Soil bacteria play a vital role in the nitrification process, which releases ammonium from organic matter and transforms it into nitrate, which can be used by plants. The bacteria responsible for nitrification exist mostly in the top few centimeters of the soil profile.
The bacteria work as a team. One group of bacteria, called ammonium oxidizing bacteria, convert ammonium (NH4) into nitrite (N02). The second group, called nitrite oxidizing bacteria, convert nitrite into nitrate (N03).
Unlike many other micro-organisms, nitrifying bacteria do not need to break down organic matter to obtain the carbon they need for growth. Like plants, they obtain carbon from the atmosphere. Organic matter is a source of nitrogen for nitrifying bacteria. The nitrogen is present as protein within the plant residues.
Because of this reliance on nitrogen in organic matter, there is a close association between mineralisation of organic matter and nitrification. Therefore, increasing organic matter levels can affect the activity of these bacteria. By adopting agricultural practices that increase soil organic matter levels, it is
possible to make the use of nitrogen fertilizer more efficient.