Metric potential:(Soil moisture)
• The total water potential that is attributed to the solid colloidal matrix of the soil system
• The energy with which water is held by soil is defined in terms of capillary potential.
• Horizontal flow of water channel is called seepage
. • Water loss from the irrigation channel or canal is mainly due to seepage.
• Down ward movement of water through saturated or nearly saturated soil in response to the gravity.
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• Entry of water from the upper layer of soil is called infiltration.
• It occurs in unsaturated soil.
• Downward movement of nutrients and salts from the root zone with the water is called leaching.
• When all the soil pores are filled with water at a tension of zero “o” bars is termed as saturation 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.
• 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
• The percentage of moisture in root zone at the permanent wilting of plants is called the wilting coefficient or critical moisture point.
• 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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