Nocturnal heat-pulse sap flow as a sensitive system to assess drought effects on grapevines : an irrigation scheduling application?

The compensated heat-pulse method, New Zealand (cHP) was tested on grapevines (Vitis vinifera L. cv. Shiraz) under a PRD trial in Benalla, Victoria (season 2003-2004). Results showed that vines (all treatments) where in constant stress during the season and PRD treatments were able to maintain an almost constant transpiration rate, independently of atmospheric demand, which could indicate a better stomatal control. Other whole-tree water status monitoring methods were midday stem water potential (s) and infrared thermography (IR). The cHP offered a continuous and sensitive physiological technique to monitor the effect of watering at very low transpiration rates. Therefore, the sensors used were able to register night time sap flow (SN), which was more evident after irrigations and decreased gradually over time until the next irrigation. SN was significantly correlated to s obtained from the day before. Monitoring SN could be a suitable method to assess grapevine water status and the capacity of vines to recover from the daily water stress. We propose SN as a possible irrigation scheduling technique.