Water potential is the most fundamental and essential measurement in soil physics because it describes the force that drives water movement. As one soil physicist put it, “Measuring water potential in soils is like measuring voltage in electronics.”
It is a difficult measurement to make. Still, anyone determined to understand the soil-plant-atmosphere continuum must discover how to make good water potential measurements. As that soil physicist said, “Imagine telling an electrical engineer that he has to work and design without knowing the voltage, that you’re going to take all his voltmeters away. It would be impossible to do the research, impossible to advance. No matter how difficult that measurement is to make, we have to make it.”
Making good water potential measurements is largely a function of choosing the right instrument and using it skillfully. In an ideal world, there would be one instrument that simply and accurately measured water potential over its entire range from wet to dry. In the real world, there is an assortment of instruments, each with its unique personality. Each has its quirks, advantages and disadvantages. Each has a well-defined range. Nearly every one can frustrate the novice user.