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Vol. 17 No. 2 - April 2011

Liquid Biofertilizers: Advantages Over Carrier Based Biofertilizers

for Sustainable Crop Production

By: M. Verma*, S. Sharma*, R. Prasad*

As the disadvantages of the use of chemicals in agriculture have been noticed in recent years, a search for alternatives for chemical fertilizers and pesticides has started throughout the world. The use of chemical fertilizers as well as pesticides is much more in developing countries as compared to developed countries. Organic farming is the only alternative to get rid of chemical fertilizers and synthetic pesticides. There is increasing awareness about organic agriculture practices in the world. Organic agriculture is the growing food without pesticides and fertilizers. Organic production is a system of farming that restores, maintains and enhances ecological balance.

What are the alternatives for chemical farming?

Biofertilizers have been identified as alternative to chemical fertilizers to increase soil fertility and crop production in sustainable farming. There are abundant microorganisms thriving in soil, especially in the rhizosphere of plants. It is well known that a considerable number of bacterial and fungal species possess a functional relationship and constitute a holistic system with plants. They are able to exert beneficial effects on plant growth. Application of beneficial microbes in agricultural practices started about 50 years ago and there is now anincreasing evidence that these beneficial microbial populations can also enhance plant resistance to adverse environmental stresses, e.g. water and nutrient deficiency and heavy metal contamination.

What are biofertilizers?

Bio-fertilizers are natural fertilizers which are microbial inoculants of bacteria, algae, fungi alone, or in combination, and they augment the availability of nutrients to the plants. The use of bio-fertilizers, in preference to chemical fertilizers, offers economic and ecological benefits by way of soil health and fertility to farmers. These are products containing living cells of different types of microorganisms, which have the ability to convert nutritionally important elements from unavailable to available form through biological processes. They are involved in symbiotic and associative microbial activities with higher plants. These are natural mini-fertilizer factories that are economical and safer source of plant nutrition for increasing the agricultural production and improving soil fertility. The microorganisms colonize roots of rice, wheat, maize, sugarcane and form root nodules in leguminous plants. Different biofertilizers have shown nitrogen fixing, phosphorus solubilizing and phytohormone producing abilities that are used for increasing the agricultural productivity, e.g. (Bradyrhizobium for legumes (grain, fodders), plant growth promoting rhizobacteria (PGPR) for cereals (wheat, rice, grasses etc.), Azolla for rice ecosystem, and actinomycetes (Frankia spp.) for forest trees. These microorganisms convert atmospheric nitrogen to plant usable form and can provide up to 200 kg N/ha/crop. Next to nitrogen, phosphorus is essential for crop production. Although our soils have sufficient phosphorus but this phosphorus is not available for plants and most (>90%) of our soils are phosphorus deficient. Usually the pH of our soils is more than 7.5 and at this pH, very low amount (3-10 mg/ kg) of phosphorus is in available form. In such soils, when phosphatic fertilizers are added only a part of it is utilized by the plants and remaining part is precipitated due to the presence of calcium and with time it is converted into highly insoluble forms of calcium. In recent years, biofertilizers have emerged as an important component of the integrated nutrient supply system and hold a great promise to improve crop yields through environmentally better nutrient supplies. However, the application of microbial fertilizers in practice, somehow, has not achieved consistent results.

A group of bacteria referred to as plant growth-promoting rhizobacteria (PGPR), which participate in many key ecosystem processes such as those involved in the biological control of plant pathogens, nutrient cycling and seedling establishment, and, therefore, deserve particular attention for agricultural or forestry purposes. PGPR may colonize the rhizosphere, the surface of the root, or even superficial intercellular spaces of plants. It has been revealed that the effect of nitrogen fixation induced by nitrogen fixers is not only significant for legumes, but also non-legumes. Moreover, some strains have multiple functions for plant growth. Phosphate (P) and potassium (K)-solubilizing bacteria may enhance mineral uptake by plants through solubilizing insoluble P and releasing K from silicate in soil. Soil microorganisms are important components in the natural soil sub ecosystem because not only they contribute to nutrient availability in the soil, but also bind soil particles into stable aggregates, which improve soil structure and reduce erosion potential.

Advantages of biofertilizers over chemical fertilizers

The utilization of microbial products has several advantages over conventional chemicals for agricultural purposes. Microbial products are considered safer than many of the chemicals now in use, neither toxic substances nor microbes themselves will be accumulated in the food chain, self-replication of microbes circumvents the need for repeated application, target organisms seldom develop resistance as is the case when chemical agents are used to eliminate the pests harmful to plant growth and properly developed biocontrol agents are not considered harmful to ecological processes or the environment.


Azotobacter is a free-living, gram negative, aerobic, nitrogen-fixing bacterium and is therefore being used as biofertilizer to replace chemical fertilizers. It grows from 28 30 0C and a pH range 7.0 to 7.5. It uses sugars, alcohols and salts of organic acid for growth. Generally it fixes non-symbiotically about 10 mg of atmospheric nitrogen/gm of carbohydrates (usually glucose) consumed. It is non-spore forming but can form cyst in adverse conditions and in older cultures grown with sugar as the carbon source. Cyst has a characteristic structure a central body surrounded by a cyst coat, consisting of an exocystorium and an exine. Cysts accumulate poly B- hydroxyl butyric acid (PHB). With the onset of favourable conditions they give rise to vegetative cells. On nitrogen free agar medium with sugar as carbon source colonies appear within 48 hr at 30 0C. The colonies are smooth, opaque, low convex and viscid.

Azotobacter biofertilizers

Azotobacter biofertilizers contain very high number of live Azotobacter bacteria. It can be used in any non-legume crop of short, medium and long duration. Besides fixing nitrogen these bacteria secrete certain growth promoting hormones such as indole acetic acid, gibberellic acid and cytokinins, which promote vegetative growth and root development. Azotobacter cultures used as inoculants have been reported to produce gibberellic acid, indole 3-acetic acid and cytokinin, which may promote seedling development and plant growth. The potential use of Azotobacter spp. was reviewed by Brown (1982), who concluded that inoculation with A. chroococcum occasionally promoted yields, probably by mechanisms other than biological N fixation.

Carrier-based biofertilizers

Carrier-based biofertilizers are prepared with the help of activated charcoal, which act as a carrier for microbial inoculants. Biofertilizer consumption is not very satisfactory due to certain disadvantages associated with carrier-based biofertilizers like low shelf life (3-4 months), storage condition (stored in cool temperature) as it is temperature sensitive, bulky to transport, therefore, high transport cost, less scope for export, more chances of contamination, problem of proper packing, poor cell protection, poor moisture retention capacity and restriction on use of charcoal as a measure of conservation.

Liquid Biofertilizers: solution to carrier based biofertilzers

The strength of biofertilizers is determined by two basic parameters 1. Number of cells 2. Efficiency of the microorganisms to fix nitrogen or solubilize phosphates. Liquid biofertilizers are liquid formulation containing the dormant form of desired microorganisms and their nutrients along with the substances that encourage formation of resting spores or cysts for longer shelf life and tolerance to adverse conditions. The dormant form on reaching the soil, germinate to produce fresh batch of active cells. These cells grow and multiply by utilizing the carbon source in the soil or from root exudates.

The advantages of liquid biofertilizers over conventional carrier based biofertilizers are: longer shelf life (12- 24 months), no effect of high temperature and no contamination, no loss of properties due to storage at high temp. up to 450 C, high populations can be maintained more then 109 cells/ ml up to 12 to 24 months, easy to use by the farmers, high export potential, dosages are 10 times less then carrier-based, quality control protocols are easy and quick. Lot of work has been done on carrier-based biofertilizers in the context of organic food production. In view of the advantages of liquid biofertilizers over carrier based formulations, research has now been started on the production and testing of liquid biofertilizers.

Center for Rural Development and Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, [email protected]

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

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