Answer: Living microorganisms that enhance soil nutrient availability: Rhizobium, Azospirillum, mycorrhizal fungi, cyanobacteria.
- A Chemically synthesized fertilizers that have been specially approved for use in certified organic farming systems
- B Living microorganisms that enhance soil nutrient availability: Rhizobium, Azospirillum, mycorrhizal fungi, cyanobacteria
- C Decomposed animal waste material that is applied directly as a bulk soil amendment each season
- D Chemical fertilizers specifically engineered for slow, gradual release of nutrients over many weeks
Correct answer: B. Living microorganisms that enhance soil nutrient availability: Rhizobium, Azospirillum, mycorrhizal fungi, cyanobacteria
Explanation: Biofertilizers are preparations of living microorganisms that improve soil nutrient availability: (1) Rhizobium - N<sub>2</sub> fixation in legumes; (2) Azospirillum/Azotobacter - free-living N<sub>2</sub> fixation; (3) Mycorrhizal fungi - P solubilization; (4) Anabaena/Nostoc - N<sub>2</sub> fixation in paddy fields.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.