User:Hannahbanka26/Agricultural microbiology

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Agricultural microbiology is a branch of microbiology dealing with plant-associated microbes and plant and animal diseases. It also deals with the microbiology of soil fertility, such as microbial degradation of organic matter and soil nutrient transformations.

Fertilizers

Fertilizers are substances used in soil to produce and improve growth in the development of plants. They contain organic and artificial chemicals that are released into the soil and crops to sustain an environment or expel lost chemicals.

Biofertilizers

Biofertilizers are fertilizers that contain living microbes that increase the availability of nutrients by colonizing the rhizosphere or interior of the plant. Biofertilizers are seen as promising, sustainable alternatives to harmful chemical fertilizers due to their ability to increase yield and soil fertility through enhancing crop immunity and development. When applied to the soil, plant, or seed these biofertilizers colonize the rhizosphere or interior of the plant root. Once the microbial community is established, these microorganisms can help to solubilize and break down essential nutrients in the environment which would otherwise be unavailable or difficult for the crop to incorporate into biomass.

Most common biofertilizers contain Rhizobium, Azotobacter, Azospirilium, and blue-green algae (BGA). Rhizobium forms a symbiotic relationship with leguminous plants through its root nodule and Azotobacter is used in wheat, cotton and potato. Azophirlium is used for sugarcane and millet. Nitrogen fixation is required for crops in wetlands and ponds which is completed by BGA.

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Bio fertiilizers

biofertilizers are characterized as two systems based on how the preparation of biofertilizers as either solid carrier-based system or liquid-carrier based. Most biofertilizers contain rhizobium as the bacteria as they have a symbiotic relationship with the roots. The inoculation process is done through nodule formation with the bacterial strain population and the root of the plant. To ensure the longevity of the inoculated bacteria to stay on the carrier it is sterilized using either Gamma-irradiation or an autoclave. The Gamma irradiation process allows the bacteria and carrier to stay in their original state but adds a coating of a thin polythene bag. The autoclave process covers a carrier with a polypropylene bag that is left partially open at 121 degrees Celsius for an hour.

The solid carrier based is a technique that can be dated back to the ancient era but has developed and been modified throughout the years to adapt to various microbes and solid carriers. The liquid carrier-based bio fertilizer is similar to the solid system process with the exception of it being a liquid form. It is predominately used for the formation of resting spores and cysts allowing for it to develop a tolerance to adverse conditions as well as increasing its shelf life. The process of the attachment of the liquid bio fertilizer is dependent on the presence of carbon within the soil which allows for germination and activation of dormant cells.

Recent studies suggest that the benefits of using liquid biofertilizers as an alternative to synthetic fertilizers might be the most efficient and sustainable agriculture system as it has a longer shelf life, the ability to retain moisture and a higher survival rate of seed and nodulation. Comparatively the solid carrier system has a higher risk of contamination, is more sensitive to high temperatures and requires 10 times the amount of liquid bio fertilizer.

Liquid biofertilizers are categorized based off the chemical components such a nitrogen fixing, phosphate solubilizing, potassium mobilizing and specifically for micronutrients.

Soil microorganisms[edit]

Importance of soil microorganisms

• Involved in nutrient transformation process
• Decomposition of resistant components of plant and animal tissue
• Role in microbial antagonism

Microorganisms as biofertilizers

Nitrogen

Nitrogen is an essential element needed for the creation of biomass and is usually seen as a limiting nutrient in agricultural systems. Though abundant in the atmosphere, the atmospheric form of nitrogen cannot be utilized by plants and must be transformed into a form that can be taken up directly by the plants; this problem is solved by biological nitrogen fixers. Nitrogen fixing bacteria, also known as diazotrophs, can be broken down into three groups: free-living (ex. Azotobacter, Anabaena, and Clostridium) , symbiotic (ex. Rhizobium and Trichodesmium) and associative symbiotic (ex. Azospirillum). These organisms have the ability to fix atmospheric nitrogen to bioavailable forms that can be taken up by plants and incorporated into biomass. An important nitrogen fixing symbiosis is that between Rhizobium and leguminous plants. Rhizobium have been shown to contribute upwards of 300 kg N/ha/year in different leguminous plants, and their application to agricultural crops has been shown to increase crop height, seed germination, and nitrogen content within the plant. The utilization of nitrogen fixing bacteria in agriculture could help reduce the reliance on man-made nitrogen fertilizers that are synthesized via the Haber-Bosch process.

Phosphorus

Phosphorus can be made available to plants via solubilization or mobilization by bacteria or fungi. Under most soil conditions, phosphorus is the least mobile nutrient in the environment and therefore must be converted to solubilized forms in order to be available for plant uptake. Phosphate solubilization is the process by which organic acids are secreted into the environment, this lowers the pH and dissolves phosphate bonds therefore leaving the phosphate solubilized. Phosphate-solubilizing bacteria (PBS) (ex. Bacillus subtilis and Bacillus circulans) are responsible for upwards of 50% of microbial phosphate solubilization. In addition to the solubilized phosphate, PBS can also provide trace elements such as iron and zinc which further enhance plant growth. Fungi (ex. Aspergillus awamori and Penicillium spp.) also perform this process, however their contribution is less than 1% of all activity. A 2019 study showed that when crops were inoculated with Aspergillus niger , there was a significant increase fruit size and yield compared with non-inoculated crops; when the crop was co-inoculated with A. niger and the nitrogen fixing bacteria Azobacter, the crop performance was better than with inoculation using only one of the biofertilizer and the crops that were not inoculated at all. Phosphorus mobilization is the process of transferring phosphorus to the root from the soil; this process is carried out via mycorrhiza (ex. Arbuscular mycorrhiza) . Arbuscular mycorrhiza mobilize phosphate by penetrating and increasing the surface area of the roots which helps to mobilize phosphorus into the plant. Phosphate solubilizing and mobilizing microorganisms can contribute upwards of 30–50 kg P2O5/ha which, in turn, has the potential to increase crop yield by 10–20%.

Applications

• DAP
• UREA
• SUPER PHOSPHATE

DAP

DAP known as ammonium phosphate is a fertilizer that contains 18% nitrogen, 46% phosphorus and 18 primary plant nutrients. The ammonium reacts with the phosphorus under controlled conditions with the fertilizer plants.

UREA

Urea is a fertilizer that is used mostly where nitrogen is required in for plant fertility. It is usually found in the anhydrous ammonia that contains 46% urea. It works by converting into ammonium bicarbonate and released into into air as ammonia gas. For urea to work efficiently it needs to be directed into the soil rather than it's surface. This is done by injecting or banding it into the soil. It is a popular fertilizer due to it being low cost and easy storage and handling.

Super Phosphate

Super phosphate is known as the first ever chemical fertilizer that was made by bonemeal and sulphuric acid. It then became super phosphate when sulphuric acid was used to treat a rock ore phosphate. It is used to improve a plants metabolism, quantity and quality of crops.

References

1. Gibbons, N. E. (1963). Recent progress in microbiology: symposia held at the VIII International Congress for Microbiology, Montreal, 1962. University of Toronto Press.
2. de Mendonça, H.V., Martins, C.E., da Rocha, W.S.D. et al. Biofertilizer Replace Urea as a Source of Nitrogen for Sugarcane Production. Water Air Soil Pollut 229, 216 (2018). https://doi.org/10.1007/s11270-018-3874-2
3. Mahanty, T., Bhattacharjee, S., Goswami, M., Bhattacharyya, P., Das, B., Ghosh, A., & Tribedi, P. (2017). Biofertilizers: A potential approach for sustainable agriculture development. Environmental Science and Pollution Research, 24(4), 3315-3335. doi:https://doi.org/10.1007/s11356-016-8104-0
4. Mishra, B. B. (2021). Environmental and agricultural microbiology : applications for sustainability (B. B. Mishra, Ed.). John Wiley & Sons.
5. Allen V. Barker, in Encyclopedia of Analytical Science (Third Edition), 2019
6. Urea. Agrico . (n.d.). Retrieved March 30, 2023, from https://www.agricocanada.com/fertilizers/urea/