Soil Moisture Constants

Metric potential:(Soil moisture)

• The total water potential that is attributed to the solid colloidal matrix of the soil system

Capillary potential:

• The energy with which water is held by soil is defined in terms of capillary potential.

Seepage:

• Horizontal flow of water channel is called seepage

. • Water loss from the irrigation channel or canal is mainly due to seepage.

Percolation:

• Down ward movement of water through saturated or nearly saturated soil in response to the gravity.

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Infiltration:

• Entry of water from the upper layer of soil is called infiltration.

• It occurs in unsaturated soil.

Leaching:

• Downward movement of nutrients and salts from the root zone with the water is called leaching.

Saturation capacity:

• When all the soil pores are filled with water at a tension of zero “o” bars is termed as saturation capacity.

Field capacity:

• The soil moisture content after 2-3 days of irrigation and after drainage of gravitational water has become very slow and soil moisture content had become relatively stable.

• At the field capacity, the large pores filled with air and the micro pores are filled with water.

• It is considered as the upper limit of water availability to plants.

• The tension at field capacity ranges from -0.1 to —0.33(1/3)

• It is determined with the help of pressure plate apparatus.

PWP:

• The concept permanent wilting point (PWP) proposed by Briggs and Shantz in 1912.

• They utilized dwarf sunflower as an indicator plant.

• Soil moisture content at which plants can be no longer obtains enough moisture to meet their requirement and remained unless water is added to the soil.

• It is the lower limit of available water to plant.

• Although plants not dead, but they are now in a permanently wilted condition and die if water is not added.

• Soil moisture tension is -15 bars

Wilting coefficient:

• The percentage of moisture in root zone at the permanent wilting of plants is called the wilting coefficient or critical moisture point.

Available water:

• Concept of available water given by Veihmayer and Hendrickson 1981

• It is the portion of capillary water held between Field Capacity to PWP (i.e. – 0.3 to -15 bars).

Ultimate wilting point:

• The moisture content at which wilting is complete and the plant die is called UWP.

• At UWP the soil moisture tension is as high as -60 bars.

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