriculture purpose requires region wise extensive trials to identify suitable dose for a particular soil. It has been proved by several studies that the use of fly ash in agriculture provides a feasible alternative for its safe disposal to improve the soil environment and enhance the crop productivity.

Advantages of fly ash in agriculture

The utilization of fly ash in agriculture is proven helpful as it improves physical properties of soil hence fertility and crop yield to significant level. It alters the texture of soil such a way that it reduces bulk density, increases porosity, aeration and cation exchange capacity which increase water and nutrients holding capacity of soil. This retards the nutrient loss with water. Fly ash contains essential macro-nutrients like P, K, Ca, Mg and S and micro-nutrients including Fe, Mn, Zn, Cu, Co, B and Mo. The characteristic of fly ash to enhance the availability of soil nutrients to plants further attributes to increase value of chlorophyll and carotenoid pigments responsible in the process of photosynthesis. However, it also contains trace levels of Hg, Cd, Cr, Be, Pb, As, etc. Deficiency of organic carbon and nitrogen in fly ash can be fulfilled by addition of organic fertilizers and beneficial nitrogen fixing microbes. Among nitrogen fixing microbes Azotobacter is widely utilized as a biofertilizer along with fly ash amendment. It is proved to be beneficial in improving plant growth, yield and fertility of soil as well as nutrient status of crops under different levels of fly ash.

Azotobacter chroococcum : A nature friendly source of nitrogen

A. chroococcum is the most commonly occurring species in arable soils of India. It belongs to the family Azotobacteraceae. This family includes various gram negative, aerobic, heterotrophic, catalase positive, free-living diazotrophic bacteria present in neutral and alkaline soil. It fixes nitrogen directly from the atmosphere and releases it in the form of ammonia into the soil. It is categorized under plant growth promoting rhizobacteria (PGPR) as well as it also acts as biocontrol agent against phytopathogens and also well known to thrive under stress conditions. It is also evaluated for its potential of biodegradation of harmful waste products like organophosphate insecticide. Azotobacter has been found beneficial to a wide array of crops covering cereals, millets, vegetables, etc under different ago-climatic conditions. It has been also proved that Azotobacter inoculation curtails the requirement of nitrogenous fertilizers by 10 to 20% under normal field conditions.

When applied as seed treatment or as soil application, they multiply rapidly and develop a thick population in rhizosphere. They derive food from the oranic matter present in the soil and root exudates. The beneficial influence of Azotobacter on plant growth is attributed to improvement in seed germination and promotion of vegetative growth and root development. Apart from its ability to fix atmospheric nitrogen in soils, it can also synthesize growth promoting substances viz., auxins, gibberellins, cytokinins, vitamins to a little extent it, performs phosphate solubilization. Besides it also has a good potential as biocontrol agent for also management of phytopathogens, nematodes and insects by producing siderophore, antifungal compounds and defense enzymes. Hence Azotobacter is not only an eco-friendly source of nitrogen but also provides the growth promoting substances to the plant.

Potential of utilization of fly ash with Azotobacter

Fly ash is good source of plant nutrients; however it is deficient in nitrogen. Azotobacter not only helps to fulfill the demand of nitrogen but also improves the availability of other nutrients and enhances their uptake by the plants. The polysaccharides secreted by the Azotobacter can help to trap heavy metals present in fly ash and hinder their absorption by plants. Therefore, the combination of both fly ash and Azotobacter can reduce the demand of expensive chemical fertilizers which later show adverse effects on soil quality. Authors are standardizing the dosage of fly ash with Azotobacter as a source of nitrogen in onion with the support of Fly Ash Unit of DST, GOI. Some important observations and expected benefits are discussed herewith.

Fly ash as a carrier for biofertilizer

Fly ash has been recognized as a potential raw material as a carrier for Azotobacter formulations. The formulations of Azotobacter are available in various carrier and liquid based. However, these formulation materials add to the cost without giving any additional advantage to the soil and crops. Further, they deplete the natural resources. The application of fly ash as a carrier for Azotobacter is expected to be an effective way for its management in a useful manner and simultaneously, it will reduce the environmental pollution and cost of formulation material. Up to 50% of fly ash with soil and different organic fertilizers particularly vermicompost was found to be suitable in improving the density of bacterial cells and shelf life of Azotobacter. Application of fly ash based inoculum on seed or in soil would also improve the sticking and action of bacterial cells by providing porous surface.

Improvement in establishment, growth and yield of crops

Presence of majority of macro and micro nutrients in fly ash in sufficient amount makes it an efficient material for agriculture. Authors have observed good establishment, survival and less disease in kharif season onion crop when amended with fly ash and Azotobacter. Fly ash is rich in silica that is beneficial for plant growth, due, to overcome abiotic and biotic stresses by preventing lodging (falling over). Azotobacter has antifungal and antibacterial properties that increase resistance in plants against pests and diseases, as well as other stresses. Several studies have reported that 50 t/ha dose of fly ash significantly increases yield of some crops like wheat, rice, potato, maize, red gram, musturd, etc. Up to 40 % of increase was observed on inoculating Azotobacter with 50% chemical fertilizers in onion during rabi season at 50 t/ha dose of fly ash.

Improvement of soil physical properties and fertility

Management of agricultural sustainability requires optimal soil fertility and physical properties. It is reported earlier, combination of fly ash mixed with organic fertilizer, Azotobacter and 50% chemical fertilizer enhanced the fertility of soil and the water holding capacity, cation exchange capacity and availability of N,P,K, Ca, Mn, Zn was better in the soil than non- inoculated treatments. Fly ash also enhances soil bacteria count and enzyme activity of dehydrogenase, urease and alkaline phosphatase which are beneficial for plant growth. Azotobacter can survive at high dosage of fly ash even in the presence of heavy metals viz. Pb, Cd, As Cr etc. which could be due to their secretion of extra-cellular polysaccharide having protective roll against the toxic effects of these metals. Beneficial combined effects of flyash, organic fertilizers and Azotobacter on reduced heavy metal availability in soil could also be due to formation of complexes of heavy metals. Azotobacter spp. produces siderophores that binds iron, and molybdenum and controlling their concentration in soil.

Improvement in the nutrient uptake of crop

Fly ash is although rich in majority of macro and micronutrient but presence of heavy metals, may cause toxicity in product. In a study conducted by authors when the Azotobacter was amended in the presence of fly ash improvement in N, K, Ca and Zn in onion bulbs was observed during kharif season, with fly ash in comparison to chemical fertilizers. The secretion of plant hormones by Azotobacter enhances the uptake of many micronutrients by plants that improve their overall performance. At the same time levels of heavy metals viz. Cd, Cr, As, Pb, Hg were within permissible limit or below detectable limit.

Ancillary benefits

High efficiency of Azotobacter in atmospheric nitrogen fixation, phosphate solubilization and production of phytohormones and vitamins enables it to be used as a biofertilizer for enhanced plant growth. It has been observed that utilization of Azotobacter with fly ash could reduce the demand of chemical fertilizers up to 50%. Also, better association of AM fungi, phosphorus solubilizing microorganisms and actenomycetes was observed in the presence of Azotobacter that would further improve the sustainability of soil. Indirectly, it would also help in decreasing soil pollution, emission of CO2 to environment by inorganic fertilizer industries and the cost.

Epilogue

Integrated nutrient management (INM) is an integral part of the sustainable agriculture which requires the management of resources in a way to fulfill the changing human needs without deteriorating the quality of environment and conserving vital natural resources. Fly ash rich in many macro and micronutrients could be used as a substitute to chemical fertilizers. Its amendment in standardized dose with Azotobacter would improve the overall crop production and simultaneously, it will also facilitate an efficient and economic way to combat the problem of rising pollution by fly ash ponds.

1 SIES Indian Institute of Environment Management, Nerul, Navi Mumbai - 400 706, India, < seema.mishra03@gmail.com>

2 National Horticultural Research and Development Foundation, Nashik-Aurangabad Highway, District Nashik -422 001, India


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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