WATER-RETENTION OF SOFT SILTSTONE FRAGMENTS IN A USTIC TORRIORTHENT, CENTRAL MONTANA

Some soils in the western USA overlie or contain fragments of porous sedimentary rock. Estimations of plant-available water that neglect water retained in the rock may be in error. Using pressure-plate and newly modified tension-table techniques, we measured the water retained at nine water potentials ranging from 0 to -1500 kPa in fissile siltstone fragments from the Cr horizon of a Ustic Torriorthent developed on the Fort Union formation in central Montana. The siltstone fragments held almost-equal-to 0.10 m3 m-3 plant-available water, assuming -1500 kPa (-15 bar) as the lower limit of water availability.