C
CraftExam
high importancemedium8 min

Microbes as Biofertilisers

Biofertilisers are microorganisms that enrich soil nutrients or improve nutrient availability to plants through processes such as nitrogen fixation, phosphate absorption and symbiotic association.

Concept Practice Coming Soon

Learn the concept

Student-friendly explanation

Microbial biofertilisers improve soil fertility by natural biological mechanisms. Rhizobium forms nodules in roots of leguminous plants and fixes atmospheric nitrogen into forms usable by plants. Free-living bacteria such as Azotobacter and Azospirillum also contribute to nitrogen enrichment. Cyanobacteria like Anabaena and Nostoc are important in paddy fields because they add organic matter and fix nitrogen. Mycorrhiza is a fungal association with roots that improves absorption of phosphorus and water and can increase plant tolerance under stressful soil conditions. Exams test microbe-crop association, nutrient improved and ecological advantage.

How to write this in exams

  1. 1

    Start with the exact idea

    Biofertilisers are microorganisms that enrich soil nutrients or improve nutrient availability to plants through processes such as nitrogen fixation, phosphate absorption and symbiotic association.

  2. 2

    Then show how to use it

    Name the microbial group. State whether it is symbiotic or free-living. Mention the nutrient or absorption benefit. Give a crop or plant association. Add the ecological advantage if the question asks for importance.

  3. 3

    Add one concrete example

    Rhizobium in root nodules of pea or other legumes fixes atmospheric nitrogen. Anabaena in association with Azolla is a commonly cited example linked with nitrogen enrichment in rice fields.

  4. 4

    Avoid this incomplete answer

    Mycorrhiza fixes atmospheric nitrogen in legume root nodules.

Definition

Biofertilisers are microorganisms that enrich soil nutrients or improve nutrient availability to plants through processes such as nitrogen fixation, phosphate absorption and symbiotic association.

Example

Rhizobium in root nodules of pea or other legumes fixes atmospheric nitrogen. Anabaena in association with Azolla is a commonly cited example linked with nitrogen enrichment in rice fields.

Rule to remember

Key biological rule: biofertilisers increase nutrient availability through living microbial activity, especially nitrogen fixation and improved mineral absorption.

Memory hook

Rhizobium gives nitrogen to legumes; mycorrhiza helps roots absorb minerals and water.

Examples and method

Worked example

Question: Name two biofertilisers and their roles. Answer: Rhizobium fixes atmospheric nitrogen in legume root nodules, while mycorrhiza improves phosphorus and water absorption by plant roots.

Method to apply

Name the microbial group. State whether it is symbiotic or free-living. Mention the nutrient or absorption benefit. Give a crop or plant association. Add the ecological advantage if the question asks for importance.

Diagram support

No compulsory diagram is required, but a root nodule or mycorrhizal root sketch can show the structure-function relation between microbe and plant root.

How CBSE asks it

Asked as organism-role matching, advantages over chemical fertilisers, short notes on cyanobacteria in paddy fields, or assertion-reason on symbiosis.

Avoid common mistakes

Common confusion

Students often write that biofertilisers directly act like chemical fertilisers. Biofertilisers are living organisms that improve nutrient availability through biological activity.

Common wrong answer

Mycorrhiza fixes atmospheric nitrogen in legume root nodules.

Exam tip

Always connect the biofertiliser with the nutrient benefit: Rhizobium for nitrogen in legumes, cyanobacteria for nitrogen in paddy fields, and mycorrhiza for phosphorus absorption.

Quick check

How does mycorrhiza help plants?

Mycorrhiza helps plants because the fungal partner increases the root's absorbing surface and improves uptake of phosphorus and water. In return, the fungus receives food from the plant.

Answer writing and exam use

1-mark answer

Define biofertiliser, give named examples, state the plant association and nutrient role, then add that these microbes help maintain soil fertility through biological processes.

2-mark answer

Define biofertiliser, give named examples, state the plant association and nutrient role, then add that these microbes help maintain soil fertility through biological processes.

3-mark answer

Define biofertiliser, give named examples, state the plant association and nutrient role, then add that these microbes help maintain soil fertility through biological processes.
Practice

Concept practice is coming soon

Join the waitlist for concept-level MCQs and weak-concept practice.

10 MCQs5 MinutesInstant Results
Join Waitlist for Practice

Help improve this page

Found something confusing, incorrect, or missing?

Open Learning Map