Here are some links to pages that will help you learn more about irrigation automation.

Take a short quiz about water and irrigation. (The answers are upisde down at the bottom of the page)
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What are the options and benefits of irrigation automation?
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What may be some future developments in irrigation automation?
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The need for more efficient water use

Increased population growth and urbanization across the country has greatly increased the competition for limited water resources. Abundant water may not be available for agricultural production (including greenhouses) in the future. Thus, it is crucial for the future of the floriculture industry to develop methods to use water as efficiently as possible. Many growers over-apply water, or use relatively inefficient irrigation systems, such as overhead sprinklers or hand-held watering wands. Irrigation automation based on plant water use would save water and improve efficiency of water and labor use in commercial greenhouses.

Irrigation and runoff

Over-application of water not only results in an inefficient use of water, but also is the main cause of fertilizer runoff. In recent years, new state laws have been passed that regulate the amount of runoff from all forms of agriculture, including floriculture (e.g., Maryland’s Water Quality Improvement Act). To comply with new regulations, more efficient methods of fertilization and irrigation need to be implemented. There has been extensive research over the last few years to develop fertilizer guidelines for greenhouse crops. Although detailed fertilizer guidelines are now available for many greenhouse crops, leaching of nutrients (nitrate and phosphate in particular) depends greatly on the amount of water that is applied. The simplest way to minimize runoff is to only apply the amount of water plants need. However, one very simple question has received very little attention in past research: How much water do plants need?

Currently, reliable irrigation guidelines are the missing link in minimizing fertilizer runoff and optimizing water use efficiency. Since irrigation efficiency and runoff are closely linked, both issues can be addressed simultaneously by applying only the amount of water needed by the plants. Such a solution is much simpler and cheaper than collecting and treating runoff after it has left the greenhouse, for example with the use of constructed wetlands.

Benefits of efficient water use

In addition to decreased water use and a reduction in leaching and runoff, better control of irrigation provides growers with greater control over plant quality. Improving irrigation efficiency is recommended as a cultural practice in integrated pest management to prevent Pythium and Phytophthora infection . Reducing irrigation also reduces elongation of commercial bedding plants, such as marigold. Because elongation is very sensitive to mild drought, it may be possible to control the substrate water status at a level that reduces stretching, without any long-term detrimental impact on growth or plant quality. Irrigation automation may allow growers to reduce elongation by limiting water, as a supplement to or replacement for chemical growth retardant applications. Unfortunately, there currently is no method to irrigate plants automatically according to water use in commercial greenhouse production.

Measuring and controlling substrate water content

A relatively simple way to make irrigation more efficient is to only irrigate plants when they actually need water, and with the amount of water they need. That sounds easier than it is, because how do you know when a plant actually needs water? Our approach to answering that question is to measure the water content of the substrate and irrigate with a small amount of water as the water content of the substrate drops below a particular, grower-defined set point.

We have been using ECH2O moisture probes (Decagon Devices, Pullman WA) which can be installed in the substrate, and we have developed an irrigation controller that can maintain the volumetric water content of the substrate in 16 separate containers automatically and over prolonged periods. Krishna described this controller in his poster for the 2005 meetings of the ASHS, for which he won 1st prize in the graduate student poster competition.

This irrigation controller is based on ECH2O moisture probes connected to Campbell Scientific dataloggers and peripherals. The datalogger program that runs the system is available from this web page in both PDF and CSI format (the actual program is written in CSI format, using Campbell Scientific’s EDLOGW software).

The basic idea behind this irrigation approach is simple: as plants use water, the amount of water in the substrate decreases. This is measured by the controller, which automatically replenishes the substrate with water when needed. This results in water applications that are directly related to the amount of water used by the plants. On a sunny day when plants use a lot of water the substrate water content will drop faster, and the irrigation controller will apply water more frequently than on a cloudy day. Thus, the amount of irrigation truly depends on the water use of the crop.

Does this approach to irrigation really work?

In research at the Center for Applied Nursery Research in Dearing, GA, we used ECH2O-10 probes, interfaced to a datalogger, to control irrigation of hydrangeas. Substrate water levels range from 8 to 20% (20% was near saturation for this bark-based substrate). There was no difference in growth among plants grown in substrates with 14, 17, and 20% water content, but differences in the amount of water applied and leached were huge . For example, during a 65 day period, from early May to early July, the 14% set point resulted in 0.606 liters of leachate (9 mL per plant per day; that's less than a tablespoon), while the 17% treatment resulted in 16.65 liters of leachate (256 mL per day; a little less than a cup). Plants in the 17% treatment received 2.4 times as much water as those in the 14% treatment (33.0 versus 13.6 liters) without any beneficial effects. These data show clearly that automated irrigation control can greatly reduce both the amount of water that needs to be applied, as well as the leachate from the containers in nurseries. Similar results are expected for greenhouse production.

Some growers have expressed concerned about the lack of leaching and possible build-up of soluble salts in the substrate with this automated irrigation control. However, if leaching is necessary, growers can do this by choosing a longer irrigation duration.

In cooperation with Brower Electronics Laboratories, we have developed a simple irrigation controller which allows growers to determine the substrate water content at which plants will be watered, the duration of each irrigation, and a minimum interval between subsequent irrigations (to allow for water distribution in the containers). We expect that these probes can be interfaced with greenhouse computers in the near future as well.