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carb_coefs.cbn

Purpose

carb_coefs.cbn holds the coefficients for the Century-style carbon and nitrogen cycling model. The reader populates carbdb, org_allo, org_frac, cb_wtr_coef, man_coef, org_con, and the soil-test layer table (sol_test). Values control passive and slow humus turnover, allocation to CO2 and the passive pool, organic-fraction initialization, soluble-carbon partitioning, tillage effect duration, manure-to-carbon conversion, temperature and water factor approaches, biomechanical mixing coefficients, and surface residue photodegradation.

Source

Activation

The reader runs only when bsn_cc%cswat == 1 (see codes.bsn). If the file is absent the flag carbon_coef_file stays .false. and the model falls back to compiled defaults.

Format

Keyword-value file. Order does not matter. Each record begins with a keyword. The reader skips one title line at the top of the file, then reads keywords until end of file. Lines starting with # are treated as comments.

Two-value keywords give the surface layer value first, the subsurface (all other layers) value second.

Keyword Values Target field Units Description
cbn_diagnostics 1 int cbn_diagnostics 0 or 1 extra carbon output files when set to 1
hp_rate 2 real carbdb(1:2)%hp_rate 1/day passive humus transformation rate
hs_rate 2 real carbdb(1:2)%hs_rate 1/day slow humus transformation rate
microb_rate 2 real carbdb(1:2)%microb_rate 1/day microbial biomass transformation rate
meta_rate 2 real carbdb(1:2)%meta_rate 1/day metabolic litter transformation rate
str_rate 2 real carbdb(1:2)%str_rate 1/day structural litter transformation rate
microb_top_rate 2 real carbdb(1:2)%microb_top_rate 1/day top-layer microbial activity adjustment
hs_hp 2 real carbdb(1:2)%hs_hp none slow-to-passive humus allocation
a1co2 2 real org_allo(1:2)%a1co2 fraction decomposed metabolic and passive pools to CO2
asco2 2 real org_allo(1:2)%asco2 fraction decomposed slow humus to CO2
apco2 2 real org_allo(1:2)%apco2 fraction decomposed passive humus to CO2
abco2 2 real org_allo(1:2)%abco2 fraction decomposed microbial biomass to CO2
org_frac 4 real org_frac%frac_seq, frac_hum_microb, frac_hum_slow, frac_hum_passive fraction initial allocation of soil carbon to pools
prmt_21 1 real cb_wtr_coef%prmt_21 none KOC for carbon loss in water and sediment (500-1500)
prmt_44 1 real cb_wtr_coef%prmt_44 0..1 ratio of soluble C in runoff to percolate
till_eff_days 1 real till_eff_days days days a tillage event remains effective
rtof 1 real man_coef%rtof none manure organic N and P partitioning between fresh and stable pools
cbn_consolidation_factors 2 real bio_consf, till_consf none biological and tillage moisture consolidation factors
cbn_factor_approaches 2 int org_con%tmpf, org_con%watf none temperature factor (1-3) and water factor (1-2) approaches used in cbn_zhang2.f90
tn 1 real org_con%tn deg C minimum temperature bound for tmpf2
top 1 real org_con%top deg C optimum temperature for tmpf2
tx 1 real org_con%tx deg C maximum temperature bound for tmpf2
zz_bmix_coefs 3 real zz_bmix_coef_a, b, c none biological mixing coefficients for mgt_tillfactor.f90 tillf option 4
zz_emix_coefs 3 real zz_emix_coef_a, b, c none tillage mixing coefficients for mgt_tillfactor.f90 tillf option 4
photo_degrade_factor 1 real photo_degrade_factor none surface residue photodegradation factor
nmbr_soil_test_layers 1 int nmbr_soil_test_layers none number of soil_test rows that follow. Must appear before any soil_test line
soil_test 1 char + 6 real sol_test%snam, d, bd, cbn, sand, silt, clay mixed one row per soil test layer (name, depth, bulk density, carbon, sand, silt, clay)

Unknown keywords produce a warning in simulation.out and are ignored.

Example

refdata/Ames_sub1/carb_coefs.cbn:

File: carb_coefs.cbn   Carbon coefficients used if cswat == 2 or cswat == 3

# cbn_diagnostics contols what carbon related files are printed out if hru_cb is specified in print.prt
cbn_diagnostics 0

# carbdb coefficients
#               1st_lyr     other_lyrs
hp_rate         1.2e-05     1.2e-05
hs_rate         2.92e-04    1.81e-04
microb_rate     0.0164      0.02
meta_rate       0.0405      0.0507
str_rate        0.0107      0.0134
microb_top_rate 0.0164      0.02
hs_hp           0.05        0.05

# org_allo coefficients
a1co2           0.60        0.55
asco2           0.55        0.55
apco2           0.55        0.55
abco2           0.55        0.0

# organic fractions used to initialize soil carbon into various pools
#               frac_seq    frac_hum_microb     frac_hum_slow   frac_hum_passive
org_frac        0.95        0.02                0.44            0.54

prmt_21         1000.
prmt_44         0.5
till_eff_days   100
rtof            0.5
cbn_consolidation_factors  .15        .10
cbn_factor_approaches   2       1
tn              -0.5
top             30.0
tx              50.0
zz_bmix_coefs   3.0    5.0   -5.5
zz_emix_coefs   3.0   15.0   -3.5
photo_degrade_factor    0.001
  • codes.bsn. The cswat switch selects whether this file is read.

Important

Potential bug. The header comment in the example file says the coefficients apply when cswat == 2 or cswat == 3. The reader in carbon_coef_read.f90 only opens the file when bsn_cc%cswat == 1. Setting cswat to 2 or 3 leaves carbon_coef_file = .false. and the compiled defaults are used regardless of what is written to carb_coefs.cbn.