USING BIO-FERTILISERS FOR HEALTHY FOODS
PROF DR. SM ALAM
May 17 - 23, 2010
Bio-fertilisers or bioorganic farming offers the potential solution to the various problems facing the current agricultural practices.
Bioorganic farming works in harmony with the natural system. It encourages and enhances biological cycles within the farming system, furnishes conditions of life that allow all possible genetic diversity of agricultural system and its surroundings including the protection of plants and wildlife habitat by furnishing conditions of life that would allow all life forms to perform freely.
The choice is the choice of material, substances and/or practices, which are the least environmentally disruptive both at the micro and macro levels.
The world population is increasing tremendously and food production continues to decline. Drought, salinisation, unavailability of inputs and inappropriate utilisation of resources are the main reasons that add to food shortage. Low-cost nitrogen is one of the requisites for the small rice farmers of the tropics and subtropics. Two events have stimulated research to provide low-income rice farmers with lower cost nitrogen for their rice fields. First, energy shortages have increased nitrogen fertilisers costs, second the efficiency of utilisation of applied nitrogen by rice is markedly influenced by timing and placement of the applied nitrogen.
With the increasing population growth rates, there will be an increased pressure on the agricultural lands for producing more food. Even marginal lands are put to production and most demand now is directed to rain fed agriculture for more output through fertilisers.
FAO has reported that up to 50 per cent of the growth in crops production that was witnessed in developing countries during the last four decades was due to the used chemical fertilisers. The fertilisers use rate in some of the countries of the region are among the highest worldwide. In Egypt, for the example the national average for fertiliser consumption was 347 kg/ha, Saudi Arabia 336 kg/ha, Pakistan 73 kg/ha, while USA's consumption is 42 kg/ha and world average is 28 kg/ha. Huge quantities of fertilisers are applied annually to soils over the world: 22 billion metric tons fertilisers, in addition to 16 million metric tons of herbicides, 18 million metric tons of insecticides and 12 million metric tons of fungicides).
All these chemicals that are taken by plants are absorbed from the soil, volatilise in the air or leached down with drainage water, join the groundwater and cause pollution.
High levels of nitrates are very common in irrigated agriculture especially with intensive agriculture related to surface irrigation and high fertiliser rate there is a matter of concern in Pakistan, as it is one of the countries consuming very large amounts of nitrogen per unit area. There are estimates that the use of nitrogen fertilisers will continuously increase till the year 2010.
Optimising the use of fertiliser and minimising losses will help increasing the yield ensuring high quality, decreasing environmental hazards and probably will help the fertilisers industry to have a surplus production for export. The World Health Organization (WHO) estimates that around one million chemical compounds are used worldwide and millions of tons of these chemicals are used annually on our lands. In US alone, it was estimated that about 60,000 newborn children are with some mental/physical retardation due to pesticides used during the last 50 years.
Bio-fertilisers are microbial preparations which supply nutrients especially nitrogen and phosphors to crops. Rice has been grown for ages in several parts of the world. There are about 100 million hectares of paddy fields in the world and it constitutes nearly 20 per cent of the total world food grain production. On the other hand, rice is considered a primary or secondary staple food for nearly 3.5 billion people; most of them are poor and live in developing countries.
As bio-fertilisers blue-green algae and Azolla are important groups of microorganisms capable of fixing atmospheric nitrogen, they grow most abundantly in tropical and subtropical regions and are common in flooded rice paddy soils. Their possible role is the nitrogen accumulation in soil and providing the growing rice plants with considerable amounts of fixed -N. Blue-green algae represents a sell-supporting system of carrying out both photosynthesis and biological nitrogen fixation.
The energy requirement for the latter process is being provided by the Sun. The amount of nitrogen fixed by blue-green algae (BGA) depends on the algal species as well as physiological and environmental conditions. The amount of nitrogen fixed by blue-green algae under laboratory condition varies markedly according to the algal species, the type of medium, incubation period, and growth condition. These amounts ranged between 22-270 mg/100 ml medium whereas, the amount of nitrogen fixed by BGA under field conditions ranges between 15-80 kg/ha according to algal species, fertilisation, soil and environmental conditions. Blue-green algae liberates large quantities of ammonia as well as a variety of organic compound and some growth promoting substances.
Azolla grows vigorously in drainage canals, ponds, paddy fields and stagnant pools of rivers and widely distributed in tropical and temperate zones. Azolla contains in the cavities of its leaflets filamentous BGA called Anabaena azollae. It contains 3-4 per cent dry mass & 4-5 per cent nitrogen. Azolla may grow at a temperature of 14-30oC with optimum 25-30oC. The doubling time of Azolla varies depending on the species and growth condition. Azolla anabaena symbiosis has proven to be effective also as a source of N for rice. The use of Azolla as green manure, and composting of Azolla in rice fields were reported in China, Thailand, Vietnam, Cambodia, Burma, Japan, India and Pakistan.
In the past two decades field experiments have been carried out using rice crop in Research Institutes at Tandojam and Dokri in Sindh, Faisalabd and Kala Shah Kaku in Punjab successfully. It has been observed that mixing Azolla in rice field has increased the production of rice grains when compared with field with Azlla. The fern Azolla under the most favorable condition can fix 7.8-9.7 mg N/g dry weight/day. Azolla releases about 12-20 per cent of its fixed N as ammonia into the surrounding medium. Estimates of total nitrogen inputs of Azolla in paddy soils are rather variable. Estimations of 100-160 kg N/ha/4 months and 500 kg N/ha/year were recorded. Azolla is grown in small plots or ponds as a mono-crop. It is then transferred to the rice field and incorporated into the paddy soil as a green manure before rice transplanting. Azolla is grown as an intercrop with rice by spreading Azolla on the surface of water in rice field. After growth, Azolla either incorporated as a green manure or allowed to die naturally without incorporation. Azolla is grown as both mono crop and intercrop. Azolla has high nitrogen content and a favorable C/N ratio, which allows it to decompose rapidly. When incorporated into the soil, Azolla helps to increase soil organic and improves soil chemical and physical properties. Azolla starts to decompose in 5-10 days and begins to release its nitrogen. The rate of decomposition is significantly affected by the variety, stage of maturity and soil environment. Some rice varieties are more responsive to inoculation with Azolla. Legume crops such as green gram, dhancha, mung, pigeon pea, cow pea, chickpea, lentil, ground nut, clover, guar, soybean, berseem and fenugreek are very important in N-fixation. Thus, in view of the increasing cost of chemical fertilizer, the use of bio-fertilizers is very essential in the present day for increasing the agricultural productivity.