Irrigation Glossary

Main (mainline)

Water delivery pipelines that supply water from the control station to the manifolds.
Pipe usually under constant pressure which supplies water from the point of connection to the control valves (or valve-in-head sprinklers).

Management allowable (allowed) depletion (deficit)

Desired soil moisture deficit at the time of irrigation.
Portion of available water that is scheduled to be used prior to the next irrigation.
Planned soil moisture deficit at the time of irrigation.

Manipulated soils Soils with soil profiles that have been altered because of earth-moving activities.

Manufacturer's coefficient of variation 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.

Manifold

Pipeline that supplies water to the laterals.
Closely linked series of mainline piping supplying water to valves or laterals.

Master valve Valve used to protect the landscape from flooding in case of a ruptured main or malfunctioning downstream valve. The master valve is installed on the mainline after the backflow preventer (in some systems).

Matched precipitation rate System or zone in which all the heads have similar precipitation rates is said to have matched precipitation rates.

Matric potential 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.

Maximum allowable deficiency 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.

Maximum application rate Maximum discharge at which sprinklers can apply water without causing significant translocation.

Median drop size

Diameter where half the sprinkler's water volume falls in drops smaller, and half falls in drops larger than the median size.
Drop size where 50%of the water volume occurs in drops greater than this size.

Microclimate Atmospheric conditions within or near a crop canopy.

Microclimate factor: Factor or coefficient used to adjust reference evapotranspiration to reflect the microclimate of an area.

Micro irrigation: also known as drip irrigation or trickle irrigation is an irrigation method which minimizes the use of water and fertilizer by allowing water to drip slowly to the roots of plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters.

MIPT Acronym for male iron pipe thread.

Mist irrigation Method of micro-irrigation in which water is applied in very small droplets.

Mixed flow pump Centrifugal pump in which the pressure is developed partly by centrifugal force and partly by the lifting action of the impellers on the water.

Moisture deficit, soil moisture depletion. Difference between actual soil moisture and soil moisture held in the soil at field capacity.

Moisture meter Device that monitors or measures soil water content or tension.

Moisture sensor Device that monitors or measures soil water content of tension.

MPT Male nominal Pipe Threads.

Multistage pump Pump having more than one impeller mounted on a single shaft.