Sap flow measurements in grapevines (Vitis vinifera L.) - 2. Granier measurements

The Granier-system, a relatively simple and continuous method for measuring sap flux density, has been adapted and evaluated for its use in older, mat ure grapevines. The original calibration of Granier (1985, Annales Sciences Forestieres, 42, 193-200) could be extended to a sap flux density of up to 400 10(-6) m(3) m(-2) s(-1) with only little error at high flux densities. A time lag of around 20 min was apparent between transpiration and calcula ted sap flow which was attributed to the thermal mass of the sensors themse lves. The time lag and the consequently dampened response of the system cau sed a very low accuracy over short time periods thus reducing the value for detailed plant physiological investigations. However, when integrating ove r longer time intervals, much of the error cancelled out. For daily values the maximum error was within +/- 10% and after a period of 89 days only 1.5 % error remained. This method is thus best suited for long term measurement s of total water use.