A relatively quick way to measure the water potential in large pieces of crop tissues, such as leaves and stems, is to use a pressure chamber/bomb. This technique assumes that the water pressure within vasculum is close to the average pressure potential of the entire organ because in most cases the osmotic pressure of the vasculum is low. According to Stegman31, a pressure bomb measures the compressive or expansive potential of the vasculum. However, because the osmotic potential of the vascular juice is usually insignificant compared to the compressive potential, the negative pressure value in the pressure chamber is often taken as the potential of the entire leaf. The pressure bomb is made of a hollow chamber to accomodiate the leaf specimen. The leaf specimen is used through a gasket to hold the petiole. There is also a pressure capsule that draws compressed air into the chamber. On the other hand, the same chamber is also connected to a barometer. The leaf is placed into the chamber in a way that the petiole remains outside, and as the valve of the compressed air capsule opens, the pressure inside the chamber gradually increases. The leaf wrinkles (wilts) and reaches a pressure point where a drop comes out of the petiole. Just when the first drop comes out of the petiole, the pressure is read on the machine.

The procedure was that in the afternoon, when the LWP reached its lowest (2–3 p.m. local time), the leaf samples, which were completely exposed to sunlight, were selected from each treatment plot (three replications). After each leaf sample was selected, it was cut by a sharp blade cutter and immediately put into the apparatus and the pressure in the chamber was increased by opening the gas valve. As the pressure in the chamber was increased by a handheld magnifying glass, the cut end of the leaf lamina remaining outside the device was carefully observed. This procedure was repeated for other samples and the mean LWP was obtained for three plots in each treatment.

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