By Anju Bharti
It has become one of the greatest challenges to feed the increasing population of the world which is raising an alarm as the requirement of food will be 28.8 million tonnes, while the availability will be only 21.6 million tonnes by 2020 (Chandra Shekher Nautiyal, 2012). Soil, being a critical and important component on earth, not only used for sufficient food production but also for maintaining the sustainable global environmental conditions. In addition, it has an important role in various direct and indirect physicochemical and biological processes (Chandra Shekhar Nautiyal, 2012). The soil quality has been defined by many researchers as ‘the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain biological productivity, promote environmental quality, and maintain plant and animal health. Most of the activities like soil erosion, atmospheric pollution, extensive soil cultivation and grazing, salinisation and desertification decrease the productivity of agricultural land.
Agriculture, an integral and inseparable part of human civilisation, has always played a vital role in sustaining human life. The industrial revolution and technology, along with change of lifestyle, have played a pivotal role in changing the shape of agricultural values. The agricultural fertiliser has marked the new agricultural revolution in the light of scientific advances and has broken all records of productivity.
The chemical composition of different and essential minerals and elements meant for regular as well as growth and nourishment of all plants is termed as fertiliser. As these fertilisers have been used invariably to promote and enhance the productivity of commercial crops, therefore they are called agricultural fertilisers.
The increased use of chemical fertilisers in agriculture make a country self dependent in food production but at the same time it also deteriorates environment and causes harmful impacts on living beings. As fertilisers are not absorbed completely by plants, they seep into the water bodies through rain water which causes eutrophication in water bodies and affect living beings including growth inhabiting micro organisms. The excessive use of chemical fertilisers in agriculture are costly as well as having various adverse effects on soils i.e. depletes water holding capacity and fertility of soil. These were the reasons that led to development of low cost effective and eco-friendly fertilisers which work without disturbing nature. Now, certain species of micro organisms are widely used which have unique properties to provide natural products, and serve as a good substitute of chemical fertilisers.
Advantages of Agricultural Fertilisers
The proper usage of enhanced and modified fertilisers leads to a massive increase in agricultural productivity and net output. It strengthens the soil and enhances its fertility. There are numerous crops and plants which have different growing habits and nutrient requirements. The fertilisers help in fulfilling these needs and requirements of plants for maximum production.
The fertilisers are highly soluble and do not take much time to get dissolved in soil and reach the plant in no time. However, it happens only in the case of chemical fertilisers whereas organic fertilisers take time to get dissolved. Moreover, agricultural fertilisers are a combination of hazardous and beneficial fertilisers. Organic fertilisers are not as harmful as the inorganic ones; however, the former takes more time than the latter to reach the roots of concerned plants. Excessive fertilisation does encourage great yields however it also leads to air, water and soil pollution. Therefore, the fertilisers must be used in limited quantities and if possible organic and inorganic fertilisers should be used simultaneously to counterattack the miscellaneous soil hazards.
Today, biofertilisers have emerged as a highly potent alternative to chemical fertilisers because they are eco-friendly, easy to apply, non-toxic and cost effective nature. Biofertilisers make nutrients that are naturally abundant in soil or atmosphere, usable for plants and act as supplements to agrochemicals. Biofertilisers are best defined as biologically active products or microbial inoculants viz, formulations containing one or more beneficial bacteria or fungal strains in easy to use and economical carrier materials which add, conserve and mobilise crop nutrients in the soil. In other words, biofertiliser is a substance which contains living microorganisms which when applied to seed, plant surfaces, or soil, colonises the rhizosphere or interior of the plant and promotes growth by increasing the availability of primary nutrients to the host plant (Mazid et al, 2011a). Organic fertilisers contain organic compounds which directly or by their decay, increase soil fertility.
Biofertilisers may become commercially
promising in the long run by spreading massive awareness to producers and farmers mainly through utilisation and better communication. In India, government has been trying to increase the application of biofertilisers along with modern agrochemicals.
Biofertiliser: A Safe Alternative to Agrochemicals
A number of micro organisms (bacteria, fungi and algae) are considered as beneficial for agriculture and used as biofertilisers. Biofertilisers are supposed to be a safe alternative to chemical fertilisers to minimise the ecological disturbance. Biofertilisers are cost effective, eco-friendly and when they are required in bulk can be generated at the farm itself. They can increase the crop yield up to 10-40 percent and fix nitrogen up to 40-50 kg. The other plus point is that after using for 3-4 years continuously, there is no need of further application of biofertilisers because parental inoculums are sufficient for growth and multiplication. They improve soil texture, pH, and other properties of soil. They produce plant growth promoting substances IAA-amino acids, vitamins etc. They have 75 percent moisture and can be applied to the field directly. Biofertilisers contained 3.5-4 percent nitrogen, 2-2.5 percent phosphorus and 1.5 percent potassium. In terms of NPK, biofertilisers were found to be superior to farmyard manure and other types of manure (Mukhopadhyay, 2006).
Microbes used as Biofertilisers
Microbes are effective in inducing plant growth as they secrete plant growth promoters (auxin, abscisic acid, gibberellic acid, cytokinin, and ethylene) and enhance seed germination and root growth. They also play a considerable role in decomposition of organic materials and enrichment of compost.
Nitrogen Fixing Bacteria (Dubey, 2001):
Azotobacteracae: e.g. Azotobacter
Spirillaceae: e.g. Azospirillum and Herbaspirillum
Acetobacter diazotrophicus (Gahukar – 2005-06)
Cyanobacteria (Blue Green Algae)
Azolla: Anabaena Symbiosis
Limitations of Chemical Fertilisers (Agrilife, 2006)
Some fertilisers are more acidifying than others hence the need to use sparingly on low pH soils;
May contain heavy metals or salts which are hazardous;
Risk of erosion;
Excessive use may contaminate soil and waterways. The high solubility of chemical fertilisers also exacerbates their tendency to degrade ecosystems, particularly through eutrophication;
Sometimes do not replace trace mineral elements in soil which become gradually depleted by crops grown there. Hence, the need for use of micronutrients arises;
There are concerns though about arsenic, cadmium and uranium accumulating in fields treated with phosphate fertilisers;
Phosphate minerals contain trace amounts of these elements and if no cleaning step is applied after mining the continuous use of phosphate fertilisers, it leads to an accumulation of these elements in soil;
Use of fertiliser on a global scale emits significant quantities of greenhouse gases into atmosphere and has bad effects on anthropogenic climate change;
Few inorganic fertilisers are non-renewable in nature, like potassium and phosphorous which come from mines and are limited;
Due to increase in prices of chemical fertilisers and its scarcity led to look for the alternates.
Advantages of Biofertilisers
Activate soil biologically;
Biological control of soil pests and diseases;
Bridge gap between the need of Total Absorbable Nutrients of Agricultural Industry and availability of chemical fertilisers from fertiliser industry;
Cost effective, when compared to expensive chemical fertilisers;
Degrades organic residues into nutrients that can be absorbed by plants;
Direct or indirect supply of nutrients to plants;
Increase crop yield by 20-30 percent;
Restore natural soil fertility;
Stimulate plant growth;
Supplement to fertilisers.
Chemical fertilisers can be easily replaced by biofertilisers. But it can take place only slowly and gradually because sudden reduction will lead to reduction in crop yield. As our cropping systems are badly addicted to chemicals for getting instant nutrition, biofertilisers need time to establish in particular soil or ecosystem. Once they get established, they can easily replace it up to 50 percent chemicals under Integrated Nutrient Management System.
Due to indiscriminate and imbalanced usage of chemical fertilisers and harmful pesticides on crops, there is considerable reduction in soil health. Thus, there is a question on sustainability of agriculture systems which is likely to get collapsed. Dependence on chemical fertilisers for future agricultural growth would mean further loss in soil quality, possibilities of water contamination and unsustainable burden on the fiscal system. Consistent with current outlook, the Government of India aims not only to encourage the use of biofertilisers in agriculture but also to promote private initiative and commercial viability of production.
The high moisture content in biofertilisers may attribute contamination of micro organisms that either compete with biofertilisers or have antagonistic interaction. Retail shops do not sell biofertilisers because of short shelf-life, limited demand and lack of storage facilities. The reasons responsible for it are: lack of marketing infrastructure and distributing networks; ignorance of farmers about biofertilisers; absence of public support, and lack of assurance of higher benefits for retailers.
The Government of India has been trying to promote an improved practice involving use of biofertilisers along with other types of fertilisers. These may have multiple beneficial impacts on soil and can be relatively cheaper and convenient to use. Research and development efforts by the government and research organisations have brought remarkable progress in production and wide use of biofertilisers in the country; its potential requirement exceeds the actual production (Parr et al, 1990). Biofertilisers can act as a renewable supplement to chemical fertilisers and organic manures. They have the capacity to produce natural resistance in plants against pests and soil-borne diseases, because antibodies are produced and beneficial micro organisms participate in the soil to increase fertility (Board, 2004).
Excessive use of chemical fertilisers and pesticides to attain green revolution has made food and the environment contaminated and thereby putting ill effects on the health of living beings. Though the use of chemical fertilisers (nitrogen, phosphorus and potassium: NPK) enhance crop yield, it brings alteration in soil properties, functional diversity in microbial population and their enzymatic activities. Contrary to this, several researchers have demonstrated that organic farming (compost and green manure) leads to improved soil quality with higher microbiological activity involving crop rotation, reduced application of synthetic nutrients and no pesticides. The experiment with biofertilisers has proved that it can play a central role of soil resources for assuring food security and in increasing awareness for sustainable agriculture. Undoubtedly, if the use of these organisms is appropriately managed by farmers, it will help in effecting better well-being of crops, thereby, improving food safety.
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Dubey ( 2001). Precision farming - A new approach, Daya publishing company, pp 252-320.
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Kamal K Gangwar and Deepali (2013), Biofertilizers: An ecofriendly way to replace chemical fertilizers
Mukhopadhyay S, Deopura BL, and Alegirusamy R (2006), Journal of applied polymer science, Vol-10, issue 2, pg-838-842.
Nautiyal, Chandra Shekharl (2012), Microbes for Soil Sustainability and Crop Productivity, International society for environment botanists, Vol 18, no 3.
Parr JF, BA Stewart, SB Hornid and RP Singh, (1990). Improving the Sustainability of Dry Land Farming Systems. A Global Perspective. In: Advances in soil Science, Singh, RP, JR Parr and BA Stewart (Eds). Springer-Verlag Inc, New York, pp: 1-8.
http://www.somphyto.com/biofertilizer_compstudy.htm (Agrilife, 2006)