Micro-irrigation includes a wide variety of low-volume, small-diameter water application devices. These include the rowcrop and individual emitters used in trickle or drip irrigation. It also includes the microspray heads and micro-sprinklers that broadcast water several feet. Collectively, these devices are called micro-irrigation devices because they deliver water primarily to individual plants or small areas.
For nursery and greenhouse production the emitter systems used are rowcrop tubings (rowcrop tape), individual emitters, and spray jets and stakes. These are discussed in more detail in the following sections.
Rowcrop tubing has emitters either designed into the tubing itself or welded into the tubing at regular intervals. The tubing with emitters designed into it looks like a tape because it collapses flat. The tubing with emitters welded into it is a heavier wall material with a rounder shape due to the emitter.
Wall thickness of the first material runs from 4 mils (0.004 in.) to 25 mils (0.025 in.). Emitter spacing can be 2, 6, 9, 18, 24, or 36 in. The tubing wets a continuous strip of ground with an even discharge along its length.
The rowcrop tubing can be placed under shrub areas, ground covers, tree plantings and irregular turf areas. In loamy to heavy clay soils, the tubing should be laid out in laterals that are spaced 16 to 24 in. apart. In very sandy soils, the laterals should be 12 to 16 in. apart.
The individual emitter is another micro-irrigation device that is attached to 1/2 in. or 3/4 in. polyethylene pipe on a spacing determined by the shrub or tree spacing.
There are usually one or more individual emitters per plant. Trees and shrubs have a different year-round water need than a bed of annuals and thus would have separate systems. For water conservation purposes, the system must be designed for the individual plants rather than broadcasting water over a large area to water one plant.
Spray jets include both micro-sprayers and microsprinklers and work better than rowcrop tubing or individual emitters on certain soils. They are better on sandy soils with little water-holding capacity or on special problem soils that tend to seal over to slow water infiltration. In addition, spray jets are ideal for many landscape plants that are shallow-rooted and closely planted.
Spray jets work well in large plantings of flowering annuals or under large trees - as long as the emitter is safe from vandalism.
These devices are available in a range of flow rates from 10 to 20 gph and have several distribution patterns. Spray diameters can be a few inches to several feet. Micro-sprayers emit water from an orifice onto a deflector plate.
Clogging can be a problem for the small emitters in rowcrop tubing, although the problem is not as great with the turbulent flow design now used. However, spray jets have larger emitters so debris passes through.
A combination of irrigation systems may be needed for a landscape. Use sprinklers in the large open areas and micro-irrigation devices in heavily used or odd shaped areas near people, walkways, or parking lots.