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CE_RATIO_C.for
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!***********************************************************************
! CE_RATIO_C, subroutine for CENTURY-based SOM/residue module of DSSAT.
!
! Purpose: This subroutine calculates the C:N and C:P ratio of newly
! formed SOM.
!
! Revision history:
! 01/12/2004 AJG Made a separate subroutine by splitting this off from
! LITDEC_C and SOMDEC_C.
! 08/30/2004 AJG Corrected layout irregularities.
! 09/11/2006 AJG Changed equations for C:P ratios.
!
! Called: CENTURY
! Calls : --
************************************************************************
SUBROUTINE CE_RATIO_C (
& AMINRL, CES1M, CES1T, CES1X, CES21I, CES21M, !Input
& CES21S, CES21T, CES21X, !Input
& CES23LM, CES23LX, CES23M, !Input
& CES23T, CES23X, CES2LI, CES2LM, CES2LS, !Input
& CES2LX, CES3M, CES3T, CES3X, DLAYR, L, METABC, !Input
& METABE, N_ELEMS, SOM1C, SOM1E, STRUCC, STRUCE, !Input
& CES1, CES21, CES23, CES23L, CES2L, CES3) !Output
! ------------------------------------------------------------------
USE ModuleDefs !Definitions of constructed variable types,
!which contain control information, soil
!parameters, hourly weather data.
IMPLICIT NONE
SAVE
! ------------------------------------------------------------------
INTEGER IEL, L, N_ELEMS
! INTEGER, PARAMETER :: NONLIG = 1, LIG = 2
INTEGER, PARAMETER :: SRFC = 0, SOIL = 1
REAL CEADD, CES1S, FREMET, FRESTR
REAL DLAYR(NL), METABC(0:NL), SOM1C(0:NL), STRUCC(0:NL)
REAL AMINRL(NL,3), CES1(0:NL,3), CES1M(0:1,3), CES1T(0:1,3),
& CES1X(0:1,3), CES21(0:NL,3), CES21I(0:0,3), CES21M(0:1,3),
& CES21S(0:1,3), CES21T(1,3), CES21X(0:1,3), CES23(0:NL,3),
& CES23L(0:NL,3), CES23LM(0:1,3),
& CES23LX(0:1,3), CES23M(0:1,3), CES23S(0:1,3),
& CES23T(1:1,3), CES23X(0:1,3), CES2L(0:NL,3), CES2LI(0:1,3),
& CES2LM(0:1,3), CES2LS(0:1,3), CES2LX(0:1,3), CES3(NL,3),
& CES3M(1,3),CES3S(1,3), CES3T(1,3), CES3X(1,3), METABE(0:NL,3),
& SOM1E(0:NL,3), STRUCE(0:NL,3)
! ------------------------------------------------------------------
!#######################################################################
! FOR LITDEC_C
!#######################################################################
! ------------------------------------------------------------------
! C/E ratio of surface SOM1 from surface metabolic.
! ------------------------------------------------------------------
DO IEL = 1, N_ELEMS
IF (IEL == N .AND. L == SRFC) THEN
! Fraction N in metabolic pool.
IF (METABC(SRFC) > 1.E-5) THEN
FREMET = METABE(SRFC,N) / (METABC(SRFC) * 2.5)
! If the N concentration of the decomposing surface metabolic
! residue is >= a threshold value, set the C/N ratio of the
! new surface SOM1 to the minimum value.
IF (FREMET >= CES1T(SRFC,N)) THEN
CES1(SRFC,N) = CES1M(SRFC,N)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/E ratio, depending on the E concentration of the
! decomposing surface metabolic residue.
CES1S = (CES1M(SRFC,N) - CES1X(SRFC,N)) / CES1T(SRFC,N)
CES1(SRFC,N) = CES1X(SRFC,N) + FREMET * CES1S
! Make sure that the new C/E ratio is >= the minimum and <=
! the maximum.
CES1(SRFC,N) = AMAX1 (CES1(SRFC,N), CES1M(SRFC,N))
CES1(SRFC,N) = AMIN1 (CES1(SRFC,N), CES1X(SRFC,N))
ENDIF !End of IF block on FREMET
ELSE
FREMET = 0.0
ENDIF !End of IF block on METABC(SRFC) > 1.E-5
ELSEIF (IEL == P .AND. L == SRFC) THEN
! Surface microorganisms are much more limited by C than by P.
! Thus, only if C is abundant (e.g. >200 kg/ha per 1-cm soil
! depth -- but the SRFC layer has no depth), P may become limiting.
IF (METABC(SRFC) > 0. .AND. METABC(SRFC) < 200.) THEN
! P is not limiting.
CES1(SRFC,P) = CES1M(SRFC,P)
ELSEIF (METABC(SRFC) >= 200.) THEN
! P may be limiting.
! If the P concentration of the decomposing surface metabolic
! residue is >= a threshold value, set the C/P ratio of the
! new surface SOM1 to the minimum value.
FREMET = METABE(SRFC,P) / (METABC(SRFC) * 2.5)
IF (FREMET >= CES1T(SRFC,P)) THEN
CES1(SRFC,P) = CES1M(SRFC,P)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/P ratio, depending on the P concentration of the
! decomposing surface metabolic residue.
CES1S = (CES1M(SRFC,P) - CES1X(SRFC,P)) / CES1T(SRFC,P)
CES1(SRFC,P) = CES1X(SRFC,P) + FREMET * CES1S
! Make sure that the new C/P ratio is >= the minimum value
! and <= the maximum.
CES1(SRFC,P) = AMAX1 (CES1(SRFC,P), CES1M(SRFC,P))
CES1(SRFC,P) = AMIN1 (CES1(SRFC,P), CES1X(SRFC,P))
ENDIF !End if IF block on FREMET.
ENDIF !End of IF block on METABC.
ENDIF !End of IF block on IEL
! -----------------------------------------------------------------
! C/E ratio of surface SOM1 and SOM2(N) or SOM23(P) of layer 1 from
! surface structural.
! -----------------------------------------------------------------
IF (IEL == N .AND. L == SRFC) THEN
! =====================
! nonlignin(N) --> SOM1
! =====================
! E concentration of the decomposing surface structural
! residue
IF (STRUCC(SRFC) > 1.E-5) THEN
FRESTR = STRUCE(SRFC,N) / (STRUCC(SRFC) * 2.5)
! If the N concentration of the decomposing surface structural
! residue is >= a threshold value, set the C/N ratio of the new
! surface SOM1 to the minimum value.
IF (FRESTR >= CES1T(SRFC,N)) THEN
CES1(SRFC,N) = CES1M(SRFC,N)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/N ratio, depending on the E concentration of the
! decomposing surface structural residue.
CES1S = (CES1M(SRFC,N) - CES1X(SRFC,N)) /
& CES1T(SRFC,N)
CES1(SRFC,N) = CES1X(SRFC,N) + FRESTR * CES1S
! Make sure that the new C/N ratio is >= the minimum value
! and <= the maximum.
CES1(SRFC,N) = AMAX1 (CES1(SRFC,N), CES1M(SRFC,N))
CES1(SRFC,N) = AMIN1 (CES1(SRFC,N), CES1X(SRFC,N))
ENDIF !End of IF block on FRESTR.
ELSE
FRESTR = 0.0
ENDIF !End of IF block on STRUCC(SRFC) > 1.E-5
! ==================
! lignin(N) --> SOM2
! ==================
! Calculate the C/N ratio for new SOM2 from decomposing
! lignin surface structural residue. This is set equal to
! the C/N of the surface SOM1 that is newly formed from the
! non-lignin structural residue, plus a factor that depends
! on the C/N of SOM1.
CEADD = CES2LI(SRFC,N) + CES2LS(SRFC,N) *
& (CES1(SRFC,N) - CES1M(SRFC,N))
CES2L(SRFC,N) = CES1(SRFC,N) + CEADD
! Make sure that the C/E ratio of the new SOM2 is >= the minimum
! value and <= the maximum.
CES2L(SRFC,N) = AMAX1 (CES2L(SRFC,N), CES2LM(SRFC,N))
CES2L(SRFC,N) = AMIN1 (CES2L(SRFC,N), CES2LX(SRFC,N))
ELSEIF (IEL == P .AND. L == SRFC) THEN
! =====================
! nonlignin(P) --> SOM1
! =====================
! Soil microorganisms are much more limited by C than by P.
! Thus, only if C is abundant (e.g. >200 kg[C]/ha per 1-cm soil
! depth -- but the SRFC layer has no depth), P may become limiting.
IF (STRUCC(SRFC) < 200.) THEN
! P is not limiting.
CES1(SRFC,P) = CES1M(SRFC,P)
ELSEIF (STRUCC(SRFC) >= 200.) THEN
! P may be limiting.
! If the P concentration of the decomposing surface structural
! residue is >= a threshold value, set the C/P ratio of the
! new surface SOM1 to the minimum value.
FRESTR = STRUCE(SRFC,P) / (STRUCC(SRFC) * 2.5)
IF (FRESTR >= CES1T(SRFC,P)) THEN
CES1(SRFC,P) = CES1M(SRFC,P)
ELSEIF (FRESTR > 0. .AND. FRESTR < CES1T(SRFC,P)) THEN
! Otherwise, interpolate between the minimum and maximum
! C/P ratio, depending on the P concentration of the
! decomposing surface structural residue.
CES1S = (CES1M(SRFC,P) - CES1X(SRFC,P)) / CES1T(SRFC,P)
CES1(SRFC,P) = CES1X(SRFC,P) + FRESTR * CES1S
! Make sure that the new C/P ratio is >= the minimum value
! and <= the maximum.
CES1(SRFC,P) = AMAX1 (CES1(SRFC,P), CES1M(SRFC,P))
CES1(SRFC,P) = AMIN1 (CES1(SRFC,P), CES1X(SRFC,P))
ENDIF !End of IF block on FRESTR
ENDIF !End of IF block on STRUCC.
! ========================
! SRFC lignin(P) --> SOM23
! ========================
! Calculate the C/P ratio for new SOM23 from decomposing
! soil structural lignin residue. This is set equal to
! the C/P of the soil SOM1 that is newly formed from the
! non-lignin soil residue, plus a factor.
!CENTURY (PREDEC) == SRFC lignin --> SOM2 of L=1
!radds1 = rad1p(1,iel) + rad1p(2,iel) * (rnewas(iel,1)-pcemic(2,iel))
!rnewas(iel,2) = rnewas(iel,1) + radds1
!rnewas(iel,2) = max(rnewas(iel,2), rad1p(3,iel))
!rnewas(iel,2) is new SOM2 from SRFC lignin; rad1p(1,iel) is intercept (220), rad1p(2,iel) is slope (5);
!pcemic(2,2) is minimum C/P ratio for surface microbes (99)
! From CENTURY's sub PREDEC:
! CEADD = 220 + 5 * SOM1C(L) / SOM1E(L,P) - 99
CEADD = 220 + 5 * CES1(SRFC,P) - 99
CES23L(SRFC,P) = CES1(SRFC,P) + CEADD
! Make sure that the C/E ratio of the new SOM23 is >= the minimum
! value and <= the maximum.
CES23L(SRFC,P) = AMAX1 (CES23L(SRFC,P), CES23LM(SRFC,P))
CES23L(SRFC,P) = AMIN1 (CES23L(SRFC,P), CES23LX(SRFC,P))
ENDIF !End of IF block on IEL
! ----------------------------------------------------------------
! C/E ratio of soil SOM1 from soil metabolic.
! ----------------------------------------------------------------
IF (IEL == N .AND. L /= SRFC) THEN
! NB: The original CENTURY model only deals with a 20-cm-thick
! soil layer, while DSSAT has many layers of variable thickness.
! The parameter CES1T (a 'fixed' parameter) is in kg[N]/ha
! and the comparison it is used for depends on the layer
! thickness. It is therefore recalculated to a 1-cm-thick layer.
IF (AMINRL(L,N) <= 1.E-06) THEN
! If no E available in the soil for immobilization by the
! residue, set the C/E ratio to the maximum value.
CES1(L,N) = CES1X(SOIL,N)
ELSEIF (AMINRL(L,N) / DLAYR(L) >=
& CES1T(SOIL,N) / 20.) THEN
! If the amount of E available in the soil for immobilization
! by the residue is more than the critical value, set the C/E
! ratio to the minimum value.
CES1(L,N) = CES1M(SOIL,N)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/E ratio, depending on the amount of E available in the
! soil for absorption by the residue.
CES1S = -(CES1X(SOIL,N) - CES1M(SOIL,N)) /
& (CES1T(SOIL,N) / 20.)
CES1(L,N) = CES1X(SOIL,N) + CES1S *
& AMINRL(L,N) / DLAYR(L)
! Make sure that the new C/E ratio is >= the minimum value
! and <= the maximum.
CES1(L,N) = AMAX1 (CES1(L,N), CES1M(SOIL,N))
CES1(L,N) = AMIN1 (CES1(L,N), CES1X(SOIL,N))
ENDIF !End of IF block on AMINRL
ELSEIF (IEL == P .AND. L /= SRFC) THEN
! Soil microorganisms are much more limited by C than by P.
! Thus, only if C is abundant (e.g. >200 kg[C] per 1-cm soil depth),
! P may become limiting.
IF (METABC(L) / DLAYR(L) < 200.) THEN
! P is not limiting.
CES1(L,P) = CES1M(SOIL,P)
ELSE !METABC(L) / DLAYR(L) >= 200.
! P may be limiting.
! If the P concentration of the decomposing surface metabolic
! residue is >= a threshold value, set the C/P ratio of the
! new surface SOM1 to the minimum value.
FREMET = METABE(L,P) / (METABC(L) * 2.5)
IF (FREMET >= CES1T(SOIL,P)) THEN
CES1(L,P) = CES1M(SOIL,P)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/P ratio, depending on the P concentration of the
! decomposing surface metabolic residue.
CES1S = (CES1M(SOIL,P) - CES1X(SOIL,P)) /
& (CES1T(SOIL,P) / 20.)
CES1(L,P) = CES1X(SOIL,P) + FREMET * CES1S
! Make sure that the new C/P ratio is >= the minimum value
! and <= the maximum.
CES1(L,P) = AMAX1 (CES1(L,P), CES1M(SOIL,P))
CES1(L,P) = AMIN1 (CES1(L,P), CES1X(SOIL,P))
ENDIF !End of IF block on FREMET.
ENDIF !End of IF block on METABC
ENDIF !End of IF block on IEL.
! ----------------------------------------------------------------
! C/E ratio of soil SOM1 and SOM2 or SOM23 from soil structural.
! ----------------------------------------------------------------
IF (IEL == N .AND. L /= SRFC) THEN
! =====================
! nonlignin(N) --> SOM1
! =====================
! NB: The original CENTURY model only deals with a 20-cm-thick
! soil layer, while DSSAT has many layers of variable thickness.
! The parameter CES1T (a 'fixed' parameter) is in kg[N]/ha
! and the comparison it is used for depends on the layer
! thickness. It is therefore recalculated to a 1-cm-thick layer.
! If the amount of E available in the soil for
! immobilization by the residue is more than the critical
! value, set the C/E ratio to the minimum value.
IF (AMINRL(L,N) / DLAYR(L) >=
& CES1T(SOIL,N) / 20.) THEN
CES1(L,N) = CES1M(SOIL,N)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/E ratio, depending on the amount of E available in the
! soil for absorption by the residue.
CES1S = -(CES1X(SOIL,N) - CES1M(SOIL,N)) /
& (CES1T(SOIL,N) / 20.)
CES1(L,N) = CES1X(SOIL,N) + CES1S *
& AMINRL(L,N) / DLAYR(L)
! Make sure that the new C/E ratio is >= the minimum value
! and <= the maximum.
CES1(L,N) = AMAX1 (CES1(L,N), CES1M(SOIL,N))
CES1(L,N) = AMIN1 (CES1(L,N), CES1X(SOIL,N))
ENDIF
! ==================
! soil lignin(N) --> SOM2
! ==================
! Calculate the C/E ratio for new SOM2 from decomposing
! soil structural lignin residue. This is set equal to
! the C/E of the soil SOM1 that is newly formed from the
! non-lignin soil residue, plus a factor that depends
! on the C/E of SOM1.
CEADD = CES2LI(SOIL,N) + CES2LS(SOIL,N) *
& (CES1(L,N) - CES1M(SOIL,N))
CES2L(L,N) = CES1(L,N) + CEADD
! Make sure that the new C/E ratio is >= the minimum value
! and <= the maximum.
CES2L(L,N) = AMAX1 (CES2L(L,N), CES2LM(SOIL,N))
CES2L(L,N) = AMIN1 (CES2L(L,N), CES2LX(SOIL,N))
ELSEIF (IEL == P .AND. L /= SRFC) THEN
! =====================
! nonlignin(P) --> SOM1
! =====================
! Soil microorganisms are much more limited by C than by P.
! Thus, only if C is abundant (e.g. >200 kg[C] per 1-cm soil depth),
! P may become limiting.
IF (STRUCC(L) / DLAYR(L) < 200.) THEN
! P is not limiting.
CES1(L,P) = CES1M(SOIL,P)
ELSE !STRUCC(L) / DLAYR(L) >= 200.
! P may be limiting.
! If the P concentration of the decomposing soil structural
! material is >= than a threshold value, set the C/P ratio of
! the new surface SOM1 to the minimum value.
FRESTR = STRUCE(L,P) / (STRUCC(L) * 2.5)
IF (FRESTR >= CES1T(SOIL,P)) THEN
CES1(L,P) = CES1M(SOIL,P)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/P ratio, depending on the P concentration of the
! decomposing soil structural residue.
CES1S = (CES1M(SOIL,P) - CES1X(SOIL,P)) /
& (CES1T(SOIL,P) / 20.)
CES1(L,P) = CES1X(SOIL,P) + FREMET * CES1S
! Make sure that the new C/P ratio is >= the minimum value
! and <= the maximum.
CES1(L,P) = AMAX1 (CES1(L,P), CES1M(SOIL,P))
CES1(L,P) = AMIN1 (CES1(L,P), CES1X(SOIL,P))
ENDIF !End of IF block on FRESTR.
ENDIF !End of IF block on STRUCC.
! ========================
! soil lignin(P) --> SOM23
! ========================
! Set the C/P ratio for new SOM23 from decomposing
! soil structural lignin residue.
! Set CES23L from soil lignin to CES23X, as in CENTURY's sub PREDEC (param VARAT2(1,2)).
CES23L(L,P) = CES23X(SOIL,P)
! Make sure that the C/E ratio of the new SOM2 is >= the minimum
! value and <= the maximum.
CES23L(L,P) = AMAX1 (CES23L(L,P), CES23LM(SOIL,P))
CES23L(L,P) = AMIN1 (CES23L(L,P), CES23LX(SOIL,P))
ENDIF !End of IF block on IEL.
!#######################################################################
! FOR SOMDEC_C
!#######################################################################
! ----------------------------------------------------------------
! C/E ratio of new SOM2(N) or SOM23(P) from decomposing surface SOM1.
! ----------------------------------------------------------------
IF (IEL == N .AND. L == SRFC) THEN
! Calculate C/E ratios for the flow from surface SOM1 to
! SOM2 (layer 1). The C/E of new SOM2 equals C/E of old
! surface SOM1 plus a factor that depends on the C/E of
! SOM1.
IF (SOM1E(SRFC,N) > 1.E-06) THEN
CEADD = CES21I(SRFC,N) + CES21S(SRFC,N) *
& (SOM1C(SRFC) / SOM1E(SRFC,N) - CES1M(SRFC,N))
CES21(SRFC,N) = SOM1C(SRFC) / SOM1E(SRFC,N) + CEADD
ENDIF
! Make sure that the new C/E ratio is >= the minimum value
! allowed and =< the maximum value allowed.
CES21(SRFC,N) = AMAX1 (CES21(SRFC,N), CES21M(SRFC,N))
CES21(SRFC,N) = AMIN1 (CES21(SRFC,N), CES21X(SRFC,N))
ELSEIF (IEL == P .AND. L == SRFC) THEN
IF (SOM1E(SRFC,P) > 1.E-06) THEN
!CENTURY = SRFC SOM1:
!radds1 = rad1p(1,iel) + rad1p(2,iel) * ((som1c(1)/som1e(1,iel)) - pcemic(2,iel)) !!SOM1C(1) is SRFC layer
! = 220 + 5 * ((som1c(1)/som1e(1,iel)) - 99
!rceto2(iel) = som1c(SRFC)/som1e(SRFC,iel) + radds1
!rad1p(1,1) is CES21I(0,2) = 220
!rad1p(2,1) is CES21S(0,2) = 5
!pcemic(2,2) is CES1M(0,2) = 99
CEADD = CES21I(SRFC,P) + CES21S(SRFC,P) *
& SOM1C(SRFC) / SOM1E(SRFC,P) - CES1M(0,P)
CES23(SRFC,P) = SOM1C(SRFC) / SOM1E(SRFC,P) + CEADD
ENDIF
! Make sure that the new C/E ratio is >= the minimum value
! allowed and =< the maximum value allowed.
CES23(SRFC,P) = AMAX1 (CES23(SRFC,P), CES23M(SRFC,P))
CES23(SRFC,P) = AMIN1 (CES23(SRFC,P), CES23X(SRFC,P))
ENDIF !End of IF block on IEL.
! ----------------------------------------------------------------
! C/E ratio of new soil SOM1 from decomposing SOM2, SOM3 or SOM23.
! ----------------------------------------------------------------
IF (IEL == N .AND. L /= SRFC) THEN
IF (AMINRL(L,N) <= 1.E-06) THEN
! If there is no mineral N available in the soil for
! absorption by the decomposing SOM2 or SOM3, set the C/N
! ratio of the new soil SOM1 to the maximum value allowed.
CES1(L,N) = CES1X(SOIL,N)
ELSEIF ((AMINRL(L,N) / DLAYR(L)) >= CES1T(SOIL,N)) THEN
! If the amount of mineral N available in the soil for
! absorption by the decomposing SOM2 or SOM3 is greater than
! the critical value, set the C/N ratio of the new soil SOM1
! to the minimum value allowed.
CES1(L,N) = CES1M(SOIL,N)
ELSE
! Otherwise, interpolate between the minimum and maximum C/N
! ratio depending on the amount of mineral N available in
! the soil for absorption by the decomposing SOM2 or SOM3.
CES1S = -(CES1X(SOIL,N) - CES1M(SOIL,N)) / CES1T(SOIL,N)
CES1(L,N) = CES1X(SOIL,N) + CES1S * AMINRL(L,N)
! Make sure that the new C/N ratio is >= the minimum value
! allowed and =< the maximum value allowed.
CES1(L,N) = AMAX1 (CES1(L,N), CES1M(SOIL,N))
CES1(L,N) = AMIN1 (CES1(L,N), CES1X(SOIL,N))
ENDIF !End of IF block on AMINRL.
ELSEIF (IEL == P .AND. L /= SRFC) THEN
IF (AMINRL(L,P) <= 1.E-06) THEN
! If there is no mineral P available in the soil for
! absorption by the decomposing SOM23, set the C/P
! ratio of the new soil SOM1 to the maximum value allowed.
CES1(L,P) = CES1X(SOIL,P)
ELSEIF ((AMINRL(L,P) / DLAYR(L)) >= CES1T(SOIL,P)) THEN
! If the amount of mineral P available in the soil per 1-cm soil
! depth for absorption by the decomposing SOM23 is greater than
! the critical value, set the C/P ratio of the new soil SOM1
! to the minimum value allowed.
CES1(L,P) = CES1M(SOIL,P)
ELSE
! Otherwise, interpolate between the minimum and maximum C/P
! ratio depending on the amount of mineral P available in
! the soil for absorption by the decomposing SOM2 or SOM3.
CES1S = -(CES1X(SOIL,P) - CES1M(SOIL,P)) / CES1T(SOIL,P)
CES1(L,P) = CES1X(SOIL,P) + CES1S * AMINRL(L,P)
! Make sure that the new C/P ratio is >= the minimum value
! allowed and =< the maximum value allowed.
CES1(L,P) = AMAX1 (CES1(L,P), CES1M(SOIL,P))
CES1(L,P) = AMIN1 (CES1(L,P), CES1X(SOIL,P))
ENDIF !End of IF block on AMINRL.
ENDIF !End of IF block on IEL.
! ----------------------------------------------------------------
! C/E ratio of new SOM2(N) or SOM23(P) from decomposing soil SOM1.
! ----------------------------------------------------------------
! NB: The original CENTURY model only deals with a 20-cm-thick
! soil layer, while DSSAT has many layers of variable thickness.
! The parameter CES21T (a 'fixed' parameter) is in kg[N]/ha
! and the comparison it is used for depends on the layer
! thickness. It is therefore recalculated to a 1-cm-thick layer.
IF (IEL == N .AND. L /= SRFC) THEN
IF (AMINRL(L,N) <= 1.E-06) THEN
! If there is no mineral N available in the layer for
! absorption by the decomposing soil SOM1, set the C/N ratio
! of the new SOM2 to the maximum value allowed.
CES21(L,N) = CES21X(SOIL,N)
ELSEIF (AMINRL(L,N) / DLAYR(L) > CES21T(SOIL,N) / 20.) THEN
! If the amount of mineral N available in the layer for
! absorption by the decomposing soil SOM1 is greater than
! the critical value, set the C/N ratio of the new SOM2 to
! the minimum value allowed.
CES21(L,N) = CES21M(SOIL,N)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/E, depending on the amount of mineral N available in
! the layer for absorption by the decomposing soil SOM1.
CES21S(SOIL,N) = -(CES21X(SOIL,N) - CES21M(SOIL,N))
& / (CES21T(SOIL,N) / 20.)
CES21(L,N) = CES21X(SOIL,N) + CES21S(SOIL,N) *
& AMINRL(L,N) / DLAYR(L)
! Make sure that the new C/N ratio is >= the minimum value
! allowed and =< the maximum value allowed.
CES21(L,N) = AMAX1 (CES21(L,N), CES21M(SOIL,N))
CES21(L,N) = AMIN1 (CES21(L,N), CES21X(SOIL,N))
ENDIF !End of IF block on CES21.
ELSEIF (IEL == P .AND. L /= SRFC) THEN
!================
!CENTURY soil SOM1:
!rceto2(iel) = bgdrat(aminrl,varat2,iel)
!bgdrat = (1.-aminrl(P)/varat(3,P)) * (varat(1,P)-varat(2,P))+varat(2,P)
!bgdrat = (1.-aminrl(P) / 2) * (400. - 100.) + 100.
!varat2(1,P) = maximum C/E ratio for material entering SOM2, thus SOM23X(1,2) = 400
!varat2(2,P) = minimum C/E ratio for material, thus SOM23M(1,2) = 100
!varat2(3,P) = amount of E present when minimum ratio applies, thus SOM23T(1,2) = 2 g/m2 or 20 kg/ha
!================
CES23(L,P) = (1. - AMINRL(L,P) / CES23T(1,P)) *
& (CES23X(1,P) - CES23M(1,P)) + CES23M(1,P)
CES23(L,P) = (1. - AMINRL(L,P) / 20.) * (400. - 100.) + 100.
IF (AMINRL(L,P) < 1.E-06) THEN
! If there is no mineral P available in the layer for
! absorption by the decomposing soil SOM1, set the C/P ratio
! of the new SOM23 to the maximum value allowed.
!================
!CENTURY:
!rceto2(iel) = bgdrat(aminrl,varat2,iel)
!bgdrat = varat(1,iel)
!================
CES23(L,P) = CES23X(SOIL,P)
ELSEIF (AMINRL(L,P) / DLAYR(L) > CES23T(SOIL,P) / 20.) THEN
! If the amount of mineral P available in the layer for
! absorption by the decomposing soil SOM1 is greater than
! the critical value, set the C/P ratio of the new SOM23 to
! the minimum value allowed.
!================
!CENTURY:
!elseif (aminrl(iel) .gt. varat(3,iel))
!bgdrat = varat(2,iel)
!================
CES23(L,P) = CES23M(SOIL,P)
ELSE
! Otherwise, interpolate between the minimum and maximum
! C/P, depending on the amount of mineral P available in
! the layer for absorption by the decomposing soil SOM1.
!================
!CENTURY:
!aminrl(iel) > 0 and <= varat(3,iel)
!bgdrat = (1.-aminrl(iel)/varat(3,iel))*(varat(1,iel)-varat(2,iel))+varat(2,iel)
!================
CES23S(SOIL,P) = -(CES23X(SOIL,P) - CES23M(SOIL,P))
& / (CES23T(SOIL,P) / 20.)
CES23(L,P) = CES23X(SOIL,P) + CES23S(SOIL,P) *
& AMINRL(L,P) / DLAYR(L)
! Make sure that the new C/P ratio is >= the minimum value
! allowed and =< the maximum value allowed.
CES23(L,P) = AMAX1 (CES23(L,P), CES23M(SOIL,P))
CES23(L,P) = AMIN1 (CES23(L,P), CES23X(SOIL,P))
ENDIF !End of IF block on AMINRL.
ENDIF !End of IF block on IEL.
! ----------------------------------------------------------------
! C/E ratio of new SOM3 from decomposing soil SOM1 or SOM2.
! ----------------------------------------------------------------
! NB: The original CENTURY model only deals with a 20-cm-thick
! soil layer, while DSSAT has many layers of variable thickness.
! The parameter CES3T (a 'fixed' parameter) is in kg[N]/ha
! and the comparison it is used for depends on the layer
! thickness. It is therefore recalculated to a 1-cm-thick layer.
IF (IEL == N .AND. L /= SRFC) THEN
IF (AMINRL(L,N) <= 1.E-06) THEN
! If there is no mineral E available in the layer for
! absorption by the decomposing soil SOM1 or SOM2, set the
! C/E ratio of the new SOM3 to the maximum value allowed.
CES3(L,N) = CES3X(SOIL,N)
ELSEIF (AMINRL(L,N) / DLAYR(L) > CES3T(SOIL,N) / 20.) THEN
! If the amount of mineral E available in the layer for
! absorption by the decomposing soil SOM1 or SOM2 is greater
! than the critical value, set the C/E ratio of the new SOM3
! to the minimum value allowed.
CES3(L,N) = CES3M(SOIL,N)
ELSE
! Otherwise, interpolate between the minimum and maximum C/E
! ratio depending on the amount of mineral E available in
! the layer for absorption by the decomposing soil SOM1 or
! SOM2.
CES3S(SOIL,N) = -(CES3X(SOIL,N) - CES3M(SOIL,N)) /
& (CES3T(SOIL,N) / 20.)
CES3(L,N) = CES3X(SOIL,N) + CES3S(SOIL,N) *
& AMINRL(L,N) / DLAYR(L)
! Make sure that the new C/E ratio is >= the minimum value
! allowed and =< the maximum value allowed.
CES3(L,N) = AMAX1 (CES3(L,N), CES3M(SOIL,N))
CES3(L,N) = AMIN1 (CES3(L,N), CES3X(SOIL,N))
ENDIF !End of IF block on CES3.
ELSEIF (IEL == P .AND. L /= SRFC) THEN
! Nothing needed, as CE23(L,P) has already been calculated.
ENDIF !End of IF block on IEL.
ENDDO !End of loop on IEL.
RETURN
END Subroutine CE_RATIO_C