## 2.22.1. Summary of CLM5.0 updates relative to CLM4.5[¶](#summary-of-clm5-0-updates-relative-to-clm4-5 "Permalink to this headline")
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We describe external inputs to the nitrogen cycle in CLM5.0.  Much of the following information appeared in the CLM4.5 Technical Note ([Oleson et al. 2013](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#olesonetal2013)) as well as [Koven et al. (2013)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#kovenetal2013).

CLM5.0 includes the following changes to terrestrial nitrogen inputs:

*   Time varrying deposition of reactive nitrogen. In off-line runs this changes monthly. In coupled simulations N deposition is passed at the coupling timestep (e.g., half-hourly).
    
*   Asymbiotic (or free living) N fixation is a function of evapotranspiration and is added to the inorganic nitrogen (NH4+) pool (described below).
    
*   Symbiotic N fixation is handled by the FUN model (chapter [2.18](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/FUN/CLM50_Tech_Note_FUN.html#rst-fun)) and is passed straight to the plant, not the mineral nitrogen pool.
    

