The Nitrogen Cycle in Garden Soil

By James Wilson · October 15, 2026

Overview of the Nitrogen Cycle

Nitrogen is the nutrient plants need in the largest quantity. The nitrogen cycle describes how nitrogen moves between the atmosphere, soil, and living organisms through a series of bacterial transformations.

Key Processes

Nitrogen fixation: Bacteria convert atmospheric N2 into ammonia (NH3)
Nitrification: Ammonia is converted to nitrite, then nitrate by soil bacteria
Mineralization: Organic nitrogen in dead matter is converted to ammonium
Denitrification: Nitrate is converted back to N2 gas under waterlogged conditions

Practical Implications

Nitrate is the form plants absorb most easily, but it leaches quickly through soil. Ammonium sticks to soil particles but must be converted to nitrate first. This is why slow-release fertilizers and organic amendments provide more steady nutrition.

Managing Nitrogen in Gardens

Legume cover crops fix atmospheric nitrogen through symbiotic bacteria in root nodules. Incorporating legumes before planting reduces fertilizer needs. Avoid overwatering, which promotes denitrification and nitrogen loss.

The Nitrogen Cycle in Garden Soil

Overview of the Nitrogen Cycle

Key Processes

Practical Implications

Managing Nitrogen in Gardens

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