Bio-fertilizers for organic farming
GENERALLY, AGRICULTURAL land becomes poor in fertility after long term cultivation, if not supplemented with proper inputs. To supplement the soil nutrient contents under conventional farming system, we need to apply high doses of agrochemicals (i.e. chemical fertilizers).
Although chemical fertilizers increase the crop yields up to a significant level, but their cost has been increasing rapidly. Moreover, they have many negative effects both on environment and human health. The toxic chemicals present in fertilizers are absorbed by plants and enter the food chain through vegetables and cereals. The most harmful effect of fertilizers on human health is the seepage of chemicals into the ground water which is then extracted in drinking water. This water can contain high levels of nitrates and nitrites that cause blue baby syndrome. Mercury, lead, cadmium and uranium are very toxic metals that have been found in fertilizers and can cause problems in kidneys, lungs and liver and can also cause cancer depending upon their quantities consumed by humans.
Therefore, in order to make agriculture sustainable, it is necessary to implement a balanced and responsible use of organic agriculture. The principles of organic farming also outlines the similar concepts where the soil health and biodiversity is built up to sustain the plant growth in longer term.
Biofertilizers such as Rhizobium, Frankia, Azospirillum, Azotobacter and Cyanobacteria play important roles in improving the nutrient supplies. The name itself is self explanatory. Biofertilizer is a ready-to-use live formulation of such beneficial microorganisms which on application to seed, root or soil, mobilize the availability of nutrients by their biological activity. They are eco-friendly, cost effective and renewable source of plant nutrients. They can play a vital role in maintaining long term soil fertility and sustainability. The bio fertilizers are important to ensure a healthy future for the generations.
Among all the biofertilizer, Rhizobium is the maximum researched bio-fertilizer. The nutrients fixed by the soil microbes are more effective than outside application. It has been estimated that nearly 80,000 tonnes of nitrogen is available over an area of one hectare land (as we know that atmospheric air contains 78% nitrogen). The biofertilizers trap some amount of this nitrogen and fix in the soil which benefits the plant. Use of biofertilizers in crop production also improves soil biological properties, besides providing nutrients to the soil.
Classification of Biofertilizers:
A simple form of classification of biofertilizers is given below:
For Nitrogen: Rhizobium for legume crops. Azotobacter, Azospirillum for non legume crops. Acetobacter for sugarcane only. Blue -Green Algae (BGA) and Azolla for low land paddy.
For Phosphorous: Phosphatika for all crops to be applied with Rhizobium, Azotobacter and Acetobacter.
For Enriched Compost: Cellulolytic fungal culture, and phosphotika and Azotobacter culture are used as enriched compost. Apart from these common sources of biofertilizers, some newly identified microorganisms for nitrogen fixation are also in use such as Azorhizobium caulinodans. It is being used successfully in rice and maize. Acetobacter are another new strain of biofertilizer being used in sugarcane. Furthermore, Sinorhizobium can be used for nodulating the soybean crop. Microbes like Thiobacillus thiooxidans are known for sulphur and iron oxidization.
There are many advantages of using the biofertilizers.
• They fix atmospheric nitrogen.
• Increase availability or uptake of nutrients through solubilization or increased absorption.
• Stimulate plant growth through hormonal or antibiotics action or by decomposing organic waste.
• They are cheap, hence, reduce cost of cultivation.
• Improve soil properties and sustaining soil fertility that lead to soil enrichment.
• They are eco-friendly and pose no damage to the environment.
Constraints in Using Biofertilizers: As such there is no harmful impact of biofertilizers if it is used properly but there are some constraints in using biofertilizers:
• They are specific to the plants.
• The acceptability of biofertilizers has been rather low chiefly because they do not produce quick and spectacular responses like chemical fertilizers.
• Require skill in production and application.
• They are difficult to store.
• Inadequate awareness about its use and benefits.
• Lack of availability of quality products in time to the farmers in rural areas.
Consequently, biofertilizers are a vital component for the soil fertility management in sustainable agriculture. Equally they are also suitable for our organic farming. Once they are established, the soil fertility can be maintained over the years. Almost all the essential plant nutrients can be supplied through biofertilizers to the crops. The microorganisms such as rhizobium, azotobactor, azospirillum, azorhizobium, sinorhizobium, acetobacter, frankia, phosphate solublizers, VAM, Azolla- Blue green algae etc., have been used as biofertilizers for many plants under various ecological and geographical systems. They enhance the absorption and make available the nutrients to the plants. These microorganisms may be symbiotic, associated or free living in nature.