This process of nitrification involves two groups of soil bacteria. Mineralization is the process of converting organic N to plant-available inorganic forms. It is a gradual breaking down of large molecules to smaller molecules by soil microorganisms. After these microbes complete their relatively brief life cycles, they are decomposed by other microbes. Energy for this process comes from carbon in the material being used, so introduction of fresh plant materials stimulates breakdown activity.
Immobilization occurs when plants and soil microorganisms incorporate inorganic into organic form.
Because it depends largely on microbes, the availability of carbon and other nutrients determines the rate of immobilization. This effect eventually fades because, without external N, the microbial population dies and decomposes, releasing N that is available to plants. The risk of immobilization is avoided by mixing plant residue into the soil well before the next cropping cycle. Loss of Nitrogen from Soils Even though soil N may be unavailable to plants through immobilization, it has not disappeared from the soil. Nitrogen can be permanently removed from soil by erosion, leaching, denitrification, or volatilization.