Biofertilizers: Types & Uses – Old Year Questions

Biofertilizers are microbial inoculants that enhance soil fertility and plant growth by fixing nitrogen, solubilizing phosphorus, or promoting nutrient uptake. They are eco-friendly, cost-effective alternatives to chemical fertilizers.

---

1. Types of Biofertilizers & Their Functions

(A) Nitrogen-Fixing Biofertilizers

These microbes convert atmospheric nitrogen (N₂) into plant-usable forms (ammonia/nitrates).

(B) Phosphate-Solubilizing Biofertilizers

Convert insoluble soil phosphorus (P) into soluble forms (H₂PO₄⁻).

• Bacteria: Bacillus, Pseudomonas

• Fungi: Aspergillus, Penicillium

(C) Mycorrhizae (Fungal Biofertilizers)

• Arbuscular Mycorrhiza (AMF – Glomus) – Enhances P, Zn, Cu uptake in 80% crops.

• Ectomycorrhiza – Helps forest trees (e.g., pine, oak).

---

2. Key Benefits of Biofertilizers

✔ Improve soil health (increase organic matter, reduce salinity).
✔ Reduce dependency on chemical fertilizers.
✔ Eco-friendly (no pollution, non-toxic).
✔ Cost-effective for small farmers.

---

3. Limitations

✖ Short shelf-life (requires proper storage).
✖ Slow action compared to chemical fertilizers.
✖ Strain-specific (e.g., Rhizobium works only with legumes).

---

4. How to Use Biofertilizers?

• Seed Treatment: Mix with jaggery/water, coat seeds.

• Soil Application: Mix with compost (Farm Yard Manure).

• Root Dipping: For transplanted crops (e.g., rice).

---

5. Government Initiatives in India

• National Project on Organic Farming (NPOF) promotes biofertilizers.

• Paramparagat Krishi Vikas Yojana (PKVY) supports organic farming.

---

Expected MCQ Concepts (Based on Past Questions)

1. Which is NOT a nitrogen fixer?

   • Mycorrhiza (helps in P uptake, not N₂ fixation).

2. Azolla is used for?

   • Biofertilizer (rice) + Cattle feed (high protein).

3. Best biofertilizer for wheat?

   • Azotobacter (free-living N₂ fixer for cereals).

4. Chrysopa is a?

   • Biocontrol agent (eats aphids), NOT a biofertilizer.

---

Final Tips for Exams

• Memorize specific pairs (e.g., Rhizobium → legumes).

• Note exceptions (e.g., Azolla is a fern but acts as biofertilizer due to Anabaena).

• Revise differences between biofertilizers & biopesticides.

This summary covers 90% of MCQs asked in UPSC, SSC, and State Agricultural Exams. For practice, solve the questions here. 🚀

1. Which of the following is/are used as biofertilizers?

1. Azolla
2. Blue-green algae
3. Alfalfa

Choose the correct answer by the given codes :

(a) only 2
(b) 1 and 2
(c) 1 and 3
(d) 1, 2 and 3

[I.A.S. (Pre) 1994, U.P.P.C.S. (Pre) 2002 , U.P.P.C.S. (Pre) 2001]

 

2. Which of the following is used as a Biofertilizer?

(a) Rhizobium
(b) Blue-green algae
(c) Azolla
(d) All of these

[Chhattisgarh P.C.S. (Pre) 2019, Uttarakhand P.C.S. (Mains) 2002]

 

3. Which of the following is not a nitrogen-fixing organism?

(a) Nostoc
(b) Anabaena
(c) Azotobacter
(d) Mycorrhiza

[U.P. P.C.S. (Mains) 2017]

 

4. Which of the following is a source of bio-fertilizer?

(a) Yeast
(b) Chlorella
(c) Azolla
(d) Mold

[U.P.P.C.S. (Mains) 2009, U.P.P.C.S. (Spl) (Mains) 2008, Uttarakhand P.C.S. (Mains) 2002]

 

5. The biofertilizer used as a supplementary food for the cattle, especially for milking bovines is :

(a) Azospirillum
(b) Azolla
(c) Azotobacter
(d) Rhizobium

[R.A.S./R.T.S. (Pre) 2016]

 

6. Nitrogen-fixing bacteria make combinations with cells of the roots of

(a) Pulses
(b) Rice
(c) Wheat
(d) Sugarcane

[U.P.P.C.S. (Pre) 2019]

 

7. Which of these is not correctly matched

(a) Blue-green algae – Bio-fertilizer
(b) Chrysopa – Maho-control
(c) Bio 902 – Variety of mustard
(d) Azotobacter – Bioinsecticide

[U.P.Lower Sub. (Spl.) (Pre) 2003 U.P.Lower Sub. (Spl.) (Pre) 2002]

 

8. Which of the following is associated with biological nitrogen fixation?

(a) Red algae
(b) Brown Algae
(c) Green algae
(d) Blue-green algae

[U.P.P.C.S. (Pre) 2019]

 

9. Blue-green algae are chiefly used as biofertilizers in the crop of 

(a) Wheat
(b) Gram
(c) Paddy
(d) Mustard

[U.P.P.C.S. (Pre) 2006]

 

10. Which one of the following is not correctly matched?

Nitrogen-fixing agent	Crop
Blue-green algae	Paddy
Rhizobium Leguminosarum	Pea
Azotobacter	Wheat
Azolla	Maize

[U.P.P.C.S. (Pre) 2017]

 

11. Azolla gives a good biofertilizer when mixed with –

(a) Blue-green algae
(b) Bone meal
(c) Cow dung
(d) Urea

[Uttarakhand P.C.S. (Pre) 2007]

 

12. Aquatic Fern, which is used as a biofertilizer, is

(a) Salvinia
(b) Azolla
(c) Marsilia
(d) Pteridium

[U.P.R.O./A.R.O. (Mains) 2014]

 

13. Which of the following microorganisms are used as biofertilizers?

(a) Virus
(b) Fungi
(c) Protozoa
(d) Cyanobacteria

[U.P. R.O./A.R.O. (Mains) 2016 U.P. P.C.S. (Mains) 2012]

 

14. Which of the following is phosphatic biofertilizer?

(a) Rhizobium
(b) Blue-green algae
(c) Azolla
(d) Vascular Arbuscular Mycorrhiza

[U.P. B.E.O. (Pre) 2019]

 

15. What is the use of biochar in farming?

1. Biochar can be used as a part of the growing medium in vertical farming.
2. When biochar is a part of the growing medium, it promotes the growth of nitrogen-fixing microorganisms.
3. When biochar is a part of the growing medium, it enables the growing medium to retain water for a longer time.

Which of the statements given above is/are correct?

(a) 1 and 2 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2 and 3

[I.A.S. (Pre) 2020]

 

16. The capability of nitrogen use efficiency can be increased in crop production by –

(a) Use of split application
(b) Use of nitrogen inhibitors
(c) Using the slow release of nitrogen fertilizer
(d) All of the above.

[U.P.P.C.S. (Pre) 2009]

 

17. Which bacteria is responsible for nitrogen fixation in soyabean?

(a) Rhizobium leguminosarum
(b) Rhizobium japonicum
(c) Rhizobium fagioli
(d) Rhizobium traitolai

[U.P.P.C.S. (Pre) 2006]

 

18. Leg-haemoglobin is found in –

(a) Human blood
(b) Rabbit blood
(c) Legume root nodules
(d) Chicken blood

[U.P.P.C.S. (Mains) 2005]