Soil Water

Abstract

Abstract Although water in saturated media is free to drain into openings such as wells, soil water is normally bound to soil surface by attractive forces and only freely drains into openings when the fluid pressure is positive. When soil water pressures are negative, water only partially fills soil pores—the remaining voids are filled with air or soil gasses. The negative water pressure is referred to as the soil tension. Water contents vary from very low values when the soil is dry and the soil tensions are large to saturated values when the soils are wet and the soil tensions are small. The negative pressure, or soil tension, and water contents of soils can be determined with a variety of field techniques, including tensiometers, time‐domain reflectometers, and psychrometers. The relationship between soil tensions and water contents is called the moisture characteristic curve, which is normally determined in a laboratory. Soil water samples can be collected with lysimeters.