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Irrigation Glossary


main (mainline):

  • Water delivery pipelines that supply water from the control station to the manifolds. (ASAE EP405.1 DEC99)
  • Pipe usually under constant pressure which supplies water from the point of connection to the control valves (or valve-in-head sprinklers). (Rain Bird, 1997)

management allowable (allowed) depletion (deficit) *[MAD] {%, -} (11/6/99):

  • See similar term, maximum allowable deficiency. 
  • Desired soil moisture deficit at the time of irrigation. (On-Farm Committee, 1979) 
  • Portion of available water that is scheduled to be used prior to the next irrigation.   
  • Planned soil moisture deficit at the time of irrigation.  (NRCS, 1997)

manipulated soils: See disturbed soils.
manufacturer's coefficient of variation* [Cv] {-}: 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. (ASAE, 1998)

  • Pipeline that supplies water to the laterals. (ASAE, 1998) 
  • Closely linked series of mainline piping supplying water to valves or laterals. (Carruthers, B. 1999, Unpublished)

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. (Monroe, 1993)
matric potential {ft, m}: 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. (NRCS, 1997)
maximum allowable deficiency*  [MADp] {-}:

  • See Fig. 1 at end of document. 
  • 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. (James, 1988).

maximum application rate {in./h, mm/h}: Maximum discharge at which sprinklers can apply water without causing significant translocation. (NRCS, 1997)
median drop size {in., mm}:

  • Diameter where half the sprinkler's water volume falls in drops smaller, and half falls in drops larger than the median size. (Solomon et al, 1996) 
  • Drop size where 50%of the water volume occurs in drops greater than this size.  (Contractor, 1999)

microclimate: Atmospheric conditions within or near a crop canopy. (NRCS, 1997)
microclimate factor: See coefficient.
micro irrigation: See irrigation system.
MIPT: Acronym for male iron pipe thread. (Smith, 1997)
mist irrigation: Method of micro-irrigation in which water is applied in very small droplets. (ASAE, 1998)
mixed flow pump: See pump.
moisture deficit, soil moisture depletion {in., mm}: Difference between actual soil moisture and soil moisture held in the soil at field capacity. (NRCS, 1997)
moisture meter: Device that monitors or measures soil water content or tension. (Carruthers, B. 1999, unpublished)
moisture sensor:

  • Instrument which monitors soil water content... (Rain Bird, 1997)
  • Device that monitors or measures soil water content of tension. (Carruthers, B, 1999, unpublished)

MPT {in., mm}: Male nominal Pipe Threads. (Rain Bird, 1997)
multistage pump: See pump.
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net irrigation: See irrigation, net
net irrigation requirement [NIR] {in., mm}: See irrigation requirement, net.
net positive suction head*[NPSH] {ft, m} (11/6/99): Head that causes liquid to flow through the suction piping and enter the eye of the pump impeller. (ASAE, 1998) 

  • net positive suction head available* [NPSHA] {ft, m} (approved via RM): Pressure head that is supplied  (is available) to the eye of an impeller in a pump based on system characteristics. (Reference Manual, ch. 4) 
  • net positive suction head required*[NPSHR] {ft, m}  (approved via RM): Minimum pressure head required at the eye of an impeller in a pump to prevent cavitation. (Reference Manual, ch. 4)

net precipitation rate: See precipitation rate
net (irrigation) water requirement {in., m}: Same as net irrigation requirement.
nominal {in., m}: Named size which  is usually not the actual dimensions of the product.  i.e. a half inch schedule 40 pipe is not  1/2 inch ID or OD.
nonbeneficial use: See use.
nonconsumptive use: See use.
nonpoint source pollution: Pollution originating from diffuse areas (land surface or atmosphere) having no well-defined source. (NRCS, 1997)
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. (NRCS, 1997)
nozzle: Final orifice through which water passes from the sprinkler or emitter to the atmosphere. (Rain Bird, 1997)
number of outlets*[No] {-}: Term used to describe the number of outlets in a lateral.

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operating pressure {psi, kPa}:

  • Actual head pressure remaining at the sprinkler head after the total pressure loss from the city main to the critical head is subtracted from the starting static pressure. (Texas Natural Resource Conservation Commission) 
  • Pressure at which a system of sprinklers operates, usually measured at the base or nozzle of a sprinkler. (Rain Bird, 1997)

opportunity time {min., h}: Time that water inundates the soil surface with opportunity to infiltrate. (NRCS, 1997)
orchard valve: See valve.

  • Opening with a closed perimeter through which water flows.  Certain shapes of orifices are calibrated for use in measuring flow rates. (ASAE, 1998) 
  • Opening in system component such as pipe, tubing, or nozzle. (Rain Bird, 1997)

osmotic potential {ft, m}: Potential attributable to the presence of solutes in the soil- in other words, to the soil solution.  (Brady, 1990)
osmotic pressure (potential): See potential. {psi, ft, kPa, m}
oven dry:

  • Drying of soil samples in an over for a sufficient period of time to reach a constant weight. (Black, 1965) 
  • Refers to soil samples that have been dried in an oven at 105 C for 24 hours ...  (Contractor, 1999)

overhead irrigation: Same as sprinkler irrigation.
overlap: Area which is watered by two or more sprinklers. (Rain Bird, 1997)