Add maxlai_triggers_grainfill option.

Default .true. preserves old behavior.

bld/CLMBuildNamelist.pm

@@ -4288,6 +4288,7 @@ sub setup_logic_cropcal_streams {
   add_default($opts, $nl_flags->{'inputdata_rootdir'}, $definition, $defaults, $nl, 'flush_gdd20');
   add_default($opts, $nl_flags->{'inputdata_rootdir'}, $definition, $defaults, $nl, 'generate_crop_gdds');
   add_default($opts, $nl_flags->{'inputdata_rootdir'}, $definition, $defaults, $nl, 'use_mxmat');
+  add_default($opts, $nl_flags->{'inputdata_rootdir'}, $definition, $defaults, $nl, 'maxlai_triggers_grainfill');
   add_default($opts, $nl_flags->{'inputdata_rootdir'}, $definition, $defaults, $nl, 'stream_meshfile_cropcal');
 
   # These can't both be true

bld/namelist_files/namelist_defaults_ctsm.xml

@@ -605,6 +605,7 @@ attributes from the config_cache.xml file (with keys converted to upper-case).
 
 <generate_crop_gdds                                        >.false.</generate_crop_gdds>
 <use_mxmat                                                 >.true.</use_mxmat>
+<maxlai_triggers_grainfill                                 >.true.</maxlai_triggers_grainfill>
 
 <!-- use additional stress deciduous onset trigger    -->
 <constrain_stress_deciduous_onset               >.true.</constrain_stress_deciduous_onset>

bld/namelist_files/namelist_definition_ctsm.xml

@@ -1398,6 +1398,11 @@ Set to .true. in order to override crop harvesting logic and to instead harvest
 Set to .false. in order to ignore crop PFT parameter for maximum growing season length (mxmat). Must be set to .false. when generate_crop_gdds is .true.
 </entry>
 
+<entry id="maxlai_triggers_grainfill" type="logical" category="physics"
+        group="cnphenology" valid_values="" value=".true.">
+Set to .false. in order to disable behavior where crops enter grain-filling phase upon reaching max LAI
+</entry>
+
 <entry id="min_critical_dayl_method" type="char*25" category="physics"
        group="cnphenology" valid_values="Constant,DependsOnLat,DependsOnVeg,DependsOnLatAndVeg">
 Method for determining what the minimum critical day length for seasonal decidious leaf offset depends on

cime_config/testdefs/testlist_clm.xml

@@ -1393,6 +1393,15 @@
       <option name="comment"  >Repeat ERP_Ly3_P64x2...cropMonthOutput test with matrixcnOn</option>
     </options>
   </test>
+  <test name="ERP_Ly3_P64x2" grid="f10_f10_mg37" compset="IHistClm60BgcCrop" testmods="clm/cropMonthOutput--clm/NoMaxLaiGrainFillTrigger">
+    <machines>
+      <machine name="derecho" compiler="intel" category="aux_clm"/>
+    </machines>
+    <options>
+      <option name="wallclock">01:40:00</option>
+      <option name="comment"  >Repeat ERP_Ly3_P64x2...cropMonthOutput test without max LAI trigering grain fill</option>
+    </options>
+  </test>
   <test name="ERI_D_Ld9" grid="f10_f10_mg37" compset="I1850Clm45Bgc" testmods="clm/default">
     <machines>
       <machine name="derecho" compiler="gnu" category="aux_clm"/>

cime_config/testdefs/testmods_dirs/clm/NoMaxLaiGrainFillTrigger/user_nl_clm

@@ -0,0 +1,2 @@
+maxlai_triggers_grainfill = .false.
+

src/biogeochem/CNPhenologyMod.F90

@@ -146,6 +146,7 @@ module CNPhenologyMod
   real(r8)         :: min_gddmaturity = 1._r8     ! Weird things can happen if gddmaturity is tiny
   logical,  public :: generate_crop_gdds = .false. ! If true, harvest the day before next sowing
   logical,  public :: use_mxmat = .true.           ! If true, ignore crop maximum growing season length
+  logical,  public :: maxlai_triggers_grainfill = .true.   ! If true, crops will enter cphase_grainfill upon reaching maximum LAI
 
   ! For use with adapt_cropcal_rx_cultivar_gdds .true.
   real(r8), parameter :: min_gdd20_baseline = 0._r8  ! If gdd20_baseline_patch is ≤ this, do not consider baseline.
@@ -200,7 +201,7 @@ subroutine CNPhenologyReadNML( NLFilename )
     !-----------------------------------------------------------------------
     namelist /cnphenology/ initial_seed_at_planting, onset_thresh_depends_on_veg, &
                            min_critical_dayl_method, generate_crop_gdds, &
-                           use_mxmat
+                           use_mxmat, maxlai_triggers_grainfill
 
     ! Initialize options to default values, in case they are not specified in
     ! the namelist
@@ -226,6 +227,7 @@ subroutine CNPhenologyReadNML( NLFilename )
     call shr_mpi_bcast (min_critical_dayl_method,     mpicom)
     call shr_mpi_bcast (generate_crop_gdds,          mpicom)
     call shr_mpi_bcast (use_mxmat,                   mpicom)
+    call shr_mpi_bcast (maxlai_triggers_grainfill,   mpicom)
 
     if (      min_critical_dayl_method == "DependsOnLat"       )then
        critical_daylight_method = critical_daylight_depends_on_lat
@@ -2434,7 +2436,7 @@ subroutine CropPhenology(num_pcropp, filter_pcropp                     , &
             ! enter phase 2 onset for one time step:
             ! transfer seed carbon to leaf emergence
 
-            if (peaklai(p) >= 1 .and. hui(p) < huigrain(p)) then
+            if (maxlai_triggers_grainfill .and. peaklai(p) >= 1 .and. hui(p) < huigrain(p)) then
                hui(p) = huigrain(p)
                crop_inst%maxlai_triggered_grainfill_patch(p) = .true.
             endif