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net.simplace.sim.components.experimental.intercropping.SplitWaterUptake

The water uptake per layer is split between the two crops proportionally to the given factors per layer.

Under some circumstances (e. g. when water demand is fulfilled by lower layers, where only one plant has roots), one plant would get more water than needed. In this case, the surplus can be redistributed partially (i. e. from those layers, where both plants have roots) to the other plant.

The module is designed to work with layered water models like SlimWater or Hillflow1D, that calculate water uptake per layer from mobile water and retained water fraction.

Calculation

Let \(f_{1,i}, f_{2,1}\) the allocation factors of layer \(i\) for plant 1 and 2, \(W_{i}\) the water uptake per layer due to the common demand and root distributions and \(P_1, P_2\) the potential transpiration of the two crops. Note that the potential transpiration for each crop is scaled to the fractions covered by each crop.

The actual water uptake per layer for both crops \(A_{1,i}, A_{2,i}\) are then calculated by

\[ A_{1,i} = \frac{f_{1,i}}{f_{1,i}+f_{2,i}} \cdot W_i \\ A_{2,i} = \frac{f_{2,i}}{f_{1,i}+f_{2,i}} \cdot W_i \]

and the actual transpirations are the sums over all layers

\[ A_1 = \sum_i A_{1,i} \quad \quad A_2 = \sum_i A_{2,i} \]

If the one of the uptake ratios

\[ u_1 = \frac{A_1}{P_1} \quad \quad u_2 = \frac{A_2}{P_2} \]

is bigger than 1 (i. e. the uptake would be higher than the demand),

then the actual water uptake per layer is reduced proportionally over all layers:

\[ A_{k,i} = \frac{1}{u_k} \cdot A_{k,i} \quad k=1 \quad \text{or} \quad k=2 \]

and the surplus per layer \(s_{k,i}\) is the difference of old and corrected uptake.

If cRedistributeBetweenPlants is set to true (the default), then the surplus is given to the other plant for those layers, where the allocation factor is nonzero (i. e. there are roots).

\[ A_{l,i} = A_{l,i} + s_{k,i} \quad \text{where} \quad k=1, l=2 \quad \text{or} \quad k=2, l=1 \]

If the corrected actual uptake per layer for both crops is lower than the initial uptake, then the unused water per layer is calculated. Unused water is left first in the retained fraction, and if there is still too much, the rest goest to mobile fraction of unused water.

References

Component Variables