During decomposition, when is immobilization of inorganic nitrogen most likely to occur?

Immobilization of inorganic nitrogen occurs when soil microorganisms consume inorganic nitrogen to build their own biomass during the decomposition of organic materials. This process is influenced significantly by the carbon-to-nitrogen (C:N) ratio of the decomposing material.

When the C:N ratio is around 35, it is often considered the threshold for achieving a balanced nutrient supply for microorganisms. At this ratio, nitrogen is readily available, allowing microbes to effectively utilize both carbon and nitrogen. This leads to the process of immobilization, where inorganic nitrogen is incorporated into microbial biomass as they decompose the organic matter, effectively reducing the amount of available inorganic nitrogen in the soil.

In contrast, when the C:N ratio is significantly higher, such as 50 or 100, it indicates that there is a surplus of carbon relative to nitrogen. In these situations, microorganisms often struggle to find sufficient nitrogen, leading to mineralization of organic nitrogen (rather than immobilization) as they try to balance their nutrient intake. A C:N ratio of 15 may also facilitate decomposition without significant immobilization because the carbon is consumed rapidly, often resulting in little competition among microbes for nitrogen.

Thus, the selection of a C:N ratio around 35 aligns with the most likely conditions for immobil