Biofertilizer for Sustainable Agriculture

Biofertilizer refer to as the use of living microorganisms to provide primary nutrients and increase the growth of plants. 

The microorganisms may inhabit in the rhizosphere or inner or surface plant tissues. In here, biochemical reactions of microorganisms are supported in the agriculture to increase the yield. They improve the nutrients availability to the plants. Due to the negative consequences of chemical fertilizers, the farmers tend to use biofertilizers for their crop production.

Biofertilizer are divided into three groups as follows:

1)    Phosphorous fertilizers: It is used to optimize the phosphors level in the soil. It does not depend on the crop to be grown.

2)    Nitrogen fertilizers: It is used to optimize nitrogen level in the soil. Since nitrogen requirements vary with the soil type, types of nitrogen fertilizer depend on the type of nitrogen fertilizers.

3)    Organic fertilizers: the biodegradable organics including animal and plant waste is degraded by aerobic respiratory microorganisms.

The types of biofertilizers are discussed below.

Nitrogen fixers: Nitrogen is considered as a primary nutrient for plant. Even though the nitrogen accounts for 78% of atmosphere gas content, plant cannot absorb directly nitrogen from the atmosphere.  Nitrogen is released into soil trough decomposition of organic matter. Some microorganisms present in the soil are also able to fix atmospheric nitrogen. 

1)    Free living bacteria: they inhabit in the soil. They do not form mutual beneficial symbiotic relationship with plants roots.  Bacteria with different oxygen requirements are available to fix nitrogen.

a.     Ex: Aerobic: Azotobacter

                                                                                      i.      Anaerobic: Clostridium polymyxa

2)    Symbiotic fixers: They from mutual beneficial symbiotic relationship with roots of legumes. The plant tissues make nodules where the symbiotic bacteria inhabit. They fix atmospheric nitrogen into ammonia. The ammonia is available when plant roots die or legume plants are buried directly as the cover crop.

a.     Ex: Rhizobium

3)    Symbiotic cyanobacteria: Cyanobacteria are one of the photosynthetic organisms. Some of them are able to fix atmospheric nitrogen. They form symbiotic relationship with roots of plant including Cycads, liverworts and Azolla. In addition to nitrogen, they add organic matter to the soil through their photosynthesis.

Ex: Anabaena and Nostoc

         But among them Azolla- Anabaena relationship fixes more nitrogen compare to the legume plants so aquatic environments like rice fields use Azolla- Anabaena to increase the yield.

Phosphorous solubilizing bacteria: Phosphorous is also essential nutrient for plant. Phosphorous availability for plant determines solubility and concentration of Phosphorous ions. It is in insoluble forms which is unable to absorb into plants. Inorganic Phosphorous is added to soil by weathering of parent rock. Organic Phosphorous is added to the soil by decomposition of organic matter. The Phosphorous solubilizing bacteria convert the insoluble Phosphorous into soluble Phosphorous which can be absorbed by plants.

Ex: Clostridium polymyxa, Bacillus, Enterobactor

Mycorrhizae: Some fungi found in the soul form mutual beneficial symbiotic relationship with roots of higher plants. The formation of Mycorrhizae is an infection to the plants. Fungi spores germinate near the vicinity of the root zone. Fungal hyphae penetrate and develop into the cortex of the roots. They show filamentous growth on the root surface. The fungal hyphae from arbuscule which is finely divided hyphae. It acts as the nutrients exchange interface between plant and fungal hyphae.  Those fungi association help plants to absorb nutrients in large area while plant provides organic food for them. It helps to correct the phosphors level of plants. It absorbs phosphors from large area and makes them soluble for the plant absorption. In addition to phosphorous uptake, Mycorrhizae secrete growth hormones for plants which are able to accelerate the growth. They promote the symbiotic nitrogen associations.

·        Use of Biofertilizer is more advantageous over chemical fertilizers as follows.

1)    Biofertilizer are required in small quantity: small sized Inoculum of microorganisms is used to inoculate the seeds or plants surfaces. As the living microorganisms are used as the Biofertilizer, small number of microorganism can reproduce and form large colonies.

2)    Increase yield: They are able to increase yield 15-30% by providing essential nutrients. Nutrients availability directly affects the yield. The increasing of yield also varies with type of biofertilizers because capability of different microorganism differs in the nutrients.

3)    Reduce pollution: The farmers tend to add chemical fertilizers in large quantities as they intend increase yield through increasing nutrients availability. But plants absorb nutrients till certain extent. Excess nutrients remain in the soil. They are washed away by runoff. It causes eutrophication in aquatic bodies. But biofertilizers such as Mycorrhizae are capable of absorbing phosphorus in large area so no need of excess chemical fertilizers to be added.

4)    Improve soil structure: fungal hyphae help to bind small soil particles together into large aggregates. Thereby it increases the soil porosity. So water can more easily drained thorough the soil. It also increases the water holding capacity of the soil.