Movement of water within Soils

• The movement of water within soil controls not only the rate of infiltration but also the rate of supply of moisture to the plant roots.
• Water in the liquid flows through the water filled pore space under the influence of gravity.
• In the films surrounding soil particles, it moves under the influence of surface tension forces.
• Water also diffuses as vapour through the air-filled pore spaces along gradients of decreasing vapour pressure.
• In all cases, the movement is along gradients of decreasing water potential.

Terminologies

Runoff: The portion of total precipitation or irrigation that finds its way into drainage channel.

Infiltration water intake: The movement of irrigation water from the soil surface into and through the soil is called water intake.

Percolation: It is the downward movement of water through saturated or nearly saturated soil in response to the force of gravity. It occurs when water is under pressure or when the tension is smaller than about ½ atmosphere.

Percolation rate: It is synonymous with infiltration rate with the qualitative provision of saturated or near saturated condition.

Infiltration: It is the entry of water from the surface into the soil.

Infiltration rate: Rate of entry of water into the soil and expressed as mm/hr or mm/min or cm/hr.

Infiltration capacity: It refers to the ability of soil to absorb different rate of infiltrations.

Basic or final infiltration: It is the nearly constant rate that develops after sometime has elapsed from the start of irrigation.

Accumulated (Cumulative) infiltration: It is the total quantity of water that enters into the soil in a given time.

Intake rate: It is the rate of infiltration from a furrow into the soil.

Permeability: It is the rate of readiness with which soil transmit water.

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

Interflow: It is the lateral seepage of water in a relatively pervious soil above a less previous layer. Such water usually reappears on the surface of the soil at a lower elevation.