Smart Irrigation Technologies: Water Savings Potential and Future Directions
By Michael D. Dukes, Ph.D., P.E., C.I.D., University of Florida / IFAS, Gainesville, Florida
In recent years, “smart” irrigation technologies have gained interest as a way to conserve water in landscape irrigation sys- tems while maintaining desired quality. These smart irrigation technologies consist of control technologies that apply irriga- tion according to estimated landscape needs based on meas- urements of parameters in the landscape (Fig. 1). Parameters measured in the landscape can consist of weather parameters that drive plant water use or soil water content that is influ- enced by plant water use. The Irrigation Association (IA) has
landscape. The exact method of this calculation varies de- pending on the particular manufacturer. There are generally three types of ET controllers: 1) signal based, 2) standalone, and 3) historical-based. The signal based controllers are sent an ET amount typically for the previous day. The “ET signal” is based on calculations performed using weather data in the region of the controller. This ET signal is then adjusted to represent water needs in terms of controller run time depend- ing on plant type, soil type, and other factors. Standalone controllers use some type of weather variable measurement to calculate ET. Again, adjustments are typically possible for the many variables encountered in the landscape. Finally, historical-based ET controllers use preprogrammed values of ET that are adjusted to onsite values based on temperature, for example.
Figure 1. Examples of soil moisture sensors (left) and evapotranspira- tion irrigation controllers (right).
been promoting Smart Water Application Technologies (SWAT) products for several years. The idea is that irrigation scheduling efficiency can be enhanced by using control systems such as evapotranspiration (ET) or soil moisture sen- sor (SMS) controllers rather just than a “dumb” time clock.
Soil Moisture Sensor (SMS) Irrigation Control Generally, SMS control can take two forms: 1) bypass
control and 2) on-demand control. In bypass control, the SMS controller is connected in line with a time clock. The SMS controller will then decide whether or not to allow the sched- uled time clock irrigation cycles. The SMS controller makes this decision by comparing the measured soil moisture content with an adjustable set point, which should be set just under the level where excess soil water percolation occurs. All of the SMS units we have tested use the bypass control method. On-demand control initiates and ceases irrigation within upper and lower soil moisture thresholds that are defined by the user is typically used larger commercial or institutional irrigation systems due to higher cost and more control options required.
Evapotranspiration (ET) Irrigation Control Evapotranspiration controllers in contrast to soil moisture controllers do not have sensors in the soil, but use weather variables to calculate the amount of water needed by the
Figure 2. Turfgrass plot experiment in Gainesville with 72 plots and St. Augustinegrass at the time of photo.
University of Florida, Institute of Food and Agricultural Sciences (UF-IFAS) Smart Controller Research
As a result of water supply pressures and commercial
availability of SWAT technology by 2003 a number of Florida local and state agencies as well as industry groups were inter- ested in testing the SWAT controllers under Florida conditions. Thus, the first research site established was in Gainesville at the Agricultural and Biological Engineering facilities. This test site consists of 72 independently irrigated turfgrass plots that are 12 ft X 12 ft and independently irrigated with spray heads (Fig. 2). The initial testing in Gainesville consisted of four SMS controller brands, each at three day of the week irrigation frequencies, 1 d/wk, 2 d/wk, and 7 d/wk. Comparisons included timer irrigation schedules as given by Dukes and Haman (2002) with and without expanding disk rain sensors as
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