Soil moisture

• They are dependent on the textures and other characteristics of the soil and must be determined separately for each soil.
• In general, sandy soil drain almost completely at low tension but fine textured clays still hold a considerable amount of moisture.
• A knowledge of the amount of water held by the soil at various tension is required in order to understand the amount of water that can be taken up by the soil before percolation starts and the amount of water that must be used for irrigation.

Soil Moisture Constants

• It is the imaginary boundary of moisture which is available to the plant.
• Following moisture constants are important:

a. Saturation capacity: The saturation capacity is the level of water content when the soil is saturated and all pores are filled with water.

b. Field capacity: Field capacity is the amount of soil moisture or water content held in soil after excess water has drained away.

c. Moisture equivalent: Moisture equivalent is defined as the percentage of water which a soil can retain in opposition to a centrifugal force 1000 times that of gravity.

d. Permanent wilting percentage: The permanent wilting percentage is a range of values of soil water contents over which the removal rate is slow.