Substrates: coir & rockwool
control options for Priva computers
Every Priva irrigation computer has the facility to alter the frequency of watering automatically from one or a combination of triggers based on time, the prevailing weather, or measurements from a sensor of one kind or another. But when it comes to the irrigation of substrates, three principle methods are in common use:
- Radiation sum (RadSum) is the starting point for ensuring that the frequency of irrigation adjusts automatically to the prevailing weather. A sensor measuring light or (ideally) radiation will trigger the irrigation cycle when the amount of accumulated radiation reaches a preset level. Used well, RadSum will give excellent irrigation control.
- Vapour Pressure Deficit (VPD) is an indication of the difference between the humidity at the leaf stomata and the surrounding air (and therefore of the transpiration rate and need for irrigation.) Last year's article on the subject gives more information about VPD with coir here.
- Moisture measurement:
- Sensors embedded in the slab. Growers are divided about whether moisture sensors perform reliably and consistently. In the case of coir, it seems to be especially difficult to measure moisture content accurately.
- Slab weight. Trays containing one or more slabs are mounted on electronic load cells which record the combined weight of the growing medium, the crop and the water content. The measured weight changes continuously depending on water lost to transpiration and drain, or added by irrigation, and also by changes in the weight of the crop itself as fruit matures and is harvested.
Most advisers now agree that judging the frequency and quantity of irrigation to substrates is the key to bumper crops. Used well, the systems described above do a very good job of controlling irrigation frequency.
Now, Priva have developed an integrated solution - the Root Optimiser - which combines several technologies to ensure that both the frequency and overall quantity of irrigation is precisely controlled.
The amount of water a plant needs ultimately depends on the transpiration rate. Root Optimiser calculates transpiration from all the climate information the Priva computer routinely gathers.
By combining this information with the reduced weight of the slab due to actual transpiration and adjusting for the addition of water during irrigation cycles and loss of water due to drain, Root Optimiser has all the information it needs to irrigate at exactly the right time and to control the amount of drain very precisely.
Smart software filters out weight disturbances due to crop work and picking, leaving only the weight due to changes in the water content of the slab in the control algorithm.
Root Optimiser settings can be made for up to 6 periods in the day, so that drain can be reduced or eliminated altogether at night. A full description of the Root Optimiser system can be viewed or downloaded in the following brochure.