Answer: Above 10 mmol per kg dry mass.
- A Above 10 mmol per kg dry mass
- B Below 1 mmol per kg mass
- C Exactly 100 mmol per kg
- D Zero for all nutrients
Correct answer: A. Above 10 mmol per kg dry mass
Explanation: By convention a macronutrient is present above about 10 mmol per kg of dry matter; micronutrients occur below that level.
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.