The British pint is about 20% larger than the American pint since the two systems are not compatible. Almost all other countries have standardized on the metric system, so the size of what may be called a pint varies depending on local custom.
It is usually measured by the depth (in mm) of the water layer that can enter the soil in one hour. An infiltration rate of 15 mm/hour means that a water layer of 15 mm on the soil surface, will take one hour to infiltrate. In dry soil, water infiltrates rapidly.
Perhaps one of the greatest stresses for salt marsh plants to overcome is the difficulty of roots to take up water due to the lowered water potential of salty soil, which averages 10 to 20 ppt, but may exceed 100 ppt in some areas such as salt pans (see below) (Wiegert & Freeman 1990).