The positioning of the drainage slits in combination with the right irrigation dose size influences directly the distribution of water and EC in the slab to produce the minimum variation of water content and EC laterally and vertically in the slab. This is a job that has to be done only once but will influence the slab for the rest of the season, so it is very important that it is done correctly.

Additional drainage slits should never be made in the slab at a later date as they will change the drainage pattern in the slab which may be detrimental to the roots in some areas of the slab.

Ideally there should be the same number of drippers in every cube with no extra drippers put directly into the slab.

Additional tips for making the drainage slits:

• make drainage slits at both ends of the slabs at the lowest points;
• make additional drainage slits exactly between the cubes. This creates the same “cone” or drainage pattern for every dripper reducing the standard deviation of EC and more efficient flushing and water efficiency;
• this can also be done on both sides of the slab on hanging gutters to make sure that all the slabs drain evenly when the gutters are not quite level;
• make sure that all the drainage slits are right to the bottom of the slab and are wide enough to prevent the roots slowing down the drain water (3 to 4 cm);
• drain the slabs 24 hours before planting;
• do not make additional drainage slits during the crop as this will change the drainage pattern in the slab and can cause root death;
• never make a drainage slit under a dripper as this can give “false drain”.

Yes it is. The main goal is to stay in a safe range. If you go too low, you will face problems in growth and risk damaging the roots. When you go too high some nutrients will be harder to take up by the plant. Keep the pH above 5.2.

In the Season Dynamics (Smart Root Zone Management App) we state that it is important to have a target EC for each of the different periods during the crop.

To control the EC to the target levels it is important to use the proper measuring strategy so that you can make small and frequent changes to your irrigation strategy. It is always easier and safer to make frequent small changes than to make big changes when the EC has got too high.

The important factors for good EC control are:

• good initial root distribution after planting (first 6 to 8 weeks);
• the correct dose size per dripper;
• correct use of the Daily Dynamics (Smart Root Zone Management App).

Period 1 in the Daily Dynamics is very important to re-fill the slabs as evenly as possible with the correct dose size. This will not only give better EC control later in the day but also reduce the variation in EC around the glasshouse.

To reduce EC it is necessary to flush the slab more. This can be done by:

• increasing the frequency (by light or time);
• increasing the dose size (within the recommended range).

Other points of attention:

• So look for a higher percentage of drain especially in period 2 and period 3 of the Daily Dynamics.
• Take care if reducing the drip EC that the Delta EC does not get too big (>3).

Mistakes happen and sometimes the slab can dry out with insufficient water especially the top of the slab.

To re-wet the slab it is best to use small and frequent waterings. This will help keep the water you apply in the slab and at the top. Large dose will push the water to the bottom of the slab and quicker to the drain point.

So it is important to use a dose size factor of 20 or lower if possible within the limitations of your system.

It is also important that you apply more water than the plant is using, so watering at night or before plant activity in the morning is a good time for this but take care of the Delta EC to avoid problems with fruit splitting (tomatoes) etc.

The spacing of the dippers has a big effect on the even distribution of water and nutrients in the slab. The flow of this water is spread evenly by the stone wool to refresh the nutrient solution around the roots. This is what we call the Cone. The Cone starts in the cube and spreads down and sideways.

The cube will increase the width of the cone and the volume refreshed by the dripper giving more efficient water and fertilizer use. This is vital to give good refreshment and even water content, EC control and minimizing drain.

When changing plant density or crop there can be more drippers than cubes to put them in. In this case:

• check if you can remove or block off these drippers and still have enough irrigation capacity;
• if not try and put the same number off drippers into every slab;
• make sure that you do not put the dripper above a drainage slit;
• try and put the extra dripper at the high end of the slab;
• take care when measuring with a hand meter that you do not measure too close to this dripper as the EC level will be closer to the drip EC;
• make sure that this extra dripper is not giving you “false drainage”.

The optimal dose size for our slabs can be calculated using the Dose size Calculator or manually as below.

Example:

Slab with volume = 100 x 15 x 7.5 cm = 11.25 liter
3 cubes volume = 3 x (10 x 10 x 6.5 cm) = 3 x 0.65 liter = 1.95 liter

Total stone wool volume = 13.2 liter

Dose size:

• 3 drippers / slab = 13.2 / 3 = 4.4 liter / dripper
• Dose size = 25 x 4.4 = 110 cc

This is the total volume of substrate (cube and slab) supplied per dripper multiplied by the DSF (Dose Size Factor). So the larger the volume of substrate per dripper the larger the dose size.