Nitrification and Ammonification

Nitrification : Nitrification is an exothermic reaction. Most of the soil bacteria participate in converting ammonia into nitrate, the form of nitrogen that can be used by plants and animals. This involves two steps performed by two different types of bacteria. First, soil bacteria such as Nitrosomonas and Nitrosococcus convert ammonia into nitrite:

2NH3 + 3O2 --(Nitrosomonas, Nitrosococcus)--> 2HNO2 + 2H2O

Then another soil bacterium, Nitrobacter, adds a third oxygen atom to create nitrate:

2HNO2 + O2 --(Nitrobacter)--> 2HNO3

These bacteria are chemoautotrophs: by metabolising nitrogen along with oxygen they obtain the energy to power their own life processes.

Symbiotic N2 fixation : The best known nitrogen-fixing symbiotic bacterium is Rhizobium. This soil-dwelling bacterium forms root nodules in plants belonging to the family Fabaceae, e.g. beans, gram and groundnut. …