A preliminary evaluation of the suitability of sap flow sensors for use in scheduling vineyard irrigation

An experiment was carried out to evaluate the potential for the use of sap flow measurement for scheduling irrigation in vineyards. Sap flow was measured over a 35-day period on 5 different varieties of grape vines (Vitis vinifera), with canopy leaf areas ranging from 3.4 to 16.4 m(2). Irrigation was withheld from some vines to investigate whether sap flow sensors could be used to detect effects of water deficits on transpiration rates. Data obtained from sap flow sensors under well-watered conditions showed differences in transpiration rates caused by differing canopy sizes and changing evaporative demand due to diurnal and daily changes in meteorological conditions. When transpiration rates were expressed on a leaf area basis, mean transpiration from irrigated and non-irrigated vines were initially similar. With time, transpiration from non-irrigated vines became less than that from the irrigated vines. Also differences in diurnal patterns of sap flow became evident, with significantly more sap flow found at night for non-irrigated vines than for irrigated vines. Thus sap flow sensors were able to detect differences in both the timing and amount of water used by irrigated and nonirrigated vines and hence have potential application in irrigation scheduling.