Some terminologies

a) Wilting range: It is the range of soil moisture from permanent wilting point and ultimate wilting point.

b) Readily available Water: The difference in moisture content of soil between field capacity and the permanent wilting point is called available soil moisture. But, only a portion of available water which is most easily extracted by plants is called readily available water. Around 75-80% of the available water is the readily available water.

c) Soil moisture deficiency: The water required to bring the soil moisture content of a given soil to its field capacity is called field moisture deficiency or soil moisture deficiency.

d) Equivalent moisture: As the field capacity is the water retained by saturated soil after being acted upon by gravity. Similarly, equivalent moisture is the water retained by a saturated soil after being centrifuged for 30 minutes by a centrifugal force of 1000 times that of gravity. Therefore, it is slightly less (for sandy) or at the most equal to field capacity.

e) Infiltration: When water falls on a given formation, a small part of it is first of all absorbed by the top thin layer of soil, so as to replenish the soil moisture deficiency and gradually more downward after filling pores. So, the process whereby the water enters the earth surface strata of the soil, and moves downwards is known as infiltration.

f) Percolation: It is the downward movement of the water through saturated or nearly saturated soils in response to the force of gravity.

g) Seepage: It is the infiltration (vertically) downward and lateral movement of water into the soil or substrata from a source of supply such as reservoir or irrigation canal.