There are basically three ways to measure grapevine water status using a pressure chamber, or pressure bomb. These include predawn leaf water potential, midday leaf water potential and stem water potential. Because water status can be measured in three different ways, there has been some confusion about which method is best in a specific situation. This article reviews a recent publication (Williams, L.E. and F.J. Araujo, 2002. Correlations among predawn leaf, midday leaf and midday stem water potential and their correlations with other measures of soil and plant water status in Vitis vinifera. J.Amer.Soc.Hort.Sci. 127(3): 448-454) that outlines the differences in the three and also compares them to other measures of vine water status.
Comparing the three most common methods of measuring vine water status