Definitions & Terms used in Irrigation

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Hydroscopic Water: That water is adsorbed from an atmosphere of water vapour
because of attractive forces in the surface of particles.

Hysteresis: It is the log of in one of the two associated process or phenomena during

Indicator Plant: It is the plant, which reflects specific growing condition by its presence
or character of growth.

Infiltration Rate: It is the maximum rate at which a soil under given condition and at
given time can absorb water when there is no divergent flow at borders

Intake Rate or Infiltration Velocity: It is the rate of water entry into the soil expressed
as a depth of water per unit area applicable or divergence of flow in the soil.

Irrigation Requirement: It refers to the quantity of water, exclusive of precipitation,
required for crop production. This amounts to net irrigation requirement plus other
economically avoidable losses. It is usually expressed in depth for given time.

Leaching: It is removal of soluble material by the passage of water through the soil.

Leaching Requirement: It is the fraction of water entering the soil that must pass
through the root zone in order to prevent soil salinity from exceeding a specific value.

Oasis effect: It is the exchange of heat whereby air over crop is cooled to supply heat for evaporation.

Percolation: It is the down word movement of water through the soil.

Permanent Wilting Point (PWP): Permanent wilting point is the moisture content in
percentage of soil at which nearly all plants wilt and do not recover in a humid dark
chamber unless water is added from an outside source. This is lower limit of available
moisture range for plant growth ceases completely. The force with which moisture is
held by dry soil this point corresponds to 15 atmospheres.

Permeability: Permeability is the property of a porous medium to transmit fluids It is a broad term and can be further specified as hydraulic conductivity and intrinsic

PF: It is the logarithm of height in cm of column of water which represents the total
stress with which water is held by soil.

PH: It is the negative logarithm of hydrogen ion concentration.

Potential Evaporation: It represents evaporation from a large body of free water
surface. It is assumed that, there is no effect of addictive energy .It is primarily a
function of evaporative demand of climate.

Potential Evapo-transpiration: It is the amount of water evaporated in a unit time from
short uniform green crop growing actively and covering an extended surface and never
short of water. Penman prefers the term potential transpiration.

Seepage: It is the water escaped through the soil under gravitational forces.

Agricultural Drainage: It is removal of excess water known as free or gravitational water
from the surface or below the surface of farm land to create favorable condition for
proper growth and development of the plot.

Surface Drainage: when the excess water saturates the pores spaces removal of water
of water by downward flow through the soil is called subsurface drainage.






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