List and describe the main phases of the nitrogen cycle.

(N/A) The nitrogen cycle is a biogeochemical process by which nitrogen is converted into various chemical forms as it circulates among the atmosphere,terrestrial,and marine ecosystems. The main phases are:
$1$. Nitrogen Fixation: The process of converting atmospheric nitrogen $(N_2)$ into ammonia $(NH_3)$ or other nitrogenous compounds. This can occur through biological fixation (by microbes like $Rhizobium$,$Azotobacter$),industrial fixation,or atmospheric fixation (lightning).
$2$. Nitrification: The process where ammonia is oxidized to nitrite $(NO_2^-)$ by bacteria like $Nitrosomonas$ and $Nitrococcus$,and then further oxidized to nitrate $(NO_3^-)$ by $Nitrobacter$.
$3$. Assimilation: Plants absorb nitrate or ammonia from the soil and incorporate them into organic molecules like amino acids and proteins.
$4$. Ammonification: The decomposition of organic nitrogenous compounds (from dead plants and animals) back into ammonia by decomposers like bacteria and fungi.
$5$. Denitrification: The process where nitrate in the soil is reduced back to gaseous nitrogen $(N_2)$ by denitrifying bacteria such as $Pseudomonas$ and $Thiobacillus$,returning it to the atmosphere.