YOUR BEST PRACTICE
We are no longer working with measuring inches of water per acre, rather milliliters per square foot.
Greenhouse tomatoes are irrigated with one emitter supplying water to two stakes in the plant.
per acre, with a fraction of water usage required by conventional field production.
In Controlled Environment Agriculture, growers utilize conventional, root manipulating and cloth containers, as well as upright and lay flat bags. There is also a choice of soil or soilless media. The choice of substrate determines frequency and duration of the irrigation cycle. This method of frequent irrigation is called pulse irrigation and has led to advances in irrigation controllers.
In selecting an application method, the grower has several options governed by the container size, plant and media chosen. The use of microirrigation helps avoid water on the foliage and thus reduces the potential for disease.
There are several options when choosing irrigation emitters. The pressure compensating emitter maintains the same output rate regardless of the supply line pressure, if it stays between 15 and 50 psi. In addition, you can select a non- drip or non-leaking emitter that ceases output once pressure drops below a set pressure. By selecting non-drip or non- leaking pressure compensating emitters, all drippers turn on and off at the same time so that every plant receives the same amount of water and nutrients. This
26 Irrigation TODAY | Spring 2021
uniformity of application gives the grower predictable results, potentially aligning harvest with demand.
Additionally, the grower has options on what type of output device works best for a given application. One option is the drip ring, which is available in different diam- eters depending on the container size. These rings have multiple drip points that encircle the container, providing good application for containers up to 7-gallon size.
Another option is the drip stake. These are connected to the emitter with a small spaghetti tube and supply water to one point in the container. One emitter can supply multiple drip stakes, depending on the desired water volume and application rate being supplied to each plant. Quite often, growers will use multiple drip stakes per container, with drippers from more than one emitter. This redundancy provides a safety net in the event of an issue with one emitter.
The last option for water application is a spray stake that distributes water in a spray pattern instead of at specific points. The spray stakes are available in different angled patterns and flow rates depending on the container size chosen. The best use is for containers 7 gallons and larger. Typically, the spray stake is placed at the outer edge of the container and the output pointed toward the plant. Multiple stakes are often used in large containers to provide better coverage. Stakes are also available with a 45-degree downward angle. When used in smaller containers, they help avoid overspray, keeping all the water in the desired container. The use of spray stakes helps avoid channeling, which is when water moves quickly down the container without enough horizontal coverage.
When installed directly into the supply line, the spray stakes are not pressure compensating. To adjust for this, a 15 to 30 psi pressure regulator should be included in each zone to ensure proper operating pressure and better uniformity of volume and coverage.
These examples of microirrigation tech- nology advances help growers gain more control over the production of their crops and allow for increased production yield.
Using multiple drip stakes with drippers from more than one emitter provides a safety net in the event of an issue with one emitter.
Steve Brown Horticulture based in Maitland, Florida.
irrigationtoday.org
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