MODELLING CARBON
FLOWS IN CROP AND SOIL
Krisztina R. Végh
Carbon and Nitrogen flows and storage
Eckersten, 1994)
Carbon flows in the CoupModel
Organic residues: surface litter,
C/N:20-80
C/N:10-30
rhizodeposition: 900-3000 kg C/ha
Dissolved organics
(Jansson, 2004)
C input: crop growth
3 approaches for the simulation of plant growth :
Logistic growth:
C Atma  cn p f(E ta /E tp )N s pl,p(t)
the potential growth is a function of time
Water use efficiency C
Atm a   w E ta
growth is estimated from WUE and simulated transpiration
Light use efficiency C Atma  ε L f(Ta )f(CN leaf )f(E ta /E tp )Rs pl
light use efficiency is used to estimate potential growth rate,
limited by unfavorable temperature, water and N conditions.
Allocation of assimilated C to the different plant parts
Plant biomass is divided into compartments of carbon
(CLeaf, CStem, CRoot, Cgrain Cmobile)
Different response functions of C allocation to roots from above
ground mass
shoot mass,
water stress,
leaf C:N
f ( Eta / Etp )  rwc1  rwc 2  ( Eta / Etp )
Options:
rMc 1
linear function
exponential
independent
Original parameters
doubled: rwc 1 rMc 1
rwc 2 rMc 2
rMc 3
f ( M )  rMc 1  rMc 2  e rMc 3 . M
Decomposition and mineralization – Soil organismsm are implicit
The decomposition is substrate controlled and calculated as a first
C decomp  k1 f(T)f (  )C litter
order rate process:
The relative amounts of
decomposition products
When soil organisms are
implicit, the soil profile
includes maximum of
three carbon pools with
specific decomposition
rates kl, kf, kh.
The three rate constants
are affected by response
functions
for
soil
moisture
(f)
and
temperature (fT).
Efficiency parameter fe determines the
fraction of C that is not released from
the soil as CO2
Organic carbon pools and carbon flows in the soil
Estimated consumption
rate of microbes with their
efficiency explicitly taken
into account + respiration
of microbial biomass
subpools
fraction of microbes located in the different pools
Decomposition
:
Substrate
dependence,
CN ratio
Scons: substrate half rate
concentration
Decomposition :
Substrate
dependence,
Carbon
contentration
The affects of parameters TemQ10 and
TemQ10Bas affect the response function
Q10 temp. response function with a threshold
value
Conclusions
Simulation models help to understand the mechanistic
relationships between SOC and soil – plant interactions
C flows and OC pools are similarly conceptualized in
several models. Simple switches to obtional pools, the
possibility of the use of different allocation functions
and several abiotic response functions help to describe
the processes that interact simultaneously to control C
dynamics in crop and soil.