EC management is easier in steerable substrates due to better irrigation efficiency.
Achieving drain each and every day and realizing average 24 hour drain figures >30% to manage EC is a thing of the past for the modern greenhouse grower. There are economic and legislative drivers to consider why this philosophy should be adopted to realize Precision Growing:
- The additional cost of energy required to stimulate transpiration in order to steer the vegetative – generative plant balance and to control humidity as a result of over supplying water to the plant on dark days.
- The direct cost of unnecessarily applying water and fertilizer to “chase” and stabilize substrate EC.
- The need to manage (prevent) nutrient discharge from the greenhouse.
In this technical article we describe the principle of irrigation efficiency and how this design feature of Grodan substrates makes EC steering easier with lower drain volumes.
Irrigation efficiency is a term used to describe how the applied irrigation water is partitioned in the substrate between re-saturation, and refreshment.
Substrates with the highest irrigation efficiency are those which offer maximum EC refreshment with minimal drainage. Irrigation efficiency is an important design feature of modern greenhouse substrates as it allows growers to work with late start and early stop times without the worry of having to “chase” substrate EC. Therefore irrigation strategies can be fine-tuned to the needs of the crop.
The way the applied nutrient solution is partitioned within the substrate and subsequently how WC and EC reacts in NG2.0 substrates can be seen in the day dynamic provided by GroSens system illustrated in figure 1.
Day dynamic of water content and EC showing the diurnal fluctuation in WC & EC
in response to applied irrigation. Grodan NG2.0 substrates have higher irrigation
efficiency as shown by greater EC refreshment compared to other stone wool substrates.
Re-saturation of the slab usually occurs within the first 3-5 irrigation cycles. The exact number will be dependent on the total volume (ml/m2) applied in each session and is characterised by an increase in substrate WC.
When the first effective drainage is realized the substrate WC will stabilize. Subsequent irrigation sessions immediately preceding this event will have maximum effect on decreasing the substrate EC by displacing the old substrate nutrient solution and refreshing it with new irrigated solution. This reaction is clearly visible in the GroSens graphic (Figure 1). Substrates with lower irrigation efficiency partition more of the applied irrigation water into resaturation, effective drainage occurs later and substrate EC will steadily increase day to day, especially with late start and early stop times (Figure 1). This often results in the grower over irrigating the crop to keep EC within acceptable limits.
- If your goal is to level substrate EC the volume of the initial 3-5 irrigation sessions should be 4-6% of your substrate volume (l/m2).
- At light levels >600 W/m2 EC control should be achieved by a combination of higher drain in the middle of the day (11.00 – 14.00 hours) and a lower (reducing on light) irrigation EC.
Towards the end of the day the applied irrigation water will drain easily through the substrate, the majority of this water can be wasted i.e. it has no effect on WC or EC (direct drainage). This is a common occurrence especially if the distance from dripper to drain hole is too short (<20 cm), the capacity of the dripper is too high (4 l/hr) or too many drain holes have been cut.
- For optimum EC management Grodan recommend 1 drain hole per linear 133
cm slab length. This should be cut at the lowest point for more information
please refer to Grodan instruction videos for cutting the drain hole.
- If the drain percentage becomes too high on sunny days after 15:00 hours
irrigate with smaller volumes and adapt the frequency to the radiation sum
At low levels of radiation we can learn to accept higher EC levels in the root zone especially if the plants are too vegetative. However as radiation levels rise >400 W/m2 transpiration is stimulated by a significant increase in leaf temperature. As they rise further (>700 W/m2), cooling of crop becomes more critical. At these moments the plants need more water than feed and the substrate EC should be managed by a reduction in irrigation EC as well as a
targeted irrigation strategy so limiting stress on the plant (Table 1).
Table 1: Acceptable substrate EC levels in relation to expected average daily radiation (W/m2) levels.
| Radiation (W/m2) | EC substrate Tomato | EC substrate Cucumber | EC substrate Pepper |
| 200 | 8,0 | 5,0 | 6,0 |
| 400 | 6,0 | 4,0 | 5,0 |
| 600 | 5,0 | 3,5 | 4,0 |
| 800 | 4,0 | 3,2 | 3,5 |
| 1000 | 3,8 | 3,0 | 3,0 |
The desire to reach an “EC target” will often result in growers over irrigating the crop. Be aware that each time you irrigate the crop will be given a vegetative impulse. Therefore within your irrigation strategy you do not want to be “chasing” substrate EC if you wish to steer in a generative direction on “dark passive” days.
If the crop is described as “too vegetative” steering the root zone to a higher or with an increasing EC and a lower or decreasing WC will provide a generative impulse, especially at light levels below 400 W/m2. Under these circumstances a higher EC level is desirable for controlled growth as more fertilizer will be taken up by the plant. This will result in more dry matter accumulation leading to resilient plants which are less vulnerable to disease.
Continued measuring using the GroSens system in the substrate provides a clear indication of how EC and WC are developing. On hanging gutters capillary substrates (i.e. Grotop Master & Grotop Expert) which exhibit a high level of irrigation efficiency the drain volumes can be reduced depending on light levels to figures outlined in table 2.
| Max radiation W/m2 | Radiation sum J/cm2 | Traditional drain % | Precision Growing drain % |
| 200 | 500 | 20-30% | 5% |
| 400 | 1000 | 10% | |
| 600 | 1500 | 30-60% | 15% |
| 800 | 2000 | 20% | |
| 1000 | 2500 | 25% |
*Assuming measured values for substrate WC & EC in line with those provided in 6 phase reference tables.
*Assuming modern uniform greenhouse and hanging gutters.
Monitoring EC in the slab is an essential part of weekly nutritional monitoring and should be undertaken on a daily basis. Sampling should take place in a number of representative slabs in order for a meaningful and accurate assessment to be made. Sampling is easy, simply push a syringe into the slab and extract a small quantity of nutrient solution (100 ml) and place this into the cup of the EC meter for a direct reading. Calculate the value for delta EC and plot this on a graph this will make it easier to identify trends. Alternatively the slab EC can be monitored directly over the course of the day and the results graphed automatically using GroSens. GroSens also measures and produces a graphical output of the slab water content and slab temperature. GroSens makes EC management easier.
Tips for accurate EC measuring using a portable meter
We are a global leader in the supply of innovative stone wool substrate solutions for the professional horticultural based on Precision Growing principles.
