EN - How to irrigate based on evaporation energy

EN - How to irrigate based on evaporation energy

    
Question

How to irrigate based on evaporation energy?

 Answer 

We place the plant in the central. We need to optimize the photosynthesis process. To do so we need to have focus more on crop level.




In general we define 3 balances. Irrigation on evaporation energy is related to the water balance.




One of the new trends is controlling on crop activity. This is particularly true for the conditioned cultivation in (semi) closed greenhouses and also for "Vertical Farming" in enclosed cultivation cells. From iSii version 7 with Plantvoice it is possible to set a target value for the crop activity in W/m². This makes this software well prepared for the future.

Energy from different sources contribute to crop activity, and therefore to evaporation. Irrigation on radiation sum in summer is a clear example. What is new is that we can now include other sources of energy to reach a total sum of evaporation energy. The big advantage is that irrigation is well matched to the plants’ needs even when the sun is not the dominant source of energy, but for example assimilation lighting. And that other contributing factors to additional evaporation are also included.



Evaporation energy: input: ViP
In the evaporation energy: supply ViP one or more of the factors contributing to evaporation can be translated to W/m² and therefore to their effective contribution to evaporation.




With crops that require coating or screening, or where lighting is used, a PAR measurement in the greenhouse is often a better measure for the evaporation energy than a radiation sensor outside the greenhouse.

Example 1: Irrigation on radiation sum (with evaporation energy in the background)

To gain experience with irrigation on evaporation energy it is advisable to do the irrigation on radiation sum as usual, but to run irrigation on evaporation energy in the background. A graph can show the differences between the two methods.
  • Choose also for "evaporation energy" under "start and stop conditions"
  • Select the same start and end times as when starting on radiation sum
  • Set the evaporation energy threshold high so that there will not be a start on this condition
  • Create a chart containing radiation sum and the evaporation energy sum of the individual crop section
Example 2: Irrigation based on radiation from the sun

Setting example with 100% light interception by the crop. The classic control of radiation sum (outside) can be replaced, if desired, by controlling on evaporation energy (inside).



The above example shows that outside radiation between 0 to 1000 W/m² translates into an energy input in the greenhouse of 0 to 700 W/m². This corresponds to the light transmission of 70% of a normal single glass greenhouse roof.

Advantage: more accurate irrigation
If for example we have a special greenhouse roof with AR coating and possibly a diffuse coating, we can modify this relationship. We can also when closing a shadow screen, reduce a part of the incoming radiation because the crop will receive less energy than with an open screen. Watering on evaporation energy makes it possible to tune the irrigation much more accurate to the actual conditions.



Example 3: Irrigation on measured PAR

Setting example with 100% light interception by the crop.



Explanation: If a PAR meter is present in the greenhouse, this will measure the radiation from both the sunlight as well as from the assimilation. The irrigation will now take both energy flows account.

Example 4: Combination of sunlight and lighting



Explanation: This method is useful when there is no PAR meter present in the greenhouse. This setting example assumes that 70% of the sunlight reaches the crop and the lighting contributes 80 W/m² to the evaporation energy. This irrigation is then tuned to these values.


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