<P> In contrast, atmospheric water potentials are much more negative--a typical value for dry air is − 100 MPa, though this value depends on the temperature and the humidity . Root water potential must be more negative than the soil, and the stem water potential and intermediate lower value than the roots but higher than the leaf water potential, to create a passive flow of water from the soil to the roots, up the stem, to the leaves and then into the atmosphere . </P> <P> A tensiometer, electrical resistance gypsum block, neutron probes, or time - domain reflectometry (TDR) can be used to determine soil water potential energy . Tensiometers are limited to 0 to − 85 kPa, electrical resistance blocks is limited to − 90 to − 1500 kPa, neutron probes is limited to 0 to − 1500 kPa, and TDR is limited to 0 to − 10,000 kPa . A scale can be used to estimate water weight (percentage composition) if special equipment is not on hand . </P>

What is the role of water potential in the movement of water