Soil organic matter

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FORGEM

The soil sub-module used in ForGEM is based on the CENTURY dynamic terrestrial ecosystem model. CENTURY has been developed, tested and used over the past fifteen years to simulate the major pathways of carbon and nitrogen cycling of a multiple compartment organic matter sub model. (Parton et al., 1987, 1988, 1993, 1994; Kelly et al., 1993, Burke, 1997).

The plant production sub-model of CENTURY was replaced by the production sub-model of ForGEM.

Water availability and flow through the system is simulated using a simplified water budget model which is mostly determined by soil texture and depth.


Also see: soil parameters

flow diagram

Soil carbon flowdiagram.png

Figure 1. Flow diagram for Century soil organic C-model (from: Parton et al. 19xx)


formularium

AboveGroundLitter.Structure (i=1)

AboveGroundLitter.Metabolic (i=5)



BelowGroundLitter.Structure (i=2)







BelowGroundLitter.Metabolic (i=6)



AboveGroundLitter.Microbe (i=4)



BelowGroundLitter.Microbe (i=3)

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("<p>There was a problem during the HTTP request: 502 Bad Gateway </p>") from server "http://mathoid.testme.wmflabs.org":): \begin{array}{rl} {\frac{dC}{dt} &=\left(1-0.55\right)\cdot K_{2} \cdot L_{c} \cdot A\cdot BelowGroundLitter.Structure.C_{C}} \\ &+ \left(1-0.55\right)\cdot K_{6} \cdot A\cdot BelowGroundLitter.Metabolic.C} \\ &+ \left(1-C_{SP} -0.55\right)\cdot K_{7} \cdot A\cdot SlowSOM.C} \\ &+ \left(1-0.55\right)\cdot K_{8} \cdot A\cdot PassiveSOM.C} \\ &- \left(1-F_{T} \right)\cdot K_{3} \cdot T_{M} \cdot A\cdot C} \\ \\ \frac{dCO2}{dt} &=F_{T} \cdot K_{3} \cdot T_{M} \cdot A\cdot C \end{array}



SlowSOM (i=7)

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("<p>There was a problem during the HTTP request: 502 Bad Gateway </p>") from server "http://mathoid.testme.wmflabs.org":): \begin{array}{rl} {\frac{dC}{dt} &=\left(1-0.3\right)\cdot K_{1} \cdot A\cdot L_{C} \cdot SurfaceLitter.Structure.C_{L}} \\ &+ \left(1-0.6\right)\cdot K_{4} \cdot A\cdot Surface.Microbe.C \\ &+ \left(1-0.3\right)\cdot K_{2} \cdot A\cdot L_{C} \cdot BelowGroundLitter.Structure.C_{L} \\ &+ C_{AS} \cdot K_{3} \cdot A\cdot T_{M} \cdot BelowGround.Microbe.C} \\ &- \left(1-0.55\right)\cdot C_{SP} \cdot K_{7} \cdot A\cdot C} \\ \\ \frac{dCO2}{dt} &=\, 0.55\cdot C_{SP} \cdot K_{7} \cdot A\cdot C \end{array}



PassiveSOM (i=8)



Leached



Effect of soil texture on active SOM turnover

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("<p>There was a problem during the HTTP request: 502 Bad Gateway </p>") from server "http://mathoid.testme.wmflabs.org":): \begin{array}{rl} {T_{m} &=1-0.75\cdot T} \\ \\ {T &= T_{c} +T_{s} } \end{array}



Impact of lignin content of structural material (LS) on structural decomposition



Effect of abiotic environment (temperature, t, and water, W)

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("<p>There was a problem during the HTTP request: 502 Bad Gateway </p>") from server "http://mathoid.testme.wmflabs.org":): \begin{array}{rl} {t_{1} &=\frac{45-t_{s} }{45-35} } \\ \\ {t_{2} &=\exp ^{0.076\cdot \left(1-t_{1} ^{2.63} \right)} } \\ \\ {A_{t} &=t_{1} ^{0.2} \cdot t_{2} } \\ \\ {A_{W} &=\begin{cases} RAT<=1.5 \longrightarrow \frac{1}{1+30\cdot \exp ^{-8.5\cdot RAT} } \\ \\ RAT \ >\ 1.5 \longrightarrow {1-0.7\cdot \frac{RAT-1.5}{1.5} } \\ \end{cases} \\ \\ A&=A_{t} \cdot A_{w} \end{array}



Fractions of flows out active SOM (=BelowGroundLitter.Microbe.C)



Fractions of flows out slow SOM

to passive SOM pool

to active pool (BelowGroundLitter.Microbes)

References

Parton, W.J., Ojima, D.S., Cole, C.V., Schimel, D.S., 1994. A general model for soil organic matter dynamics: sensitivity to litter chemistry, texture and management. Quantitative Modeling of Soil Forming Processes.: 147-167.




Parton, W.J., Schimel, D.S., Cole, C.V., Ojima, D.S., 1986. Analysis of factors controlling soil organic matter levels in Geat Plains grasslands. Soil Sci. Soc. Am. J. 51: 1173-1179.




Parton, W.J., Scurlock, J.M.O., Ojima, D.S., Gilmanov T.G., Scholes R.J., Schimel, D.S., Kirchner, T., Menaut, J-C, Seastedt, T., Garcia Moya, E., Kamnalrut, A., Kinyamario, J.I., 1993. Observations and modeling of biomass and organic matter dynamics for the grassland bioma worldwide. Global Biogeochemical cycles 7(4): 785-809.




Parton, W.J., Stewart, J.W.B., & Cole C.V., 1988. Dynamics of C, N, P and S in grassland soils: a model. Biogeochemistry 5: 109-131.




acronym table

acronym desciption dimension value reference
A Combined abiotic impactfactor of soil moisture and soil temperature
At Effect of temperature on decomposition rate 0-1
AW Effect of water on decomposition rate 0-1
CL Structural C in lignin
CC Structural C in cellulose
CAL Fraction C lost due to organic leaching 0-1
CAP Fraction C allocated to passive SOM 0-1
CAS Fraction C send to slow SOM 0-1
CSP Fraction C allocated to passive SOM 0-1
CSA Fraction C allocated to active SOM 0-1
FM Fraction of litter that is metabolic 0-1
FT fraction C lost due to microbial respiration 0-1
i=1 AboveGround residue structural material
i=2 Soil plant residue structural material
i=3 Active SOM (soil microbes)
i=4 AboveGround microbes
i=5 AboveGround metabolic material
i=6 Soil plant residue metabolic material
i=7 Slow SOM fraction
i=8 Passive SOM fraction
Ki Maximum decomposition rate parameter of: Yr-1
K1 AboveGround residue structural material 3.9 (Parton 1994)
K2 Soil plant residue structural material 4.9 (Parton 1994)
K3 Active SOM (soil microbes) 7.3 (Parton 1994)
K4 AboveGround microbes 6.0 (Parton 1994)
K5 AboveGround metabolic material 14.8 (Parton 1994)
K6 Soil plant residue metabolic material 18.5 (Parton 1994)
K7 Slow SOM fraction 0.20 (Parton 1994)
K8 Passive SOM fraction 0.0045 (Parton 1994)
LC
LN Lignin to N ratio
LS Fraction of structural C that is lignin
T Tc + Ts
Tc Clay content Fraction
TM Effect of soil texture on active SOM turnover
Ts Sand content Fraction
tS Soil temperature C