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Irrigation Glossary



Sail index Cross-sectional area per unit volume of water of the drop comprising the sprinkler spray.

Saline soil Salt affected soils are caused by excess accumulation of salts, typically most pronounced at the soil surface. Salts can be transported to the soil surface by capillary transport from a salt laden water table and then accumulate due to evaporation; they can also be concentrated in soils due to human activity. As soil salinity increases, salt effects can result in degradation of soils and vegetation.

Saline-sodic soil   Soil containing both sufficient soluble salts and exchangeable sodium to interfere with the growth of most crops.  The exchangeable sodium percentage (ESP) is greater than or equal to 15, and electrical conductivity of the saturation extract (ECe) is greater than 4 mmhos/cm.  It is difficult to leach because the clay colloids are dispersed.

Salinity Refers to the amount of salts dissolved in soil water.

Sand Soil particles ranging from 50 to 200 :m (0.05 to 0.2 mm) in diameter. 

Sandy Loam Topsoil in which plant roots grow well but where watering is difficult becasue the soil drains quickly. This soil benefits from short, frequent waterings.

Saturation (of soil) Condition where all soil pores / voids are filled with water.

Schedule   Method of specifying the dimensions and thus the allowable operating pressure of pipe. For a specific schedule rating, the wall thickness remains relatively constant for different pipe diameters, resulting in lower allowable operating pressures for larger diameter pipe.

Scheduling 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.

Scheduling coefficient A number that relates to the uniformity of coverage and how to operate the system to adequately irrigate the entire turf area.  It indicates the amount of extra watering time needed to adequately irrigate the driest areas..

Scheduling program  Set of specifications identifying times to turn on and off water to various zones of an irrigation system.

Semiarid climate 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.

Service line Section of piping connecting larger municipal supply line with water meter.

Service Panel An electrical box that contains either fuses or circuit breakers. Power from the utility enters the service panel, where it's divided up into branch circuits. Also referred to as a panel box or a main panel.

Set time Amount of time required to apply a specific amount of water during one irrigation to a given area, typically refilling the plant root zone to field capacity minus expected rainfall. 

Shutoff head Pressure head on the outlet side of a pump at which the discharge drops to zero.  Maximum pressure a pump will develop at a given speed.

Silt Loam A fine texured topsoil that holds minerals and water well. Most plants thrive in silt loam. However, puddling may occur if clay predominates over sand in composition .

Single leg profile  Precipitation rate profile of an individual sprinkler head operating at a known, constant pressure.

Siphon Closed conduit used to convey water across localized minor elevation raises in grade.  It generally has end sections below the middle section.  A vacuum pump is commonly used to remove air and keep the siphon primed.  The upstream end must be under the water surface.  Both ends must be under water, or the lower end must be closed to prime the siphon.

Siphon tube Relative short, light-weight, curved tube used to convey water over ditch banks to irrigate furrows or borders.

Silt Mineral portion of soil have particle sizes ranging from 0.05 to 0.002 mm in diameter.

Slide gate Head control valve, which slides on rails, used to control drainage or irrigation water.

Slip joint or Slip configurationConnection without threads (of PVC pipe or fittings) which is solvent welded.

Slope Is used to describe the steepness, incline, gradient, or grade of a straight line. A higher slope value indicates a steeper incline.A slope is derived from dividing the rise of an incline by it's run.

Sodic soil Non-saline soil containing sufficient exchangeable sodium to adversely affect crop production and soil structure.

Sodium adsorption ratio Portion of soluble sodium ions in relation to the soluble calcium and magnesium ions in the soil water extract.

Sodium adsorption ratio, adjusted Sodium adsorption ratio of a water adjusted for the precipitation or dissolution of CA2+ and Mg2+ that is expected to occur where a water reacts with alkaline earth carbonates with a soil.

Sodium percentage Percentage of total cations that is sodium in water or soil solution.

Soil Unconsolidated minerals and material on the immediate surface of the earth that serves as a natural medium for the growth of plants.

Soil horizon Layer of soil, usually approximately parallel to the soil surface, with distinct characteristics produced by soil forming processes.

Soil moisture (water) depletion (deficit) Difference between field capacity and the actual soil moisture in the root zone soil at any given time.  It is the amount of water required to bring the soil in the root zone to field capacity. 

Soil profile A vertical cross section through a soil which shows any layers or horizons of which the soil is composed.

Soil reservoir capacity Preferred term plant available water.

Soil series Lowest category of U.S. system of soil taxonomy.  A conceptualized class of soil bodies having similar characteristics and arrangement in the soil profile.

Soil water (moisture) All water stored in the soil.

Soil water characteristic curve Soil-specific relationship between the soil-water matric potential and soil-water content.

Soil water content Amount of water in a given volume (or weight) of soil.

Soil-water (moisture) deficit or depletion Depth of water required to bring a specific depth of soil to field capacity at a particular time. Preferred term soil moisture depletion.

Soil-water tension Measure of the tenacity with which water is retained in the soil.  It is the force per unit area that must be exerted to remove water from the soil.

Solenoid   Electromagnet which is connected to a controller and facilitates the opening and closing of automatic control valves (or valve-in-head sprinklers).

Solid set irrigation system System 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.


  • between sprinklers Distance from one sprinkler to the next one along a row.
  • between rows (of sprinklers) Distance between adjacent rows of sprinklers.
  • between drains Distance between parallel subsurface drain lines.
  • equilateral triangular spacing Sprinklers are spaced in an equilateral triangular pattern.
  • rectangular spacing Sprinklers are spaced in a rectangular pattern.
  • row spacing  Distance between the rows of sprinklers.See spacing between rows.
  • head to head spacing Sprinklers are spaced so that each head throws water to the adjacent heads.  
  • triangular spacing Sprinklers are spaced in a triangular pattern.

Species factor Factor or coefficient used to adjust reference evapotranspiration to reflect plant species.

Specific gravity Ratio of a substance's density (or specific weight) to that of some standard substance such as water.  For liquids, the standard is water at sea level and 60 F (SP. GR. = 1).

Specific speed Index of pump type related to impeller speed, discharge and total head.

Specific volume Volume occupied by a unit mass of fluid.

Specific weight Weight per unit volume of a substance.

Spile Conduit, made of lath, pipe or hose, placed through ditch banks to transfer water from an irrigation ditch to a field.

Spray irrigation Application of water by a small spray or mist to the soil surface, where travel through the air becomes instrumental in the distribution of water.

Sprinkler distribution pattern Water depth-distance relationship measured from a single sprinkler head.

Sprinkler (head)

  • Device for distributing water under pressure.
  • Nozzle or device, which may or may not rotate, for distributing water under pressure through the air.
  • Hydraulically operated mechanical device which discharges water through a nozzle or nozzles.
  • gear drive sprinkler Sprinkler containing gears as part of its rotational drive mechanism.
  • impact drive Sprinkler which rotates using a weighted or spring-loaded arm which is propelled by the water stream and hits the sprinkler body, causing movement.
  • rotor Sprinkler that rotates, but may more specifically refer to a gear driven sprinkler.
  • spray head   Sprinkler head that does not rotate.
  • valve-in-head   Sprinkler head having an integrally mounted valve.

Sprinkler irrigation   Method of irrigation in which the water is sprayed, or sprinkled, through the air to the ground surface.

Standard deviation[SD] {same as units of variable} Statistical term used to describe the distribution of values.

Standard dimension ratio Dimension Ratio is defined as the ratio of the diameter of a pipe to its wall thickness. Outside diameter is used for OD rated pipe while ID is used for ID rated pipe. Certain dimension ratios have been selected by convention and standards to be used for construction of pipe. These dimension ratios are referred to as standard dimension ratios.

Static discharge head Static energy components at the discharge of a pump including elevation and pressure.

Static head:  Energy associated with a static liquid system composed of elevation and pressure components.

Static lift Vertical distance between water source and discharge water levels in a pump installation.

Static water pressure Pressure in a closed system, without any water movement. Water pressure when the water is at rest.

Static suction head  Vertical distance from the pump centerline to the surface of the liquid when the liquid supply is above the pump

Station Circuit on a controller which has the ability to be programmed with a run time unique and separate from other circuits and provides power to one or more remote control valves (or valve-in-head sprinklers).

Stationary sray head because these heads do not move, rotate or pop-up they are the most maintenance free type of spray head.

Stress irrigation Management of irrigation water to apply less than enough water to satisfy the soil water deficiency in the entire root zone. Preferred term is limited irrigation or deficit irrigation.

Structure (soil) Combination or arrangement of primary soil particles into secondary units or peds.  The secondary units are characterized on the basis of size, shape, and grade (degree of distinctness).  Structural classes include granular, blocky, and columnar massive, platy, prismatic, among others.

Sub-humid climate 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.

Sub-irrigation Applying irrigation water below the ground surface either by raising the water table or by using a buried perforated or porous pipe system that discharges water directly into the plant root zone. ...

Submersible pump  Pump where the motor and pump are submersed below the water surface.

Subsurface drip irrigation   Application of water below the soil surface through emitters, with discharge rates generally in the same range as drip irrigation.  The method of water application is different from and not to be confused with sub-irrigation where the root zone is irrigated by water table control.

Suction (static) lift Vertical distance between the elevation of the surface of the water source and the center of the pump impeller.

Surface irrigation Type of irrigation where water is distributed to the plant material by a ground surface distribution network possibly including rows or dikes.

Surge irrigation Surface irrigation technique wherein flow is applied to furrows (or less commonly, borders) intermittently during a single irrigation set.

Surge pressure Water pressure caused by changes in water velocity in a pipe system.

Sweating A technique used to produce watertight joints between copper pipe fittings. A pipe and fittings are cleaned, coated with flux

Swing check (valve) Valve used in a pipeline which allows flow in only one direction.

Swing joint Threaded connection of pipe and fittings between the pipe and sprinkler which allows movement to be taken up in the threads rather than as a sheer force on the pipe.  Also used to raise or lower sprinklers to a final grade without plumbing changes.

System capacity Ability of an irrigation system to deliver the net required rate and volume of water necessary to meet crop water needs plus any losses during the application process.  Crop water needs can include soil moisture storage for later plant use, leaching of toxic elements from the soil, air temperature modification, crop quality, and other plant needs.

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