Move nfix_method from a hardwired variable to the namelist

bld/CLMBuildNamelist.pm

@@ -3381,7 +3381,7 @@ sub setup_logic_mineral_nitrogen_dynamics {
   #
   my ($opts, $nl_flags, $definition, $defaults, $nl) = @_;
 
-  my @vars = ( "freelivfix_slope_wet", "freelivfix_intercept" );
+  my @vars = ( "freelivfix_slope_wet", "freelivfix_intercept", "nfix_method" );
   if (  &value_is_true($nl_flags->{'use_cn'}) && &value_is_true($nl->get_value('use_fun')) ) {
     foreach my $var ( @vars ) {
        add_default($opts, $nl_flags->{'inputdata_rootdir'}, $definition, $defaults, $nl, $var,
@@ -3394,6 +3394,12 @@ sub setup_logic_mineral_nitrogen_dynamics {
        }
     }
   }
+
+  my $var = $nl->get_value('nfix_method');
+  if ( $var ne "'Houlton'" && $var ne "'Bytnerowicz'" ) {
+    $log->fatal_error("$var is incorrect entry for the namelist variable nfix_method; expected Houlton or Bytnerowicz");
+  }
+
 }
 
 

bld/namelist_files/namelist_defaults_ctsm.xml

@@ -2024,6 +2024,8 @@ lnd/clm2/surfdata_esmf/NEON/ctsm5.3.0/surfdata_1x1_NEON_TOOL_hist_2000_78pfts_c2
 <freelivfix_intercept use_fun=".true." use_cn=".true.">0.0117d00</freelivfix_intercept>
 <freelivfix_slope_wet use_fun=".true." use_cn=".true.">0.0006d00</freelivfix_slope_wet>
 
+<nfix_method>Houlton</nfix_method>
+
 <br_root>0.83d-06</br_root>
 
 <!-- Scalar of leaf respiration to vcmax (used for SP mode and with luna) (could vary with physics version) -->

bld/namelist_files/namelist_definition_ctsm.xml

@@ -388,6 +388,11 @@ Slope of free living Nitrogen fixation with annual ET
 Intercept of free living Nitrogen fixation with zero annual ET
 </entry>
 
+<entry id="nfix_method" type="char*25" category="clm_nitrogen"
+       group="clm_nitrogen" valid_values="Houlton,Bytnerowicz" value="Houlton" >
+Choice of nfix parameterization
+</entry>
+
 <entry id="use_undercanopy_stability" type="logical" category="clm_physics"
        group="canopyfluxes_inparm" valid_values="" >
 If TRUE use the undercanopy stability term used with CLM4.5 (Sakaguchi&amp;Zeng, 2008)

src/biogeochem/CNFUNMod.F90

@@ -206,7 +206,7 @@ subroutine CNFUN(bounds,num_soilc, filter_soilc,num_soilp&
    use clm_time_manager, only : get_step_size_real, get_curr_date
    use clm_varpar      , only : nlevdecomp
    use clm_varcon      , only : secspday, smallValue, fun_period, tfrz, dzsoi_decomp, spval
-   use clm_varctl      , only : use_nitrif_denitrif
+   use clm_varctl      , only : use_nitrif_denitrif, nfix_method
    use PatchType       , only : patch
    use subgridAveMod   , only : p2c
    use pftconMod       , only : npcropmin
@@ -487,15 +487,14 @@ subroutine CNFUN(bounds,num_soilc, filter_soilc,num_soilp&
   integer   :: icost                             ! a local index
   integer   :: fixer                             ! 0 = non-fixer, 1
   ! =fixer 
-  !TODO, make namelist option
-  integer   :: nfix_method = 2                   ! 1 = Houlton, 2 = Bytnerowicz
   logical   :: unmetDemand                       ! True while there
   !  is still demand for N
   logical   :: local_use_flexibleCN              ! local version of use_flexCN
   integer   :: FIX                               ! for loop. 1 for
   !  fixers, 2 for non fixers. This will become redundant with the
   !   'fixer' parameter if it works. 
 
+  character(len=32) :: subname = 'CNFUN'
   !--------------------------------------------------------------------
   !---------------------------------
   associate(ivt                 => patch%itype                                          , & ! Input:   [integer  (:) ]  p
@@ -1063,19 +1062,19 @@ subroutine CNFUN(bounds,num_soilc, filter_soilc,num_soilp&
                  fixer=0
                endif
 
-               ! TODO, make this a name list change determining which equation to use
-               if (nfix_method == 1) then
-                 ! This calls the Houlton function.
+               select case (nfix_method)
+               case ('Houlton')
                  costNit(j,icostFix) = fun_cost_fix(fixer,&
                          a_fix(ivt(p)),b_fix(ivt(p)),c_fix(ivt(p)),&
                          big_cost,crootfr(p,j),s_fix(ivt(p)),tc_soisno(c,j))
-               elseif (nfix_method == 2) then
-                 ! Bytnerowicz no acclimation calculation
+               case ('Bytnerowicz')  ! no acclimation calculation
                  costNit(j,icostFix) = fun_cost_fix_Bytnerowicz_noAcc(fixer, &
                          nfix_tmin(ivt(p)),nfix_topt(ivt(p)),nfix_tmax(ivt(p)), &
                          big_cost,crootfr(p,j),s_fix(ivt(p)),tc_soisno(c,j))
-
-               endif
+               case default
+                  write(iulog,*) subname//' ERROR: unknown nfix_method value: ', nfix_method
+                  call endrun(msg=errMsg(sourcefile, __LINE__))
+               end select
 
             end do
             cost_fix(p,1:nlevdecomp)      = costNit(:,icostFix)

src/main/clm_varctl.F90

@@ -227,6 +227,8 @@ module clm_varctl
   !
   real(r8), public :: nfix_timeconst = -1.2345_r8 
 
+  character(len=25), public :: nfix_method  ! choice of nfix parameterization
+
   !----------------------------------------------------------
   ! Physics
   !----------------------------------------------------------

src/main/controlMod.F90

@@ -257,6 +257,8 @@ subroutine control_init(dtime)
          CNratio_floating, lnc_opt, reduce_dayl_factor, vcmax_opt, &
          CN_evergreen_phenology_opt, carbon_resp_opt
 
+    namelist /clm_nitrogen/ nfix_method
+
     namelist /clm_inparm/ use_soil_moisture_streams
 
     ! excess ice flag
@@ -882,6 +884,7 @@ subroutine control_spmd()
        call mpi_bcast (use_c13_timeseries,  1, MPI_LOGICAL, 0, mpicom, ier)
        call mpi_bcast (atm_c13_filename,  len(atm_c13_filename), MPI_CHARACTER, 0, mpicom, ier)
        call mpi_bcast (use_fun,            1, MPI_LOGICAL, 0, mpicom, ier)
+       call mpi_bcast (nfix_method, len(nfix_method), MPI_CHARACTER, 0, mpicom, ier)
     end if
 
     call mpi_bcast (perchroot, 1, MPI_LOGICAL, 0, mpicom, ier)