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Irrigation Glossary Page 5 of 7 <br />Plant Available Water <br />The available water located in the root zone. Calculated as the root zone depth multiplied <br />by the available water capacity. [%, decimal, in/ft. m/m] <br />Pore Space <br />Empty space between soil particles that is normally filled with either air and/or water. <br />Precipitation Rate <br />The depth of water applied to the soil per unit of time. [in/hr, mm/hr]. <br />Pressure <br />The measurement of force within a system. This is the force that moves water through <br />pipes, sprinklers and emitters. Static pressure is measured when no water is flowing and <br />dynamic pressure is measured when water is flowing. Pressure and flow are affected by <br />each other. [bars, psi, kPa) <br />¦ Pressure Regulator <br />A device that maintains a constant downstream pressure (can not increase pressure). <br />' Pump <br />Converts mechanical energy into hydraulic energy (pressure and/or flow). A centrifugal <br />pump is the most common type used for irrigation. <br />Pump Efficiency <br />Ratio of the water power produced by the pump to the power delivered to the pump by the <br />motor. [%, decimal) <br />' Pumping Plant Efficiency <br />The ratio of the output power of the water (pressure and flow) to the input power of the <br />driving motor. Either directly measured, or calculated by multiplying the motor efficiency by <br />the pump efficiency. [%, decimal] <br />' PVC <br />Polyvinyl Chloride. Plastic material widely used in irrigation for pipe and fittings because it <br />is light, inexpensive, easy to assemble, and can have a long useful life. It is typically buried. <br />Rain Shut-Off Device <br />A device typically used with lawn and garden irrigation controllers that prevent them from <br />opening irrigation valves when a specified amount of rain falls. <br />Root Zone <br />Also referred to as the root depth or effective rooting depth. The depth or volume of soil <br />from whim plants effectively extract water from. Typically this is defined as the depth of soil <br />' containing 80 percent of the plant roots. [ft, m) <br />Salinity (Saline) <br />Concentration of salts in irrigation water. High concentrations can limit the crops ability to <br />' take up and use the water in the soil. [dS/m, mg/l, ppm] <br />Siphon Tube <br />Relatively short, light-weight, curved tube used to convey water over ditch banks to irrigate <br />furrows or borders. <br />Soil Moisture Deficit <br />Also known as soil moisture depletion. The difference between field capacity and the actual <br />soil water content in the root zone. [%, decimal, in/ft, m/m] <br />http://irrigatioi.wsu.edti/glossary.php <br />1/7/2008 <br />84