How do I change the slab water content?

How do I change the slab water content?

Changing the slab WC is an important part of the Daily and Season Dynamics for the slab. The daily change from day to night and back to day is an important tool to control the balance of the plant and maintain root heath.

Control over the day level of WC during the season is also important. This is so that the right night drop of WC can be achieved during the winter months when plant activity is low.

Dose Size

The factsheet on dose size shows clearly through the Dose Size Calculator how to calculate the optimal dose size for the volume of stonewool that each dripper is supplying with water and nutrients.The chart from this factsheet below shows clearly the effect of dose size on this distribution.

Through the Dose Size Calculator a recommended dose size is calculated using a dose size factor (DSF). The optimum DSF to give the best distribution throughout the slab is a DSF of 25. So this should be the standard dose size to work on. However we recommend a range of DSF from 20 to 30 which enables you to use the dose size to influence the WC of the slab.

To change the water content levels in the slab the principle is quite straightforward:

  • to increase the WC: put more water in the slab than the plant uses without any drainage;
  • to decrease the WC: put less water in the slab than the plant uses without the EC getting too high.

To increase the WC

In the Daily Dynamics this is in the first period of the day when increasing the WC back up from its night level to day.

In the Season Dynamics this is coming from winter or low light levels to summer or higher light levels. The principle is the same only the time scale is different.

During these periods we can use a DSF of 20 to apply the water so that it spreads sideways more in the slab. For the same amount of water applied in a period, more will stay in the slab with less drain if applied as smaller doses more frequently. This will give less flushing and drain so and it is important to watch that the EC does not build up during this period. If the EC does start to build then a DSF of up to 30 can be used in period 3 in the Daily Dynamics.

It is important that during these critical periods that regular measurements are taken to monitor these changes and to ensure that the target levels are being achieved.

To decrease the WC

In the Daily Dynamics this is period 4 which is the last period from day to night.

This is simply a matter of stopping the watering at the right time to achieve the target night time drop in WC.

In the Season Dynamics this is for maintaining root heath and plant balance when growing into decreasing light levels either at the end of a crop or for summer plantings growing into the winter for production.