The Nitrogen Cycle
Additions to the soil
Nitrogen in the Atmosphere --> Soluble Nitrogen compounds (NH+, NO2-, NO3-)
- this takes place due to biological fixation by bacteria in the soil and root nodules in legumes
- a reducing agent is needed to provide the electrons
- lightining, burning hydrocarbon fuels and natural fires all produce nitrogen oxides
- the nitrogen oxides are deposited on the soil
- ammonium ions are also deposited on the soil, which come from ammonia given out by animal excreta
Animal excreta, crop wastes, silage effluent and sewage all contribute to the organic nitrogen compounds in the soil.
Fertilisers and rain add to the soluble nitrogen compounds in the soil.
Conversions in the soil
Organic nitrogen compounds --> soluble nitrogen compounds (NH4+, NO2-, NO3-)
- this takes place in a process called mineralisation
- it is faster at the higher temperature of tropical soils
Ammonium ions (NH4+) --> Nitrate(III) ions --> Nitrate(V) ions
- this takes place through nitrification of bacteria in the soil (oxidation)