• Abbreviation for alternating current.

AC pipe

  • Asbestos-cement pipe was commonly used for buried pipelines.  It combines strength with light weight and is immune to rust and corrosion. (James, 1988) (No longer made.)


  • Substance with a pH less than 7.0


  • Physical attraction of unlike substances to one another. In soils, it is the process that holds water molecules tightly to soil solids at the soil-water interfaces.

Adjusted sodium adsorption ratio

  • Index of permeability problems, based upon water quality.


  • Concentration of a substance at the surface of another, more noticeable with substances of large surface area, such as clay particles.

Advance Ratio

  • Ratio of the time for the water to reach the end of the field to the total set time for an irrigation set on a furrow irrigation system.  The ratio should be less than 0.5 to have a good distribution uniformity.

Advance time

  • Time required for a given stream of irrigation water to move from the upper end of a field to the lower end.
  • Time required for a given surface irrigation stream to move from one point in the field to another.


  • To supply with air.

Aeration capacity

  • Volume fraction of air filled pores in a soil at field capacity.


  • Group of primary soil particles that cohere to each other stronger than to other surrounding particles. 
  • Groups of individual soil particles, held together naturally and consisting of particles of sand, silt and clay separated from each other by pores, cracks or planes of weakness.  The term, soil structure, refers to this arrangement of the soil in natural aggregates. Various types of soil structure are recognized (Massive, platy, prismatic, blocky, granular).

Alfalfa valve

  • Outlet valve attached to the top of a pipeline riser with an opening equal in diameter to the inside diameter of the riser pipe and an adjustable lid or cover to control water flow... 


  • Substance that will kill or control algae growth.

Alkaline (alkali) soils

  • Soil with pH greater than 7.0.
  • Soil with an exchangeable sodium percentage greater than 15%.

Allowable depletion

  • That part of soil moisture stored in the plant root zone managed for use by plants, usually expressed as equivalent depth of water in acre inches per acre, or inches.

Allowable voltage loss

  • Voltage loss in a circuit or portion of a circuit which, if not exceeded, will result in the electrical device working correctly.

Alternating current [AC]

  • Current in which the flow of electrons in a circuit flow in one direction and then in the reverse direction.


  • Unit of electrical current.  The unit is used to specify the movement of electrical charge per unit time through a conductor.



  • Negatively charged ion, which during electrolysis is attracted towards the anode.  The most common anions in soil extracts and waters are bicarbonate, sulphate, carbonate, chloride and nitrate ions.


  • Underground geological formation, or group of formations, containing usable amounts of groundwater that can supply wells or springs for domestic, industrial, and irrigation uses. Removing more groundwater from an aquifer than is naturally replenished is called overdrafting, and can result in a dropping water table, increased pumping costs, land subsidence (which reduces the future recharge capacity), saltwater intrusion, reduced streamflows in interconnected ground- and surface-water systems, and exhaustion of groundwater reserves.


  • Portion of a full circle (360) covered by a part circle sprinkler.


  • Surface included within a set of lines (Webster). In irrigation, usually used to describe a surface of land or cross section of pipe.

Atmospheric pressure

  • Absolute pressure measured at any location. Standard pressure at sea level is defined as 14.7 psi or 34.0 ft of water.

Available soil moisture

  • The difference between the actual soil moisture content in the root zone soil and the wilting point.

Available water

  • Portion of water in a soil that can be readily absorbed by plant roots. It is the amount of water released between in situ field capacity and the permanent wilting point.


Back flow

  • Any unwanted flow of used or non-potable water or substance from any domestic, industrial or institutional piping system into the pure, potable water distribution system. The direction of flow under these conditions is in the reverse direction from that intended by the system and normally assumed by the owner of the system.

Backflow prevention device [BPD]

  • Safety device which prevents the flow of water from the water distribution system back to the water source

Back pressure

  • Increase of pressure in the downstream piping system above the supply pressure at the point of consideration that would cause, or tend to cause, a reversal of the normal direction of flow.

Back siphonage

  • Reversal of flow (backflow) due to a reduction in system pressure that causes a negative or sub-atmospheric pressure to exist at a site in the water system. 


Best management practice

  • BMP is a voluntary irrigation practice that is both economical and practical and is designed to reduce water consumption and protect water quality while maintaining a healthy, functional landscape. (John Ossa, Committee Chair, IA Water Management Committee. Nov. 2000)


  • Water emission device that tends to bubble water directly to the ground or that throw water a short distance, on the order of one foot, before water contacts the ground surface.

Bulk density of soil

  • Mass of dry soil per unit bulk volume ...

Bulk density of water

  • Same as density of water. Mass of water per unit bulk volume. 


Capillary water

  • Water held in the capillary, or small pores of the soil, usually with soil water pressure (tension) greater than 1/3 bar. Capillary water can move in any direction.


  • Application of chemicals (including fertilizers) to crops through an irrigation system by mixing them with the irrigation water.

Class (pipe)

  • Term generally used to describe the pressure rating of SDR-PR (standard dimension ratio-pressure rated) PVC pipe. For example, a class 200 pipe has a pressure rating of 200 psi. (colloquial)
  • Term used to identify the physical characteristics of thermoplastic pipe.

Class, soil

  • Group of soils defined as having a specific range in one or more particular properties such as acidity, degree of slope, texture, structure, land- use capability, degree of erosion, or drainage.


  • -- Naturally occurring material composed primarily of fine-grained minerals, which is generally plastic at appropriate water contents and will harden when dried or fired. ... 


  • Arid Climate - Characterized by low rainfall and high evaporation potential. A region is usually considered as arid when precipitation averages less than 10 inches per year.
  • Humid Climate - Characterized by high rainfall and low evaporation potential. A region generally is considered as humid when precipitation averages more than 40 inches per year.
  • Semiarid Climate - Characterized as neither entirely arid nor humid, but intermediate between the two conditions. A region is usually considered as semiarid when precipitation averages between 10 and 20 inches per year.
  • Subhumid Climate - Characterized by moderate rainfall and moderate to high evaporation potential. A region is usually considered subhumid when precipitation averages more than 20 inches per year, but less than 40 inches per year.


  • Allowable stress factor Used to modify reference evapotranspiration to reflect the water use of a particular plant or group of plants particularly with reference to the water stress. Ratio of the actual crop evapotranspiration to it potential (or reference) evapotranspiration.
  • Crop Coefficient - used to modify reference evapotranspiration  to reflect the water use of a particular plant or group of plants particularly with reference to the plant species.
  • Density Factor - Used to modify reference evapotranspiration  to reflect the water use of a particular plant or group of plants particularly with reference to the density of the plant material. 
  • Landscape Coefficient - Used to modify reference ET which includes species factor, density factor and microclimate factor.

Coefficient, consumptive use

  • Ratio of volume of irrigation water consumptively used to the total volume of irrigation water that has left the region, both in a specified period of time.

Coefficient of runoff

  • Runoff coefficient used in the rational method of predicting a design peak runoff rate. It helps to characterize runoff rate from a watershed area.


  • Attraction of water molecules to each other.
  • Bonding strength between soil particles.

Continuous-flow irrigation

  • System of irrigation water delivery where each irrigator receives the allotted quantity of water continuously.

Control structure

  • Water regulating structure, usually for open channel flow conditions


  • An electric timing device that operates each (irrigation) zone for a predetermined time and frequency.
  • An automatic timing device that sends an electric signal for automatic valves to open or close according to a set irrigation schedule

Conveyance loss

  • Loss of water from a channel or pipe during transport, including losses due to seepage, leakage, evaporation, and transpiration by plants growing in or near the channel. 

Coupler (sprinkler)

  • Device, either self-sealed or mechanically sealed, that connects the ends of two lengths of pipe or pipe to a hose.

Cross connection

  • Any actual or potential connection or structural arrangement between a public or private potable water system and any other source or system through which it is possible to introduce into any part of the potable system any used water, industrial fluids, gas, or substance other than the intended potable water with which the potable system is supplied. By-pass arrangements, jumper connections, removable sections, swivel or change-over arrangements or other "temporary" arrangements through which backflow could occur are considered to be cross-connections. 

Crop growth stages

  • Periods of like plant function during the growing season. Usually four or more periods are identified 
  • Initial - Between planting or when growth begins and approximately 10 percent ground cover.
  • Crop Development - Between about 10 percent ground cover and 70 or 80 percent ground cover.
  • Mid Season - From 70 or 80 percent ground cover to beginning of maturity.
  • Late - From beginning of maturity to harvest.

Cumulative intake

  • Depth of water absorbed by soil from the time of initial water application to the specified elapsed time.


  • Movement or flow of electrons.
  • The flow of electrons in a conductor.)

Cycle time

  • Length of water application periods.


Deep percolation

  • Movement of water downward through the soil profile below the root zone that cannot be used by plants.

Deficit irrigation

  • Irrigation water management alternative where the soil in the plant root zone is not refilled to field capacity in all or part of the field.

Deep percolation percentage

  • Ratio of the average depth of irrigation water infiltrated and drained out of the root zone to the average depth of irrigation water applied.

Degree of hazard

  • The type of backflow preventer used to prevent backflow from occurring at the point of a cross-connection depends on the type of substance which may flow into the potable water supply. A pollutant is considered to be any substance which would affect the color or odor of the water, but would not pose a health hazard. This is also considered a non-health hazard. A substance is considered a health hazard if it causes illness or death if ingested. This health hazard is called a contaminant.

Demand Irrigation

  • Procedure where each irrigator may request irrigation water in the amount needed and at the time desired.


  • Mass of water per unit volume. Same as bulk density of water.


  • Pattern of dots that shows the expected coverage from a particular combination of sprinklers, nozzles, pressure and spacing.
  • Graphical representation of precipitation rates.


  • General term relating to depth of soil, water, or similar.

Depth of irrigation

  • Depth of water applied
  • Depth of soil affected by watering


  • Dimension / size of a circular pipe, usually but not always the inside diameter

Diameter of throw

  • Average diameter of the area wetted by an irrigation sprinkler operating in still air.

Dielectric union

  • Pipe connection (union) having an insulator between the two sides of the union for the purpose of reducing corrosion caused by galvanic action.

Dimension ratio

  • Ratio of the average pipe diameter to the minimum wall thickness. The pipe diameter may be either outside or inside diameter.

Direct current

  • Current in which electrons flow constantly in one direction.

Distribution system

  • System of ditches, or conduits and their controls, which conveys water from the supply canal to the farm points of delivery.

Distribution uniformity

  • Measure of the uniformity of irrigation water over an area.

Distribution uniformity of lower quarter

  • Ratio of the average low quarter depth of irrigation water infiltrated to the average depth of irrigation water infiltrated.
  • -- Ratio of the average of the lowest one-fourth of measurements of irrigation water infiltrated (or applied) to the average depth of (the total) irrigation water infiltrated (applied).


  • Period of dryness especially when prolonged that causes extensive damage to crops or prevents their successful growth.

Dry weight

  • Oven dry weight of a soil sample.

Ductile iron

  • Form of iron used to make pipe and fittings.

dynamic pressure

  • Measure of water pressure with the water in motion (also known as working pressure). Measured in PSI in North America and BAR in Europe.


Effective precipitation

  • Portion of total precipitation that is available for plant growth.

Effective rainfall

  • Portion of total rainfall that is available for plant growth.


  • Efficiency of the watering application
  • 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.
  • Ratio of the average of the lowest one-fourth of measurements of irrigation water infiltrated to the average depth of water applied.
  • 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.
  • Electrical conductivity of soil water extract. Electrical conductivity of irrigation water. Electrical conductivity of applied water.

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.


  • 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 - 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 - 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 - Designed to discharge water at a near constant rate over a wide range of lateral line pressures.
  • Vortex Emitter - Which employs a vortex effect to dissipate pressure.

Entrance loss

  • Energy lost in eddies and friction at the inlet to a conduit or structure.


  • 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.



  • Application of nutrients through an irrigation system.


  • Acronym for female iron pipe thread.

Flow rate

  • Rate of flow or volume per unit period of time.

Frequency distribution

  • Values in a sample are grouped into a limited number of classes. A table is made showing the class boundaries and the frequencies (number of members of the sample) in each class. The purpose is to show a compact summary of the data.  
  • Measurement and presentation of various fractions of total water applied for selected depth ranges referenced to average depth applied.


  • Soil consistency term referring to the ease with which the soil aggregates may be crumbled (in the hand), i.e. a friable soil is easily crumbled in the hand.

Friction loss

  • Also referred to as pressure loss.
  • As water moves through an irrigation system, pressure is lost because of turbulence created by the moving water. This turbulence can be created in pipes, valves or fittings. These losses are referred to as friction losses.

Frost protection

  • Applying irrigation water to affect air temperature, humidity, and dew point to protect plant tissue from freezing. The primary source of heat (called heat of fusion) occurs when water turns to ice, thus protecting sensitive plant tissue.

Full irrigation

  • Management of water applications to fully replace water used by plants over an entire field.


  • Chemical pesticide that kills fungi or prevents them from causing diseases on plants.


  • Small channel for conveying irrigation water down slope across the field. Sometimes referred to as a rill or corrugation.
  • Trench or channel in the soil made by a tillage tool.


Gravitational water

  • Soil water that moves into, through, or out of the soil under the influence of gravity.


  • Acceleration caused by the attraction of the mass of earth to bodies at or near its surface.

Ground water

  • Water occurring in the zone of saturation in an aquifer or soil.

Growing season

  • Period, often the frost-free period, during which the climate is such that crops can be produced.


Head ditch

  • Ditch across the upper end of a field used for distributing water in surface irrigation.

Head gate

  • Water control structure at the entrance to a conduit or canal.

head to head spacing

  • Spacing of sprinkler heads so that each sprinkler throws water to the adjacent sprinkler.


  • Linear dimension used to describe the vertical distance from a point to a datum.


  • Chemical substance designed to kill or inhibit the growth of plants, especially weeds.

High density polyethylene [HDPE]

  • One of several forms of polyethylene used to make pipe and other irrigation components.

Horizon (soil)

  • Layer of soil or soil material approximately parallel to the land surface and differing from adjacent genetically related layers in physical, chemical, and biological properties or characteristics such as color, structure, texture, consistency, kinds and number of organisms present, degree of acidity or alkalinity, etc.


  • Water Horsepower - Energy added to water by a pump.
  • Input Horsepower - Energy added to a motor or engine
  • Brake Horsepower - Power required to drive a pump.  

Hose bib

  • Valve configured to be mounted on a wall having threads to accommodate the connection of a water hose.


  • Outlet, usually portable, used for connecting surface irrigation pipe to an alfalfa valve outlet. (NRCS, 1997)

Hydraulic conductivity

  • Coefficient describing the ease at which the soil pores permit water movement. (NRCS, 1990)
  • Soil-water characteristic describing the ability of water to flow through a particular soil.


  • Grouping of plants with similar water requirements so that they can be irrigated with a common zone. (Weinberg and Roberts, 1988)

Hygroscopic water

  • Water that is tightly held by soil particles.  It does not move with the influence of capillary action or gravity, and it is normally unavailable to plants. 



  • Abbreviation for inside diameter (usually of a pipe).


  • Process of water movement through the soil surface into the soil matrix.

Infiltration rate (intake rate.)

  • Downward flow of water into the soil at the air-soil interface. 
  • How quickly water moves into the soil


  • Device used to measure the infiltration rate / intake rate of water into soil.

Inrush current

  • Current necessary to initially open the solenoid valve.

Intake family

  • Grouping of intake characteristics into families based on field infiltrometer tests on many soils.  

Intake, initial

  • Depth (rate) of water absorbed by a soil during the period of rapid or comparatively rapid intake following initial application.

Intake rate

  • Rate that (irrigation) water enters the soil at the surface.

Intake rate

  • Rate at which water percolates into the soil after infiltration has decreased to a low and nearly constant value.


  • Part of precipitation or sprinkler irrigation system applied water caught on the vegetation and prevented from reaching the soil surface.

Internal manual bleed

  • Feature which allows an automatic valve to be opened manually (without controller) by releasing water from above the diaphragm to the downstream side of the valve. Useful during installation, system start-up and maintenance operations when it is undesirable for water to escape into the valve box.

Inverted siphon

  • Closed conduit (for conveying water) with end sections above the middle section; used for crossing under a depression, under a highway or other obstruction. Sometimes called a sag pipe.

Irrecoverable water loss

  • Water loss that becomes unavailable for reuse through evaporation, phreatophytic transpiration, or ground-water recharge that is not economically recoverable.

Irrigable area

  • Area capable of being irrigated, principally based on availability of water, suitable soils, and topography of land.


  • Intentional application of water to the soil, usually for the purpose of crop production (reclaiming soils, temperature modification, improving crop quality).  
  • Intentional application of water for purposes of sustained plant growth and/or optimized production.


  • gross Water actually applied, which may or may not be total irrigation water requirement; i.e. leaving storage in the soil for anticipated rainfall, harvest. (NRCS, 1997)
  • net Actual amount of applied irrigation water stored in the soil for plant use or moved through the soil for leaching salts. Also includes water applied for crop quality and temperature modification; i.e. frost control, cooling plant foliage and fruit. Application losses, such as evaporation, runoff, and deep percolation, are not included.

Irrigation audit

  • Procedure to collect and present information concerning the uniformity of application, precipitation rate, and general condition of an irrigation system and its components.

Irrigation design

  • Plan of an irrigation system with pipe sizing, head layout and valve location. 

irrigation frequency

  • Measure of the number of irrigations per unit time.

irrigation interval

  • Average time interval between the commencements of successive irrigations for a given field (or area).


Irrigation period

  • Time that it takes to apply one irrigation to a given design area during the peak consumptive-use period of the crop being irrigated.

Irrigation (water) requirement

  • Depth of water, exclusive of effective precipitation, stored soil moisture, or ground water, that is required for meeting crop evapotranspiration for crop production and other related uses. Such uses may include water required for leaching, frost protection, cooling and chemigation. -- Difference between  evapotranspiration and effective precipitation.
  • Quantity of water needed by the landscape to satisfy the evaporation, transpiration and other uses of the water in the soil.
  • Gross Irrigation Requirement - Total amount of water applied (or desired). See also irrigation water requirement.
  • Total Irrigation Requirement - including net crop requirement plus any losses incurred in distributing and applying and in operating the system.
  • Irrigation Water Requirement - Calculated amount of water needed to replace soil water used by the crop (soil water deficit), for leaching undesirable elements through and below the plant root zone, plus other needs; after considerations are made for effective precipitation.

Irrigation sagacity

  • Ratio of volume of irrigation water beneficially or reasonably used to the total volume of irrigation water that has left the region, both in a specified period of time.

Irrigation schedule

  • Procedure of establishing and implementing the time and amount of irrigation water to apply.
  • Determining when to irrigate and how much water to apply, based upon measurements or estimates of soil moisture or crop water used by a plant.
  • Set of specifications identifying times to turn on and off water to various zones of an irrigation system.

Irrigation set

  • Area irrigated at one time within a field.

Irrigation slope

  • Elevation difference along the direction of irrigation. Sometimes called irrigation grade.

Irrigation system

  • Physical components (pumps, pipelines, valves, nozzles, ditches, gates, siphon tubes, turnout structures) and management used to apply irrigation water by an irrigation method. All equipment required to convey water to or within the design area-- Set of components which includes (may include) the water source, water distribution network, control components and possibly other general irrigation equipment.  
  • Micro Irrigation System - is a low pressure and low volume system wherein water is applied to the soil surface as drops or small streams through emitters. Method of micro-irrigation wherein water is applied to the soil surface (or below the soil surface) as drops or small streams through emitters.  Discharge rates are generally less than 2 gph for single-outlet emitters and 3 gph per meter for line-source emitters.
  • Bubbler Irrigation - The application of water to flood the soil surface using a small stream or fountain. The discharge rates for point-source bubbler emitters are greater than for drip or subsurface emitters but generally less than 1 gpm.  A small basin is usually required to contain or control the water.
  • Surface Irrigation - Type of irrigation where water is distributed to the plant material by a ground surface distribution network possibly including rows or dikes.
  • Border Irrigation - Irrigation by flooding strips of land, rectangular in shape and cross leveled, bordered by dikes.  Water is applied at a rate sufficient to move it down the strip in a uniform sheet.  Border strips having no down field slope are referred to as level border systems.  Border systems constructed on terraced lands are commonly referred to as benched borders.  
  • Sprinkler Irrigation - A type of irrigation using mechanical devices with nozzles (sprinklers) to distribute the water by converting water pressure to a high velocity discharge stream or streams.
  • Center Pivot - Automated irrigation system consisting of a sprinkler lateral rotating about a pivot point and supported by a number of self-propelled towers.  Water is supplied at the pivot point and flows outward through the pipeline supplying the individual sprinklers or spray heads.
  • Large Rotating Sprinkler(s) - Are mounted on a trailer to deliver water in a circle.  The sprinkler and associated trailer are towed through the field by any of several means.
  • Portable Irrigation - Sprinkler system which is moved by uncoupling and picking up the pipes manually, requiring no special tools.  
  • Solid set/fixed System – The use of portable surface or permanently buried laterals totally covering the irrigated area or field. Typically several adjacent laterals or heads are operated at one time.  Portable laterals are typically removed from the field at end of germination, plant establishment, or the irrigation season and are replaced the next irrigation system. 


Kinematic viscosity

  • Measure of the resistance of a liquid to shear forces.


Lag time

  • Period between the time that the irrigation stream is turned off at the upper end of an irrigated area and the time that water disappears from the surface at the point or points of application.

Lath box

  • Wooden box that is placed in a ditch bank to transfer water from an irrigation ditch to the field to be irrigated.


  • Removal of soluble material from soil or other permeable material by the passage of water through it.

Leaching fraction [LF] {-}

  • Ratio of the depth of subsurface drainage water (deep percolation) to the depth of infiltrated irrigation water (see leaching requirement).

Leaching requirement

  • Quantity of irrigation water required for transporting salts through the soil profile to maintain a favorable salt balance in the root zone for plant development.


  • Linear dimension used to describe the quantity / amount / distance of pipe, conductor or similar material in various equations.

Length of run

  • Distance water must flow in furrows or borders over the surface of a field from the head to the end of the field.


  • Acronym for Low Energy Precision Application.

Limited irrigation

  • Management of irrigation applications to apply less than enough water to satisfy the soil water deficiency in the entire root zone.  Sometimes called " deficit" or "stress irrigation".

line source

  • Continuous source of water emitted along a line.


  • The textural class name of soil having a moderate amount of sand, silt, and clay. Loam soils contain 7-27%clay, 28-50%silt, and <52%sand.


  • Acronym for Low Pressure In Canopy.

Looped circuit

  • Piping system, usually a main line, which closes back on itself in a loop, thus providing water to any location from two routes.

Low Energy Precision Application [LEPA]

  • A water, soil, and plant management regime where precision down-in-crop applications of water are made on the soil surface at the point of use. Application devices are located in the crop canopy on drop tubes mounted on low-pressure center pivot and linear move sprinkler irrigation systems. 

Low Pressure In Canopy [LPIC]

  • Low-pressure in-canopy system that may or may not include a complete water, soil and plant management regime as required in LEPA. Application devices are located in the crop canopy with drop tubes mounted on low-pressure center pivot and linear move sprinkler irrigation systems.

Low head drainage

  • Condition in which water drains partially or completely out of the lateral line through the sprinkler head after each irrigation cycle is completed.


  • Isolated block of soil, usually undisturbed and in situ, for measuring the quantity, quality, or rate of water movement through or from the soil.



  • Water delivery pipelines that supply water from the control station to the manifolds.


Management allowable (allowed) depletion

  • See similar term, maximum allowable deficiency.
  • Desired soil moisture deficit at the time of irrigation.

Manufacturer’s coefficient of variation

  • Measure of the variability of discharge of a random sample of a given make, model, and size of micro-irrigation emitter, as produced by the manufacturer and before any field operation or aging has taken place; equal to the ratio of the standard deviation of the discharge of the emitters to the mean discharge of the emitters.


  • Pipeline that supplies water to the laterals.
  • Closely linked series of mainline piping supplying water to valves or laterals.

Master valve

  • See valve.

Matched precipitation rate

  • System or zone in which all the heads have similar precipitation rates is said to have matched precipitation rates.

Matric potential

  • Dynamic soil property and will be near zero for a saturated soil.  Matric potential results from capillary and adsorption forces.  This potential was formerly called capillary potential or capillary water.

Maximum allowable deficiency

  • See similar term, management allowed depletion.
  • Term used to estimate the amount of water that can be used without adversely affecting the plant and is defined as the ratio of readily available water to available water.

Maximum application rate

  • Maximum discharge at which sprinklers can apply water without causing significant translocation.

Median drop size

  • Diameter where half the sprinkler's water volume falls in drops smaller, and half falls in drops larger than the median size.
  • Drop size where 50%of the water volume occurs in drops greater than this size. 


  • Atmospheric conditions within or near a crop canopy.

micro irrigation

  • See irrigation system.


  • Acronym for male iron pipe thread. (Smith, 1997)

Mist irrigation

  • Method of micro-irrigation in which water is applied in very small droplets.

Mixed flow pump

  • See pump.

Moisture deficit, soil moisture depletion

  • Difference between actual soil moisture and soil moisture held in the soil at field capacity.

Moisture meter

  • Device that monitors or measures soil water content or tension.

Moisture sensor

  • Device that monitors or measures soil water content of tension.


  • Male nominal Pipe Threads.


Net positive suction head

  • Head that causes liquid to flow through the suction piping and enter the eye of the pump impeller. Net positive suction head available - Pressure head that is supplied (is available) to the eye of an impeller in a pump based on system characteristics.
  • Net positive suction head required - Minimum pressure head required at the eye of an impeller in a pump to prevent cavitation.


  • Named size which is usually not the actual dimension of the product. 

Non-point source pollution

  • Pollution originating from diffuse areas (land surface or atmosphere) having no well-defined source.

Non-saline sodic soil

  • Soil containing soluble salts that provide an electrical conductivity of saturation extract (ECe) less than 4.0 mmhos/cm and an exchangeable sodium percentage (ESP) greater than 15. Commonly called black alkali or slick spots.


  • Final orifice through which water passes from the sprinkler or emitter to the atmosphere.

Number of outlets

  • Term used to describe the number of outlets in a lateral.

Source: Irrigation Association 2014. Available: http://www.irrigation.org/defaultcontent.aspx?id=1243&terms=glossary