gen-define-the-nitrogen-cycle-in-soil-and-give-one-short-worked-b40a

Define the nitrogen cycle in soil and give one short worked example.

# The Nitrogen Cycle in Soil The nitrogen cycle is the process by which nitrogen is converted between different chemical forms in soil and the environment, making it available for plant uptake. ## Key Processes: 1. **Nitrogen Fixation**: Atmospheric N₂ converted to ammonia (NH₃) by bacteria 2. **Ammonification**: Decomposition of organic matter releases NH₃/NH₄⁺ 3. **Nitrification**: NH₄⁺ → NO₂⁻ → NO₃⁻ (by nitrifying bacteria) 4. **Assimilation**: Plants absorb NO₃⁻ and NH₄⁺ 5. **Denitrification**: NO₃⁻ converted back to N₂ gas (lost to atmosphere) --- ## Worked Example: **Scenario**: A farmer plants legumes (beans) in nitrogen-depleted soil. **Process**: - Rhizobium bacteria in root nodules fix atmospheric N₂ - Production: ~100 kg N/hectare/year as NH₃ - Soil bacteria convert NH₃ → NH₄⁺ → NO₃⁻ - Bean plants absorb NO₃⁻ for protein synthesis - After harvest, crop residues decompose (ammonification) - Released nitrogen enriches soil for next crop **Result**: Soil nitrogen content increases from ~20 kg N/ha to ~120 kg N/ha, reducing need for synthetic fertilizers.