Scheduling irrigation
To schedule irrigation, compare the amount of water available in the crop root zone with the tree’s daily water requirement. If the daily water requirement exceeds the amount of water that can be held in the root zone, irrigate more than once a day. If the soil can hold more than the daily water requirement, irrigate when the available water is depleted. This may be every second or third day, daily or several times a day.
Example
Using the example in Figure 1, on an average day in January in the Upper Swan area these trees would require 62.5 litres of water. The drip-irrigated tree would require two irrigations, one in the morning and another part-way through the day. The sprinkler-irrigated tree would require irrigating every third day.
Rainfall
Rainfall during the irrigation season may reduce the water requirement of your trees. Factor rainfall events greater than 5mm into your irrigation schedule. Not all rain that falls is available to be taken up by your trees. Some is lost to run-off, drainage below the root zone or interception by leaf litter or mulch.
If rain exceeds the amount of water that can be held in the root zone, only consider the amount of water that can be held in the soil since the remainder will be lost to drainage. Keep a close eye on soil moisture during dry winters and in spring as soil can dry out quickly.