**2.3. Partial root drying system**

Partial rootzone drying (PRD) is a strategy of DI that consists in irrigating only one half of the rootzone in each irrigation event, while the other half is allowed to dry. For this, both halves are watered alternately [40]. This technique was first developed in Australia for vineyards and relies on root-to-leaf signaling induced by a rootzone that is in a drying process [41], decreasing stomatal aperture and leaf growth, preventing water loss [42, 43] with a little effect on photosynthesis, hence increasing transpiration efficiency [41]. At the same time, the wet portion of the root system receiving water enables the plant to maintain a favorable plant water status, such that yield is not significantly compromised and quality may even improve [42]. The PRD performance is based on the assumption that photosynthesis and fruit growth are less sensitive to water deficit than transpiration, and besides, water deficit induces the production of chemical signals, like ABA in the root, that can be translocated to leaves [44] inducing stomatal closure. As demonstrated in a recent meta-analysis, the advantages of PRD in relation to RDI are highly controversial and also depend on the soil texture, a success or enhanced yield performance with RDI and PRDI occurring most likely in deep and finely textured soils [45].
