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%

Which plant-available form of N is most prone to leaching?

Nitrate (NO3) is most prone to leaching.

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.