CSR plant rates

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As any model component, the PlantCohort receives a calculateRates-request when it is to update the integration rates for the current time step.

The subsequent caltulation steps are:

calculate the potential assimilation given the present radiation and competition

This step is delegated to the Light model for the concurrent calculation of the absorbed radiation by all the plants on the patch.

 lightmodel.dailyAssimilationTranspirationAndConductance(plantCohort)

This method does a Gaussian integration (3 steps of time) over _instantaneousAssimilationTranspirationAndConductance(), which essentially corresponds to FORGRO's ASSMTRAN.

The light-model is a Canopy model that has a list of all plants and layers on the patch. The inter-plant and intra-plant competition only steps in while determining the cumulative LAI. From this, all the radiation components are calculated. The potential assimilations then are calculated for both sunlit and shadowed leaves, which subsequently are balanced according to a fraction sunlit leaves (FSLLA).

determine the potential net production

determine the concommittant water uptake

Citing from Durigon et al., 2012.

Transpiration is limited by the soil water availability. This reduction is realized by multiplying the potential transpiration with Feddes' reduction function. Actual uptake per layer is calculated by multiplying Sz, max by the value of the water stress reduction function αz (0 ≤ αz ≤ 1) in the respective layer:



where Sz (m3 m-3 d-1) is the actual root water uptake for layer z.


Four typical pressure heads — h1, h2, h3 and h4 — parameterize αz(h) and delimit five specific ranges of uptake. Root water uptake is limited between h1 and h2 by oxygen deficiency, and between h3 and h4 by decreased water availability. The Feddes model uses low (h3l) and high (h3h) values of h3 to differentiate between low (Tl) and high (Th) atmospheric demands and potential transpiration rates. Commonly utilized values are Tl = 1 mm d-1 and Th = 5 mm d-1. For intermediate potential transpiration rates, the value of h3 actually used was linearly interpolated between h3l and h3h

Feddes1978.jpg

(after: Durigon et al., 2012)

When no specific values are supplied, then the calculation proceeds with the following defaults:

h1 pressure head at saturation
h2 pressure head at field capacity
h4 pressure head at permanent wilting point
h3l
h3h


See also CSR Soil Water

scale the actual production to the available water

allocate the actual production over the AllocatableOrgans


references

Durigon et al., 2012. Pressure Heads and Simulated Water Uptake Patterns for a Severely Stressed Bean Crop. Vadose Zone Journal 11 get it.



Feddes, R.A., Kowalik, P.J., Zaradny, H., 1978. Simulation of field water use and crop yield. Simul. Monogr. Ser. Pudoc, Wageningen, The Netherlands.