Irrigation Glossary

Effective precipitation Portion of total precipitation which becomes available for plant growth.

Effective rainfall Portion of total rainfall which becomes available for plant growth..

Efficiency

application efficiency
- Ratio of the average depth of the irrigation water stored in the root zone to the average depth of irrigation water applied.
- Ratio of the average depth of irrigation water infiltrated and stored in the root zone to the average depth of irrigation water applied.
- Amount of water stored in the root zone that is available for plant use divided by the average amount of water applied during an irrigation.
- Ratio of the average depth of irrigation water contributing to target, to the average depth of irrigation water applied.
(water) application efficiency of lower half
- Ratio of the average of the lowest one-fourth of measurements of irrigation water infiltrated to the average depth of water applied.
(water) application efficiency of lower quarter
- Ratio of the average low quarter depth of irrigation water infiltrated and stored in the root zone to the average depth of irrigation water applied.
- Ratio of the average of the lowest one-fourth of measurements of irrigation water infiltrated to the average depth of water applied.
best efficiency point Highest efficiency on a pump characteristic curve.
conveyance efficiency Ratio of the water delivered, to the total water diverted or pumped into an open channel or pipeline at the upstream end.
irrigation efficiency Ratio of the average depth of irrigation water that is beneficially used to the average depth of irrigation water applied.
potential application efficiency of Low Quarter low quarter application efficiency obtainable with a given irrigation system when the depth of irrigation water infiltrated in the quarter of the area receiving the least water equals some predetermined value of the soil moisture deficit.
pumping plant efficiency (overall) [Epp] {%} is the ratio of the output power into the water to the input power to the driver.
motor efficiency Ratio of the power delivered to the pump by the power unit to the input power to the motor.
project efficiency Overall efficiency of irrigation water use in a project setting that accounts for all water uses and losses, such as crop ET, environmental control, salinity control, deep percolation, runoff, ditch and canal leakage, phreatophyte use, wetlands use, operational spills, and open water evaporation.
pump efficiency Ratio of the water power produced by the pump, to the power delivered to the pump by the power unit.
(water) storage efficiency Ratio of the amount of water stored in the root zone during irrigation to the amount of water needed to fill the root zone to field capacity.
water use efficiency Ratio of the yield per unit area to the applied irrigation water per unit area.

Effluent irrigation Land application of treated wastewater for irrigation and beneficial use of nutrients.

Electrical conductivity Measure of the ability of the soil water to transfer an electrical charge. Use as an indicator for the estimation of salt concentration.

[ECe] Electrical conductivity of soil water extract.
[ECi] Electrical conductivity of irrigation water.
[ECaw] Electrical conductivity of applied water.

Electrical resistance block Block made up of various materials containing electrical contact wires that is placed in the soil at selected depths to measure soil moisture content (tension). Electrical resistance, as affected by moisture in the block is read with a meter.

Emission point Location where water is discharged from an emitter.

Emission uniformity Index of the uniformity of emitter discharge rates throughout a micro-irrigation system. Takes account of both variations in emitters and variations in the pressure under which the emitters operate.

Emitter Small micro-irrigation dispensing device designed to dissipate pressure and discharge a small uniform flow or trickle of water at a constant discharge, which does not vary significantly because of minor differences in pressure head. Also called a "dripper" or "trickler".

continuous flushing emitter - Micro irrigation system emitter designed to continuously permit passage of large solid particles while operating at a trickle or drip flow, thus reducing filtration requirements.
flushing emitter- Emitter designed to have flushing flow of water to clear the discharge opening every time the system is turned on.
line source emitter - Water is discharged from closely spaced perforations, emitters, or a porous wall along the tubing.
long-path emitter- Emitter which employs a long capillary sized tube or channel to dissipate pressure.
multi-outlet emitter- Device which supplies water to two or more points through small diameter auxiliary tubing.
non-pressure compensating emitter- Emitter designed with a fixed orifice or other components and contains no pressure compensating features.
orifice emitter- Emitter which employs a series of orifices to dissipate pressure.
pressure compensating emitter - Emitter designed to discharge water at a near constant rate over a wide range of lateral line pressures.
vortex emitter -Emitter which employs a vortex effect to dissipate pressure.

Entrance loss {ft, m Energy lost in eddies and friction at the inlet to a conduit or structure.

Evaporation

Water movement from a wet soil or plant surface which does not pass through the plant.
Physical process by which a liquid is transformed to the gaseous state, which in irrigation generally is restricted to the change of water from liquid to vapor. Occurs from plant leaf surface, ground surface, water surface and sprinkler spray.

Evaporation pan

Standard U.S. Weather Bureau Class A pan (48-inch diameter by 10-inch deep) used to estimate the reference crop evapotranspiration rate. Water levels are measured daily in the pan to determine amount of evaporation.
Pan or container placed at or about crop canopy height containing water. Water levels are measured daily in the pan to determine the amount of evaporation.

Evapotranspiration Combination of water transpired from vegetation and evaporated from the soil and plant surfaces.

crop Crop evapotranspiration is the quantitative amount of ET within the cropped area of a field, and which is associated with growing of a crop.Same as plant water requirement.
Amount of water used by the crop in transpiration and building of plant tissue, and that evaporated from adjacent soil or intercepted by plant foliage. It is sometimes referred to as consumptive use.
potential
- Rate at which water, if available, would be removed from soil and plant surfaces.
- Rate at which water, if available, would be removed from the soil and plant surface expressed as the latent heat transfer per unit area or its equivalent depth of water per unit area.
reference
- Rate of evapotranspiration from an extensive surface cool-season green grass cover of uniform height of 12 cm, actively growing, completely shading the ground, and not short of water.
- Upper limit or maximum evapotranspiration that occurs under given climate conditions with a field having a well-watered agricultural crop with an aerodynamically rough surface, such as alfalfa with 50 cm. of top growth.

Exchange capacity [CEC] The sum of exchangeable cations (usually Ca, Ma, K, Na, Al, H) that the soil constituent or other material can adsorb at a specific pH, usually expressed in centimoles of charge per Kg of exchanger (cmol/Kg), or milli equivalents per 100 grams of soil at neutrality (pH = 7.0), meq/100g.

Exchangeable sodium percentage

Fraction of cation exchange capacity of a soil occupied by sodium ions. Exchangeable sodium, (meq/100 gram, spoil) divided by CEC (meq/100 gram soil) times 100. It is unreliable in soil containing soluble sodium silicate minerals or large amounts of sodium chloride.
Percentage of the cation exchange capacity (meq.) of a soil which is occupied by sodium.
Index of the saturation of the soil exchange complex with sodium ions.