| What percentage of the atmosphere is N2? | 78% |
| Nitrogen Cycle Definition | The Nitrogen Cycle describes the process by which N is gained or lost by the soil; absorbed by plants and returned to the soil as organic matter. |
| 2 Forms of N available to plants | Nitrate-N (NO3)-
Ammonium-N (NH4)+
(Ammonium-N is rapidly converted to Nitrate-N via Nitrification.) |
| Nitrification | The process by which Ammonium-N (NH4)+ is rapidly nitrified into Nitrate-N (NO3)- for crop uptake. Nitrification is a bacterial process and takes place at soil temperatures above 4ºC. |
| Denitrification | The process by which Nitrate-N (NO3)- is reduced to Nitrous oxide (N2O) and Nitrogen gas (N2). This normally occurs in warm, anaerobic soils (typically due to compaction and water-logging). |
| Volatilisation | The process by which Ammonia gas (NH3) is lost from the soil when the concentration of Ammonium-N (NH4)+ exceeds the adsorptive capacity of the soil. |
| Conditions of volatilisation | Light, warm, drying alkaline soils are prone to volatilisation. Most ammonia emissions come from livestock manures during storage and spreading, and some come from the application of urea fertiliser. |
| How to minimise Nitrous Oxide (N2O) emissions | Match N inputs to crop requirements. |
| Soil Nitrogen Supply (SNS) definition | The amount of nitrogen (kg/ha N) in the soil that becomes available for uptake by the crop from establishment to the end of the growing season, taking into account nitrogen losses. |
| SNS Equation | SNS = SMN + estimate of total crop N + estimate of mineralisable N |
| What percentage of the atmosphere is N2? | 78% |
| Leaching | The loss of Nitrate-N (NO3)- via water. |
| Fixation | The process by which atmospheric Nitrogen gas (N2) is converted to organic-N (R-NH2). This is primarily achieved either by rhizobial bacteria in legume nodules or by industrial fertiliser production. |
| Mineralisation | The process by which microbes convert Organic-N (R-NH2) to Ammonium-N (NH4)+. This occurs in warm, moist, well-aerated soils. |
| Immobilisation | The process by which soil organisms consume Nitrate-N (NO3)- or Ammonium-N (NH4)+, converting it to Organic-N (R-NH2), locking it up within their cells until they die and decompose. |
