Everything you need to know about bio-fertilizers. Some of the most frequently asked exam questions are as follows:-
Q.1. What are the substitutes of calcium carbonate for pelleting?
Ans: The substances used for pelleting other than lime are gypsum, bentonite, rock phosphate and charcoal.
Q.2. How much nitrogen may be fixed in Rhizobium legume association?
Ans: 50 to 100 kg N/hectare.
Q.3. What may be the reasons for poor or no response of the inoculation with Rhizobium?
Ans: The reasons for poor or no response of the inoculation with Rhizobium are:
(1) Failure of germination of seeds due to poor quality of seeds and lack of moisture.
(2) Failure of seedlings to produce nodules due to poor quality of inoculants, adverse soil conditions, use of wrong rhizobia and incompatibility of pesticides.
(3) Ineffective nodulation due to competition created by native population of rhizobia, thereby causing failure of newly introduced legume crops.
(4) Nutritional deficiencies of demerits such as phosphorus, calcium and molybdenum needed in protein synthesis and Cell wall development of plants and required by the rhizobia.
(5) Due to competition with other plants for moisture, nutrients and space.
Q.4. List the number of species of Azotobacter differentiated on the basis of morphological and physiological features.
Ans: According to ‘Bergey’s Manual of Determinative Bacteriology’ 9th edition (1994) on the basis of motility, water soluble pigments formed for utilization of carbon source by the Azotobacter there are 6 species in this genus. They are A. armeniacus, A. beijerinckii, A. chroococcum, A. Nigerians, A. paspali and A. vinelandii.
Q.5. Which are the species of Azotobacter that occur commonly in India?
Ans: A. beijerinckii and A. vinelandii are common in India.
Q.6. Which species of Azotobacter occurs in acid soils?
Ans: A. chroococcum occurs in acidic soils.
Q.7. Name the species of Azotobacter that occurs in neutral and alkaline soils.
Ans: A. beijerinckii.
Q.8. Which is the suitable medium for Azotobacter?
Ans: Nitrogen free agar medium, e.g., Ashby’s medium.
Q.9. What are the characteristics of the colonies of Azotobacter after incubation at 30°C for 3-4 days?
Ans: Soft, milky and mucoid colonies.
Q.10. Who was the first to record that Azospirillum lipoferum (old name, Spirillum lipoferum) fixes up atmospheric nitrogen?
Ans: Beijerinck in 1925.
Q.11. Which species of Azospirillum is generally found associated with the roots of C4-plants?
Ans: A. lipoferum.
Q.12. Which species of Azospirillum is generally found associated with the roots of C3-plants in tropical and subtropical regions?
Ans: A. brasilense.
Q.13. Which is the suitable medium for the cultivation of Azospirillum?
Ans: Semisolid nitrogen free sodium malate medium.
Q.14. What is the systematic position of Azospirillum?
Ans: The genus Azospirillum belongs to Group 2 of Aerobic/Microaerophilic, Motile, Helical/Vibroid Gram-negative Bacteria in 9th edition (1994) of ‘Bergey’s Manual of Determinative Bacteriology’.
Q.15. What is the characteristic of the growth of Azospirillum while incubated at 35°C for 48 hours?
Ans: Formation of white pellicle 2-4 mm, below the surface of the medium.
Q.16. Name the species of Azospirillum.
Ans: According to 9th edition (1994) of ‘Bergey’s Manual of Determinative Bacteriology’ there are five species in the genus Azospirillum. They are Azospirillum amazonense, A. brasilense, A. halopraeferens, A. irakense, and A. lipoferuni.
Q.17. Which are the major genera with maximum number of nitrogen fixing species?
Ans: Anabaena, Aulosira, Cylindrospermum, Nostoc, Plectonema, Scytonema and Tolypothrix.
Q.18. Distribution of nitrogen fixing blue green algae (BGA) varies from 4 to 80 per cent in different soils. Which are the genera ubiquitous in all regions?
Ans: Anabaena and Nostoc.
Q.19. Which is the most common species of Azolla in India?
Ans: Azolla pinnata.
Q.20. Which species of BGA is symbiont of Azollal?
Ans: Anabaena azollae is found in cavities on dorsal leaves.
Q.21. How much nitrogen generally occur in Azollal?
Ans: 0.2 to 0.3% of its fresh weight and 3 to 5% nitrogen of dry weight.
Q.22. What are diazotrophs? Name some of them.
Ans: The procaryotes that can carry on nitrogen fixation are called diazotrophs. They are various cyanobacteria, members of Azotobacteriaceae, e.g., Azotobacter chroococcum, members of Rhizobiaceae, e.g., Rhizobium leguminosarum, some species of Bacillus and Clostridium.