pressure bomb or pressure chamber, a device for measuring water potential in plants developed by the American plant scientist Scholander in the 1960s. Since then it has been used for studies in grapevine physiology, and more recently in California as a guide to the timing of vineyard irrigation. The blade of the leaf is placed in an airtight chamber and pressure is increased until xylem fluid exudes from the cut petiole end. However, water potential of the grapevine can vary from hour to hour, depending on sunshine, temperature, humidity and soil moisture content so it is difficult to interpret this dynamic value as an irrigation guide.
