ctsm5.4.036

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Tag name: ctsm5.4.036
Originator(s): slevis, rgknox (Samuel Levis,UCAR/TSS,303-665-1310; Ryan Knox,LBNL,rgk...@lbl.gov)
Date: Mon Apr 27 03:07:00 PM MDT 2026
One-line Summary: Complete the FATES-CLM nitrogen coupling

Purpose and description of changes
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Intoduce code, namelist option, and tests on the CLM side to accommodate interactive nitrogen with FATES.

The FATES side PR is https://github.com/NGEET/fates/pull/1472.

Supporting information (other than in the issue referenced below):
- Nutrient enabled FATES handbook: https://docs.google.com/document/d/1I35fGDfKTkn9_8Z6qXot7HZf3ICSpLONd-iFEErAh0k/edit?usp=drive_link
- FATES CLM N coupling: https://docs.google.com/document/d/1mpBtpCLGJpAGw6R3-nGGY92IWRU3ISvaAUKxvcDVJRw/edit?usp=drive_link

Bugs fixed
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List of CTSM issues fixed (include CTSM Issue # and description) [one per line]:
Resolves #3378

Notes of particular relevance for users
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Changes to CTSM's user interface (e.g., new/renamed XML or namelist variables):
Chaged namelist variable fates_parteh_mode from integer flag to string with options "carbon_only" and "carbon_nitrogen".

Changes made to namelist defaults (e.g., changed parameter values):
Namelist variable suplnitro previously defaulted to NONE for use_cn and to ALL for use_fates. Now it defaults to NONE in all cases except fates_parteh_mode="carbon_only".

Notes of particular relevance for developers:
---------------------------------------------
Changes to tests or testing:
In build-namelist_test.pl, replaced useFATESWOsuplnitro (test in list of tests that are supposed to fail) with useFATESCwsuplnNONE and useFATESCNwuse_fates_sp.
Updated FatesColdPRT2 testmods to use prescribed_p paramfile instead of prescribed_np, because this test runs with interactive nitrogen.
Added testmods FatesColdPRT2_suplnAll (returns the PRT2 test to carbon_only) and FatesColdPRT2_synthN (runs carbon_nitrogen but uses presecribed_np paramfile).
Remove passing test ERP_Ld9.f45_f45_mg37.I2000Clm50FatesCruRsGs.derecho_intel.clm-FatesColdAllVars from expected fails.
Remove machine lawrencium from test-suites as not used and not planned to be used.

Testing summary:
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[PASS means all tests PASS; OK means tests PASS other than expected fails.]

build-namelist tests (if CLMBuildNamelist.pm has changed):

derecho - OK (2 expected failures)

regular tests (aux_clm: https://github.com/ESCOMP/CTSM/wiki/System-Testing-Guide#pre-merge-system-testing):

derecho ----- OK
izumi ------- OK

fates tests comapared to baseline fates-sci.1.92.4_api.45.0.0-ctsm5.4.036 (generated before merging the FATES side PR https://github.com/NGEET/fates/pull/1472):
derecho ----- OK
izumi ------- OK

Answer changes
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Changes answers relative to baseline: Yes

Summarize any changes to answers, i.e.,
- what code configurations: Most, though not Sp and FatesSp
- what platforms/compilers: All
- nature of change: roundoff

In summary, a necessary update in order of operations in CNNDynamicsMod.F90, changes the outcome from b4b to roundoff. A post in the PR (https://github.com/ESCOMP/CTSM/pull/3409#issuecomment-4238969834) explains how I confirmed the transition from b4b to roundoff diffs.

Other details
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List any git submodules updated (cime, rtm, mosart, cism, fates, etc.):
fates from sci.1.92.1_api.44.1.0 to sci.1.92.4_api.45.0.0

Pull Requests that document the changes (include PR ids):
https://github.com/ESCOMP/ctsm/pull/3409

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