Period 3

Objective

• To maintain the target water content and achieve drain on every round of 25 to 30% or to achieve the target slab EC.
• Especially during periods of high temperature and high VPD or low humidity the plant tends to use more water and less salts during this period.
• The EC build up is therefore higher so more drain is required to hold the EC level.
   

Start time

• Period 3 will start at the end of Period 2 (midday).
• If the start time and stop time during the day are related to sunrise and sunset, period 2 and 3 will increase naturally in length as the day length increases.
   

Length of period

• As this is the last true watering period of the day the stop time will be depend on the target night time water content drop and the volume of the substrate.
• As a guide figure 4 to 5 hours before sunset (or later in hot climates).
   

Dose size

• A dose size factor 25 as a base figure with perhaps up to dose size factor 30 in high light intensities or if trying to reduce EC.
   

Time starts

• Time induced starts also are necessary to avoid a build up of EC in dull weather.
• The time between time starts is dependant on slab volume etc.
• Guide 15 to 60 minutes.
   

Light starts

• To achieve a higher drain percentage during this period the irrigation needs to be more frequent so a higher mls/joule figure will be needed (or a larger dose size).
• These have to related to crop and conditions but in general for most crops in Northern Europe 2.5 to 3.2 mls/joule/m² (see Dose Size Calculator). In extreme climates this may be a higher figure.
• Click here for more information on light influenced starts.
   

Other factors

• EC levels in the slab can build up very quickly during this period so it is very important to achieve the target drain especially in low volumes of substrate.
• The end time of this period also needs to be looked at in association with any pre-night on temperature being used. Watering during the pre-night temperature period will increase root pressure.