Question

Short/Long Answer type Questions-
a. What are Biofertilizers? What are their main sources? What is biological nitrogen fixation?
b. Name two organisms each which fix nitrogen asymbiotically or symbiotically.

Answer 1

Fertilizers enhance plant growth by providing it with necessary nutrition which primarily includes nitrogen and phosphorus. They are of two types - chemical fertilizers and biofertilizers. The former reduces soil health and causes eutrophication due to water pollution. Therefore, in the current era biofertilizers and biomanures are used more frequently in agricultural settings.

Complete solution:
We will solve this question in parts:
Part a: Biological fertilizers are substances that contain living or dormant microbial cells. When biological fertilizers are applied to their seeds, plant surfaces or soil and colonize the rhizosphere of plants, they increase the nutrient content available for the plant.
Biofertilizers provide nitrogen and phosphorus to the soil.
Microbial cultures of phosphate solubilizing and nitrogen fixing bacteria are used a s biofertilizers. Organic fertilizer is more beneficial than chemical fertilizer.
The main sources of biofertilizers are cow dung, vermicomposts, sludge as they contain many bacteria, fungi and cyanobacteria etc.
Biological nitrogen fixation is the process by which nitrogen fixing microbes called diazotrophs convert dinitrogen to ammonium ions which are then assimilated by plants.
Biological nitrogen fixation is carried out by microorganisms either by symbiotic association or asymbiotically.
Part b: Some examples of biological nitrogen fixers:
Symbiotic diazotrophs - Rhizobium with legumes, Frankia with Alnus etc.
Non-symbiotic/ asymbiotic diazotrophs - Nostoc , Anabaena , Azotobacter etc.

Note:
Several microorganisms are commonly used as organic fertilizers, including nitrogen-fixing soil bacteria (Azotobacter , Rhizobium), nitrogen-fixing cyanobacteria (Anabaena), and phosphorus solubilizing bacteria (Pseudomonas sp). The beneficial interaction of plants and the microbiome represents a promising sustainable solution to improve agricultural production rather than chemical fertilization.