The term soil moisture regime refers to the presence or absence either of ground water or of water held at a tension of less than 1500 kPa, in the soil or in specific horizons, by periods of the year. Water held at a tension of 1500 kPa or more is not available to keep most mesophytic plants alive. The availability of water is also affected by dissolved salts. But if a soil is saturated with water that is too salty to be available to most plants, we call such a soil salty rather than dry. Consequently, a horizon is considered dry when the moisture tension is 1500 kPa or more, and is considered moist if water is held at a tension of less than 1500 kPa but more than zero. A soil may be continuously moist in some or all horizons either throughout the year or for some part of the year. It may be either moist in winter and dry in summer, or the reverse. In the northern hemisphere, summer refers to the months of June, July, and August, and winter means December, January, and February.

7/15/98