By Khurram Shahzad & Zeshan
THE rapid growth in population demands increased supply of food which can be optimised with larger use of inputs such as fertilisers. The use of nitrogenous, phosphoric and potassium fertilisers has become indispensable to attain good crops yield. At the same time, fertiliser prices are going up day by day due to energy crisis all over the world.
The Haber-Bosch process is generally used for the production of nitrogenous fertilisers worldwide, which, in addition to catalyst, requires high temperature up to 800 o F and pressure above atmospheric one. Therefore, industrial nitrogen fixation is heavily dependent on energy derived from fossil fuel which is depleting at a very fast rate and is getting costlier.
Fixation of molecular nitrogen can also be accomplished by a group of micro-organisms in soil and root tissues of certain plants in the presence of an enzyme “nitrogenase” under normal pressure and temperature that is dependent on energy from only renewable resources such as products of photosynthesis and organic materials in soil.
The nitrogenous fertilisers, applied at the recommended rates for getting higher yields, are also subjected to loss through various paths to environment and thus resulting in its pollution. Apart from this, hundreds of kilogrammes of solid waste are generated daily that can seriously affect the environment and human health, if not handled properly. This waste could be converted into useful products such as compost by providing favourable conditions for indigenous micro-organisms or by incorporating desired micro-organisms into it. So the strategy for improving agricultural production in developing countries should take into account the in-expensive, environment-friendly, realistic and programmatic approach.
The term biofertiliser or more approximately microbial inoculants can be defined as preparation containing live or latent cells of efficient strains of nitrogen fixing, phosphate solubilising or cellulytic micro-organisms used with an objective to increasing the number of these micro-organisms and accelerating certain microbial process to augment the extent of the availability of nutrients in the farms which can be easily assimilated by plants. The term biofertiliser is used for various types of materials such as composts, agro-waste, and some liquid cultures of unidentified miscellaneous microbes.
First of all, Nobbe and Hiltner introduced laboratory grown cultures of Rhizobia on solid media containing extracts of leguminous plants, gelatine, sugar, and asparagines in 1895. In the maiden attempt, 17 different inoculants for important leguminous crops were produced. The rhizobial inoculants (also known as legume inoculants) then became industrial proposition in the United States, Europe, Australia and India by the beginning of 20th century. In 1920 these got so popular that in the United States, besides the US Department of Agriculture and 20 research institutes, 17 commercial concerns were marketing inoculants. In Russia and Poland, non-symbiotic bacteria of one genus Azotobacter gained importance in the early part of 20th century. A product under the trade name Azotobakterin was prepared for soil and seed treatments and spectacular benefits were recorded on the yield of vegetables and cereals.
Following this success of legume inoculants, the biofertilisers for non legume crops are becoming increasingly popular in the world in recent years. Azotobactor inoculants are more common in the world because these can be applied to non-legume crops and promote seed germination and initial vigour of pants due to growth substances produced by the organism. In Pakistan, work on biofertilisers is being undertaken in different institutions like the University of Agriculture, Faisalabad, the Ayub Agricultural Research Institute (AARI) and National Institute of Biotechnology and Genetic Engineering (NIBGE). These have lunched their bio-products with different names like Rice Bioferts, Geraseemi Teeka, Biopower, etc.
Composting is a recycling process in which organic materials are biologically converted into amorphous and stable humus like substances under conditions of optimum temperature, moisture and aeration. It can be understood as a type of bacteria farming in which favourable environment is created for micro-organisms to thrive and multiply rapidly, accelerating the rate of decomposition of organic materials. It is the controlled decomposition and appropriate stabilisation of blended organic substrates under aerobic conditions that allows the development of thermophilic temperatures as a result of biologically produced heat, where organic material is decomposed to a level which could be handled, stored and applied to land without environmental impacts. So, composting provides a way to manage big volumes of organic waste in environmentally sound manners.
It has been estimated that about one kilogramme garbage per person is produced and disposed of daily in our country. In urban areas, less than 60 per cent waste is collected. No city in Pakistan has proper waste collection and disposal system. Bioconversion of that organic waste is one of the major options, which could be effective for reducing huge piles of organic wastes and cleans the environment.
Compost is made from mixing together organic waste materials – such as leaves, farmyard manure, poultry manure, sugarcane filter cake, weeds and straw – and leaving them to decompose until a black, crumbly soil is formed. The materials needed to make it are locally available and accessible. Composting provides a way not only of reducing the amount of waste that needs to be disposed of, but also of converting it into a product that is useful for agriculture, gardening, landscaping, or house plants. Recycled organic wastes cannot only act as supplement to chemical fertilisers but may also improve the physio-chemical properties of soil
Although composting is an old technique, efforts have been made to improve it with respect to quality of compost and rate of composting. Heightened environmental awareness has sparked renewed interest in composting. With the resurgence of interest in this technology, efforts have been made to improve it with respect to rate of composting and quality of the end product. Manipulation of moisture content, pH, nutrient content ratio and oxygen supply not only increases composting rate but is also helpful in achieving the product of desired characteristics. A novel approach could be that composted material may be converted into value-added product such as an effective biofertliser by blending plant growth promoting rhizobacteria (PGPR) which are free living soil bacteria that can either directly or indirectly facilitate rooting and growth of plants. Moreover, incorporation of compost with PGPR could make it a promising biofertilizer.
There are several mechanisms by which the PGPR affects plants’ growth such as their ability to produce various compounds (such as phytohormones, organic acids, siderophores), fix atmospheric nitrogen, solubilise phosphate and produce antibiotics that suppress deleterious rhizobacteria, and produce biologically active substances or plant growth regulators. Production of biologically active substances or plant growth regulators is one of the major mechanisms through which PGPR influences the plant growth and development.
Plant growth regulators are the organic compounds which even at low concentration have shown far-reaching effects on growth and development of plants. Therefore, direct use of micro-organisms to promote plant growth continues to be an area of rapidly expanding research and is currently attracting considerable attention of the microbiologists to increase growth and yield of crop plants. The use of PGPR to enhance plant growth and crop yield is predicted to become an emerging trend in contemporary agriculture in the near future.
Several researchers of the world have reported the effect of biofertilisers or compost for improving growth and yield of various crops which are being highlighted here. Some Pakistani scientists in 1996 conducted a field experiment to study the effect of azotobacter inoculation on growth and yield of wheat (cv. Inqab) in the presence of NPK (150-25-50). The data revealed that seed inoculated with various azotobacter cultures significantly increased grain yield (38.5 per cent), straw yield (15.3 per cent), number of tillers (12.5 per cent), spikelets (10.7 per cent) and 1000-grain weight (7.3 per cent) compared with un-inoculated control.
Some scientists compared the effect of traditional commercial fertiliser, compost and barnyard manure. According to their results of a two-year field experiment of wheat, compared to the control, the increases of the grain yield by the application of commercial fertiliser, different doses of compost and barnyard manure were observed as 21 per cent, 18-29 per cent and 32 per cent, respectively.
The biofertiliser or compost enriched with nutrients, plant growth regulators or PGPR can be used to increase per unit yield of crops on sustainable basis. This approach can help us to obtain high yield potential on one hand and reduce dependence on chemical fertilisers on the other hand without compromising per unit yield. This environment- friendly strategy can also help in tackling the pollution problem created due to the piling up of huge volumes of poisonous organic wastes.
The following considerations can be helpful in future for development of biofertlisers: Finding out keys to specificity of nitrogen fixing organism to selected plants; acquiring the property of nitrogen fixation by other non-nitrogen fixing micro-organism; evolving nitrogen-fixing plants; exploiting other plant-micro-organism associations; efficiently exploiting the non-biological systems of nitrogen fixation, and recycling of wastes for utilising nutrients.