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Irrigation Glossary


sail index {ft2/gal, m2/m3}:

  • Cross-sectional area per unit volume of water of the drop comprising the sprinkler spray. (Solomon, 1996) 
  • Cross sectional area of spray (drops) per unit volume of water. (Contractor, 1999)

saline soil {-}:

  • Non-sodic soil containing soluble salts in such quantities that they interfere with the growth of most crops ... (ASAE, 1998) 
  • Soil that has sufficient soluble salts to interfere with crop growth.  ... (Hess, 1999) 
  • Non-sodic soil containing sufficient soluble salts to impair its productivity for growing most crops. The electrical conductivity (ECe) of the saturation extract is greater than 4 mmhos/cm, and exchangeable sodium percentage (ESP) is less than 15; i.e., non-sodic. The principal ions are chloride, sulfate, small amounts of bicarbonate, and occasionally some nitrate. Sensitive plants are affected at half this salinity, and highly tolerant ones at about twice this salinity. (NRCS, 1997)

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. (NRCS, 1997)
salinity: Refers to the amount of salts dissolved in soil water.

  • Soil particles ranging from 50 to 200 :m (0.05 to 0.2 mm) in diameter.  
  • Soil material containing 85%or more in this size range. (ASAE, 1998)

saturation (of soil) {in./in., in./ft, %, mm/ m }: Condition where all soil pores / voids are filled with water. (NRCS, 1997)
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.
schedule, irrigation: See 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. (NRCS, 1997)

scheduling coefficient* [SC] {-}: 

  • 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. (Solomon, 1988; Zoldoske et al, 1994) 
  • Numerical expression which serves as an index of the uniformity of water application to a give area within a specific geometric arrangement of sprinklers (e.g. triangular or square).  Used to measure the uniformity of landscape irrigation systems. (Rain Bird, 1997)

scheduling program:  Set of specifications identifying times to turn on and off water to various zones of an irrigation system.
SDR: See standard dimension ratio.
semiarid climate: See climate.
service factor {-} 
service line: Section of piping connecting larger municipal supply line with water meter. (Carruthers, B., unpublished)
set time {h, min.}:

  • Elapsed time between the beginning and end of water application to an irrigation set. (ASAE, 1998) 
  • 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.  (NRCS, 1997)

shutoff head {ft, kPa, m}: 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. (ASAE, 1998)
single leg profile: Precipitation rate profile of an individual sprinkler head operating at a known, constant pressure. (Oliphant, 1989)
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. (NRCS, 1997)
siphon tube: Relative short, light-weight, curved tube used to convey water over ditch banks to irrigate furrows or borders. (ASAE, 1998)
silt: Mineral portion of soil have particle sizes ranging from 0.05 to 0.002 mm in diameter. Buckman and Brady, 1961
slide gate: Head control valve, which slides on rails, used to control drainage or irrigation water. (ASAE, 1998)
slip configuration or slip joint: Connection without threads (of PVC pipe or fittings) which is solvent welded. (Rain Bird, 1997)
sodic soil: Non-saline soil containing sufficient exchangeable sodium to adversely affect crop production and soil structure. ...  (ASAE, 1998)
sodium adsorption ratio*[SAR] {-}: Portion of soluble sodium ions in relation to the soluble calcium and magnesium ions in the soil water extract ...  (ASAE, 1998)
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. ...  (NRCS, 1997)
sodium percentage {%}: Percentage of total cations that is sodium in water or soil solution. (ASAE, 1998)
soil: Unconsolidated minerals and material on the immediate surface of the earth that serves as a natural medium for the growth of plants. (ASAE, 1998)
soil horizon: 

  • Layer of soil differing from adjacent genetically related layers in physical, chemical, and biological properties or characteristics. (ASAE, 1998) 
  • Layer of soil, usually approximately parallel to the soil surface, with distinct characteristics produced by soil forming processes. (Hess, 1999)

soil moisture (water) depletion (deficit)*[SMD] {in., mm}: 

  • 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. (On-Farm Committee, 1979) 
  • Amount of water required to fill the plant root zone to field capacity. (Burt, 1998)

soil profile:

  • Vertical section of the soil from the surface through all its horizons into the parent material. (ASAE, 1998) 
  • A vertical cross section through a soil which shows any layers or horizons of which the soil is composed. (Hess, 1999)

soil reservoir capacity [SRC] {in., mm}: 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. (ASAE, 1998)
soil structure: See structure.
soil texture: See texture.
soil water (moisture) {in., mm}: All water stored in the soil. (ASAE, 1998)
soil water characteristic curve: Soil-specific relationship between the soil-water matric potential and soil-water content. (ASAE, 1998)
soil water content* [WC%, θ] {%, in./ft, in./in., mm/m}  (11/6/99)

  • Amount of water in a given volume (or weight) of soil. ... (NRCS, 1997)
  • Amount of water in a soil sample based on dry weight of the soil sample. (Reference Manual)

soil-water (moisture) deficit or depletion [SWD] {in., mm}:

  • Depth of water required to bring a specific depth of soil to field capacity at a particular time. (ASAE, 1998) 
  • Preferred term soil moisture depletion.

soil-water potential: See potential.
soil-water tension {bars, atm., kPa}: 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. ...  (NRCS, 1997)
solenoid: Electromagnet which is connected to a controller and facilitates the opening and closing of automatic control valves (or valve-in-head sprinklers). (Rain Bird, 1997)
solid set irrigation system: See irrigation system.
spacing {ft, m}:

  • between sprinklers [Ss, S] (11/6/99): Distance from one sprinkler to the next one along a row. 
  • between rows (of sprinklers) [Sr] (11/6/99): Distance between adjacent rows of sprinklers. 
  • between drains [Sd]: Distance between parallel subsurface drain lines. 
  • equilateral triangular spacing [S]: 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. (Monroe, 1993) See spacing between rows. 
  • head to head spacing [S]: Sprinklers are spaced so that each head throws water to the adjacent heads.   
  • triangular spacing [S]: Sprinklers are spaced in a triangular pattern.

species factor: See coefficient.
specific gravity*[SP. GR. ] {-}: 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*[Ns] {rpm}: Index of pump type related to impeller speed, discharge and total head. (ASAE, 1998)
specific volume [νs] {ft3/lb, m3/kg}: Volume occupied by a unit mass of fluid. (Reference Manual).
specific weight* [(, or SW] {lb/ft3, kg/m3}: 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. (ASAE, 1998)
spray head: See sprinkler head.
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. (ASAE, 1998) (In some countries other than the US, sprinkler irrigation is called spray irrigation.)
sprinkler distribution pattern:

  • Water depth-distance relationship measured from a single sprinkler head. (NRCS, 1997)
  • Two dimensional water depth-distance relationship measured from a single (or multiple) sprinkler head(s).

sprinkler (head):

  • Device for distributing water under pressure. (ASAE, 1998) 
  • Nozzle or device, which may or may not rotate, for distributing water under pressure through the air. (NRCS, 1997) 
  • Hydraulically operated mechanical device which discharges water through a nozzle or nozzles. (Rain Bird, 1997) 
  • 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. (Rain Bird, 1997)
  • 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. (ASAE, 1998)
sprinkler irrigation system: See irrigation system.
sprinkler precipitation rate: See precipitation rate.
sprinkler profile: See profile (sprinkler)
standard deviation* [SD] {same as units of variable}: Statistical term used to describe the distribution of values.
standard dimension ratio*[SDR] {-} (approved via RM): 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. (ASAE, 1985)
static discharge head: See head.
static head: See head.
static lift {ft, m}: Vertical distance between water source and discharge water levels in a pump installation. (ASAE, 1998)  Same as total static head.
static pressure {psi, kPa, m}:

  • Pressure in a closed system, without any water movement. (Rain Bird, 1997 
  • Water pressure when the water is at rest. (Monroe, 1993) 
  • See also head.

static suction head: See head.
static suction lift: See suction lift.
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). (Rain Bird, 1997)
stationary sprinklers: Irrigation having underground piping with risers and sprinklers.
stress irrigation: Management of irrigation water to apply less than enough water to satisfy the soil water deficiency in the entire root zone  (ASAE, 1998). Preferred term is limited irrigation or deficit irrigation. (ASAE, 1998)
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).  (Soil, 1996) 
  • Combination of various soil particle types into a uniform mixture that behaves as a single unit. Structural classes include granular, blocky, and columnar massive, platy, prismatic, among others. (Monroe, 1993) 
  • Aggregation of primary soil particles, into units which are separated from each other by surfaces of weakness. An individual natural soil aggregate is called a ped in contrast to a clod caused by disturbance, or a concretion caused by cementation. (Hess, 1999)

sub-humid climate: See climate.

  • Application of irrigation water below the ground surface by raising the water table to within or near the root zone. (ASAE, 1998) 
  • 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. ...  (NRCS, 1997)

submersible pump: See pump.
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. (ASAE, 1998)
suction (static) lift {ft, m}: Vertical distance between the elevation of the surface of the water source and the center of the pump impeller. (ASAE, 1998)
surface irrigation: See irrigation systems.
surge irrigation: See irrigation systems.
surge pressure* [ps] {psi, kPa}: Water pressure caused by changes in water velocity in a pipe system.
swing check (valve): See valve.
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. (Rain Bird, 1997)
system capacity {gpm/ac ? or gpm, m3/ha}: 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. (NRCS, 1997)
system precipitation rate: See precipitation rate.
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tail water: 

  • Water in a stream or canal, immediately downstream from a structure. 
  • Excess irrigation water which reaches the lower end of a field. (ASAE, 1998)

tensiometer: Instrument, consisting of a porous cup filled with water and connected to a manometer or vacuum gauge, used for measuring the soil-water matric potential. (ASAE, 1998)
textural class:

  • Classification used to convey an idea of the textural makeup of soils and to give an indication of their physical properties. Three broad groups of these classes are recognized - sands, loams, and clays. Within each group specified textural class names have been devised (i.e. loamy sand). (Brady, 1990) 
  • Classification name given a soil because of the particular size groups of particles found in the "A" horizon. (Contractor, 1999)

texture (soil):

  • Relative proportions of sand, silt and clay in a given soil. (Monroe, 1993)
  • Relative proportions of the various soil separates in a soil as described by the classes of soil texture...  (Soil, 1996)

thrust block: Normally, concrete poured in place at changes in direction of water flow in piping systems (tees, ells ... ) to prevent movement of the pipe. (Sneed, R. 1999. Unpublished)
tilth: Physical condition of the soil in relation to plant growth. (Brady, 1990; Drip, 1997)
time*[t] {s, min, h, day, fraction} (11/6/99)Term used to describe the duration of an operation, e.g. an irrigation event.
total dissolved solids [TDS] {ppm, mg/L}: Total dissolved mineral constituents of water. (NRCS, 1997)
total dynamic head: See head.
total static head: See static lift.
total suction head: See head.
total water holding capacity [TWHC] {in., mm}: Preferred term is Plant Available Water.
trajectory {degrees}: Angle above horizontal of the stream of water as it leaves the sprinkler head. (Rochester, 1995)
translocation: Movement of water to other areas than where it was applied. (NRCS, 1997)
transpiration* [T] {in./day, mm/day}: 

  • Process of plant water uptake and use, beginning with absorption through the roots and ending with transpiration at the leaf surfaces. See also evapotranspiration.  (NRCS, 1997) 
  • Liquid movement of water from the soil, into the roots, up the plant stems, and finally out of the plant leaves into the air as vapor. (Burt, 1998)

traveler (traveling gun) irrigation: See irrigation system.
triangular spacing: See spacing.
trickle irrigation: See irrigation system.
turbine pump: See pump, vertical turbine.
turbulent flow: Flow in which the fluid particles move in an irregular random manner, in which the head loss is approximately proportional to the second power of velocity. (ASAE, 1998)
turgid: State of a plant cell when the cell wall is rigid due to the hydrostatic pressure of liquid in the cell. (Hess, 1999)
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unavailable soil water {in./ft, mm/m }:Portion of water in a soil held so tightly by adhesion and other soil forces that it cannot be absorbed by plants rapidly enough to sustain growth. ...  (ASAE, 1998)

  • Term describing how evenly water is applied by overlapping sprinklers. (Smith, 1997) 
  • Evenness of precipitation over a given area.  (Contractor, 1999) 

uniformity coefficient:

  • irrigation [] {-,%}: Characteristic of the areal distribution of water in a field as the result of an irrigation. 
  • soil [] {-}: Ratio of the D60 size particles passing a screen to the D10 size of a granular material. (ASAE, 1998)

uniformity coefficient (Christiansen's)* [CU, CCU] {fraction, %}: Measure of the uniformity of irrigation water application. The average depth of irrigation water infiltrated minus the average absolute deviation from this depth, all divided by the average depth infiltrated. (ASAE, 1998)
union: Pipe fitting used to connect two lengths of pipe in such a way that neither has to be rotated .
unreasonable uses: See uses.
unsaturated zone: Part of the soil profile in which the voids (pore spaces) are not completely filled with water. (ASAE, 1998)
usable precipitation: See effective precipitation.

  • consumptive: Total amount of water taken up by vegetation for transpiration or building of plant tissue, plus the unavoidable evaporation of soil moisture, snow, and intercepted precipitation associated with vegetal growth. (ASAE, 1998) 
  • nonconsumptive: Water that leaves the selected region and not considered consumptive. Examples are runoff, deep percolation, and canal spills.  (Burt et al, 1997) 
  • beneficial [BU]: Beneficial use of water supports the production of crops: food, fiber, oil, landscape, turf, ornamentals, or forage. ...  (Burt et. al 1997) 
  • nonbeneficial: Water utilized in plant growth which can not be attributed as beneficial. 
  • reasonable: In the context of irrigation performance, all beneficial uses are considered to be reasonable uses. Non-beneficial uses are considered to be reasonable if they are justified under the particular conditions at a particular time and place. (Burt et at, 1997) 
  • unreasonable: Unreasonable uses are non-beneficial uses that, furthermore, are not reasonable; that is, they are without economic, practical, or other justification. (Burt et al, 1997)