What is soil moisture tension?

Answer 1

1.The degree to which water clings to the soil is the most important soil water characteristic to a growing plant. This concept is often expressed as soil moisture tension. Soil moisture tension is negative pressure and commonly expressed in units of bars. During this discussion, when soil moisture tension becomes more negative it will be referred to as "increasing" in value. Thus, as soil moisture tension increases (the soil water pressure becomes more negative), the amount of energy exerted by a plant to remove the water from the soil must also increase. One bar of soil moisture tension is nearly equivalent to -1 atmosphere of pressure (1 atmosphere of pressure is equal to 14.7 pounds per square inch at sea level).

2. A soil that is saturated has a soil moisture tension of about 0.001 bars, or less, which requires little energy for a plant to pull water away from the soil. At field capacity most soils have a soil moisture tension between 0.05 and 0.33 bars. Soils classified as sandy may have field capacity tensions around 0.10 bars, while clayey soil will have field capacity at a tension around 0.33 bars. At field capacity it is relatively easy for a plant to remove water from the soil.

3.The wilting point is reached when the maximum energy exerted by a plant is equal to the tension with which the soil holds the water. For most agronomic crops this is about 15 bars of soil moisture tension. To put this in perspective, the wilting point of some desert plants has been measured between 50 and 60 bars of soil moisture tension.

4.The presence of high amounts of soluble salts in the soil reduces the amount of water available to plants. As salts increase in soil water, the energy expended by a plant to extract water must also increase, even though the soil moisture tension remains the same. In essence, salts decrease the total available water in the soil profile.

Answer 2

Soil moisture tension refers to the force or pressure that the soil exerts on water held within it. It determines how easily water can be extracted by plants from the soil, with higher tension levels indicating less available water for plants to access. Soil moisture tension is an important factor in understanding plant stress and irrigation management.