The percent water is then expressed as a percent on a dry weight basis. This means that 1 cm 3 of soil will store 0.18 cm 3 of water, or that soil 1 cm deep will store 0.18 cm of water. 6.2 Tensiometers Devices designed to measure soil moisture tensions directly. Restricted to matric potentials in the range of 0 to -1 bar. As water is pulled out of the porous ceramic cup in response to the matric potential of the soil, water pulls on the vacuum gauge changing the reading.
Tensiometers fail when air bubbles develop in the water column.
6.3 Resistance Blocks Consists of two electrodes embedded in a porous block. 6.4 Neutron moisture meter Device that emits high energy fast neutrons into the soil. These neutrons collide with water molecules and result in lower energy slowed electrons. When the pressure is increased to a certain value, all water held at energies less than that value will be forced through the porous plate into the lower chamber and quantified by a loss of mass or volume. Since the stomates are closed gas exchange is not possible and therefore photosynthesis ceases.