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Highlights

Savings numbers in new studies across multiple soil types and climates are similar to those summarized in 2011 and are summarized here as 51% in research plot studies and 30% in single-family homes.

Abstract. Smart irrigation controllers, such as evapotranspiration (ET) and soil moisture sensor (SMS) controllers, have become commonly available from virtually all irrigation controller manufacturers. This review summarizes the literature since the Fifth Decennial National Irrigation Symposium (NIS) concerning these controllers in research studies and pilot implementations. Studies have expanded to multiple climates throughout the U.S. on a variety of soils and plant types. When these devices are implemented properly on sites that have potential irrigation savings (i.e., excess irrigation), they are able to reduce irrigation while maintaining plant quality. The level of reduction depends on many factors, including the amount of excess irrigation, climate, plant type, and human interaction with the technology. When studies report positive savings, the levels documented here range from 40% to 61% (51% avg.) in plot studies and from 28% to 32% (30% avg.) in residential studies. Of 17 identified studies in the past decade, five reported negative savings, and in most cases those results were due to ET controllers installed on sites with little excess irrigation or controller programming that was not optimized for savings. New trends in the industry include Wi-Fi signal-based ET controllers with smartphone app capability, an upcoming standard for SMS controllers, as well as smart controllers becoming mandatory in areas of the U.S. As identified in the Fifth Decennial NIS, it remains important to implement controllers on sites with the potential for irrigation reduction as well as proper implementation with the best current information. Finally, there is a need to understand human interaction with these devices because improper programming can make the difference between a water-saving device and ineffective technology with a dissatisfied customer.