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Irrigation Glossary


Lag time (flood irrigation) {h, min} 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.


  • Secondary or side channel, ditch or conduit.  Also call "branch drain" or "spur".
  • Water delivery pipeline that supplies irrigation water from the main line to sprinklers or emitters.
  • The pipe installed downstream from the control valve on which the (sprinkler heads or) emission devices are located.

Lath box Wooden box that is placed in a ditch bank to transfer water from an irrigation ditch to the field to be irrigated (preferred term is spile).

Leaching 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 [LR] 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.

Length 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.

LEPA 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.

Loam is a soil composed of sand, silt, and clay in relatively even concentration (about 40-40-20% concentration respectively), considered ideal for gardening and agricultural uses. Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils.

  • Loams are gritty, moist, and retain water easily. In addition to the term loam, different names are given to soils with slightly different proportions of sand, silt, and clay: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam.
  • Loam soil feels mellow and is easy to work over a wide range of moisture conditions. A soil dominated by one or two of the three particle size groups can behave like loam if it has a strong granular structure, promoted by a high content of organic matter. However, a soil that meets the textural definition of loam can lose its characteristic desirable qualities when compacted, depleted of organic matter, or has clay dispersed throughout its fine-earth fraction.
  • Loam soil is ideal for growing crops because it retains nutrients well and retains water while still allowing the water to flow freely. This soil is found in a majority of successful farms in regions around the world known for their fertile land.

LPIC Acronym for Low Pressure In Canopy.

Looped circuit Piping system, usually a main line, that 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.


  • Device for measuring deep percolation from a soil profile, usually consisting of an enclosed volume of undisturbed soil with some means of collecting drainage water.  It may also include some method of measuring changes in the volume of stored soil water. 
  • Isolated block of soil, usually undisturbed and in situ, for measuring the quantity, quality, or rate of water movement through or from the soil.
  • Device and monitoring system used to measure the evapotranspiration (ET) rate using a container closed at the bottom and with the top flush with surrounding grade and planted with turf. After rainfall and irrigation application are accounted for, daily change in the weight of the lysimeter is directly related to ET.

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