I have already reiterated above that nitrogen is necessary for the decomposition of organic matter by heterotrophic microorganisms in the soil. If the organic material being decomposed has a small amount of nitrogen relative to the carbon present (wheat straw, mature cereal stalks).
▶ The microorganisms use some NH4+ or NO3- present in the soil after decomposition. This nitrogen is necessary to allow the rapid growth of the microbial population that accompanies the addition of a large proportion of carbonaceous material to the soil.
▶ Credits: Cimmyt. – [Image of Public Domain]
≕ I invite you to stay tuned and read my next contribution ≔
If, on the other hand, the added material contains a lot of nitrogen in proportion to the carbon present (alfalfa or clover) there will not normally be a decrease in the level of mineral nitrogen in the soil.
In fact, there may be a frankly rapid increase in this fraction of soil nitrogen, caused by its release from the decomposing organic materials.
The ratio of the percentage of carbon to nitrogen is called the carbon: nitrogen ratio, or simply C/N ratio, which defines the relative amounts of these two elements in the recent organic materials, humus, or in the soil as a whole. The C/N ratio of stable soil organic matter is approximately 10:1.
As a general rule, when organic materials with a C/N ratio greater than 30 are added to soils, nitrogen is immobilized during the initial decomposition process. For ratios between 20 and 30, there may be neither immobilization nor release of mineral nitrogen. If organic materials have a C/N ratio of less than 20, mineral nitrogen is released early in the decomposition process.
NOTE: Reference material.