Root zone capacity
The amount of water that can be held in the root zone varies with the type of irrigation system used, soil type, depth of the effective root zone and proportion of stone or gravel in the soil.
Figure 1 shows two trees of the same size (9 square metre canopy area), growing in a hedgerow in a loam soil. The root zone of both trees is 30cm deep. One tree is irrigated with two drippers, the other with a fully overlapping micro-sprinkler system. The soil within the wetted root zone of the tree with the two drippers can hold 34 litres of Readily Available Water, much less than the comparable sprinkler-irrigated tree where the root zone can hold 189 litres.
Figure 1 Example of water-holding capacity under different irrigation systems