Crop yield response to water - Cra

BOXDetecting water stress in peachAlthough the established method of detecting tree water stress in peach is the leaf orstem-water potential (Goldhamer et al., 1999), visual indicators may be used to estimatestem-water potential when it is not possible to take actual SWP measurements.In a normal summer day, typical stem-water potential patterns are shown in the figurebelow.FigureDiurnal patterns of stem-water potential for fully irrigated (control) and RDI for peach,Lleida, Spain. In both cases, midday stem-water potential values are the lowest andvalues at predawn (before sunrise) are the least negative, for both well-irrigated andRDI peach trees.Full irrigationRDI0.0- 0.2Stem-water potential (MPa)- 0.4- 0.6- 0.8- 1.0- 1.2- 1.4- 1.6- 1.802:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00Hour at solar timeVisually, it is possible to differentiate a leaf that has a water potential of -0.9 MPafrom one that has a value of -1.9 MPa. The first is fully expanded and usually orientedtowards the sun (Photo D), while the second is partially rolled and droops (Photo A).For the optimal RDI regime that applies stress on Stage II, it is good practise to arriveat midday SWP values close to -1.5 MPa. At that SWP level, some leaf-rolling symptomsmay be observed, but without leaf drop or yellowing, which will indicate excessivewater stress. In the morning, growers should observe expanded leaves. A lead rollingsymptom of water stress in the morning will indicate excessive stress, while nosymptoms at midday will indicate lack of the desired level of stress during Stage II.400crop yield response to water