Appendices - Soil Essentials: Managing Your Farm's Primary Asset - page 152

Appendix 8. The nitrogen cycle

Free nitrogen in air

Fertilizer manufacture

Volatilisation
e.g. from urea,
NH 3 and urine

Nitrogen from
air fixed by
rhizobium in
nodules

Animal life

Grass

Legume

Animal excreta

Dead leaves
and roots

Dead leaves
and roots

Decaying organic litter

Soil organic matter
(or humus)

Absorbed by
grass roots

Ammonium
nitrogen

Denitrification

Nitrate nitrogen

Losses by leaching