The percentages of OM in the biomass samples were found by the amount of ash at 850[degrees]C  and hygroscopic water
, and for the oil shales by ash of the acid-treated samples counting the contributions of hygroscopic water
Descriptive terms for soil water content are saturation, gravitational water, field capacity, plant available water, capillary water, plant unavailable water, and hygroscopic water.
Capillary water is the water content at field capacity minus the water content in air-dry soil, or hygroscopic water content.
Hygroscopic water, as it is called, is held to particles so tightly, between -31 and -10,000 bars, that it can only be removed by drying soil in an oven.
Hygroscopic water is too tightly held by adhesion to be used by plants.