Gravity is a wonderful thing, especially when it helps rice farmers flood their fields using conventional levee systems, a practice also known as cascade irrigation.

Although farmers and researchers have developed new water-saving techniques for irrigating rice, conventional levee-gate systems remain the preferred irrigation practice for many Midsouth rice producers.

A technique called Early Cascade Irrigation Shutoff (ECIS) promises to save these growers time and water by using a strategically placed water depth sensor to help them avoid over-pumping water onto their rice fields.

Examples of water-level sensors useful in triggering early cascade irrigation shutoff in levee-gate-irrigated rice fields, from left to right . (G. Payne, USDA-ARS)

Joe Massey with the USDA Agricultural Research Service’s Delta Water Management Research Unit in Jonesboro, Ark., and Drew Gholson of the National Center for Alluvial Aquifer Research in Stoneville, Miss., have tested the ECIS concept on commercial rice fields for several growing seasons.

“With ECIS a sensor is placed in a paddy above the last (i.e. lowest) paddy, and it is used to inform the producer when this upper paddy is full,” said Massey. “Runoff from the field is then captured in the last paddy, reducing water losses.”

Water savings

Massey and Gholson say field trial and modeling results suggest water savings of up to 25% are possible, when compared to fields in which the last paddy is filled or overfilled when the irrigation well cannot be shut off in a timely manner.

“This is on par with savings observed with side-inlet,” Massey said. “ECIS helps save time by eliminating guesswork and trips to the rice field as farmers seek to time irrigation shutoff so that the field is properly filled while not causing excessive runoff, as may occur when shutoff is delayed.”

Massey provided a photo depicting four examples of water-level sensors that could signal a farmer or the irrigation well that pumping was no longer needed to fill the paddy in which the sensor was installed.

Depending on a producer’s comfort level with the technology, ultrasonic sensors can be used in a variety of ways, he said. At the simplest configuration, when flood depth reached a preset level, the producer could travel to the field and manually shut off the well or switch it to another field.

“If the producer has also installed a pump controller on the well, he could remotely turn the well off using a phone application,” he noted. “Lastly, the sensor could be linked to the controller so that it automatically turns off the well when the target water depth is reached.

“A low-tech option is to use a manual flood depth gauge that provides a visible cue that the ECIS paddy is full. In some cases, these gauges can be placed so that they can be seen while driving down the highway or turnrow.”

MIRI practice

Some growers use side-inlet or multiple inlet rice irrigation, a practice developed for use on cascade or levee-irrigated rice by a farmer near Stuttgart, Ark., in 1990. MIRI enables a producer to fill each rice paddy through a series of holes punched in plastic irrigation tubing laid along the side of a rice field.

Adoption of MIRI has been slow, increasing by only about 1.4% per year over the last two decades. That is due to the extra time required to install polypipe and other issues associated with tubing, including twisting, rolling and blowouts.

Massey said not all rice fields will have sufficient irrigation capacity to benefit from ECIS. “In particular, fields served by irrigation wells providing less than 10 gallons per minute per acre delivery rate are not recommended for ECIS at this time, since over-pumping is less problematic in fields served by weak wells.

“Also, the rice field should be filled as per normal when the rice flood is first initiated. This helps to ensure that the last paddy will remain acceptably filled during the remainder of the irrigation season.”

By keeping a close watch on flood depths in the last paddy, a producer can determine the optimal flood depth in an upper paddy to use to trigger irrigation shutoff in cascade rice, he said. Massey and Gholson are actively seeking producers interested in testing the Early Cascade Irrigation Shutoff approach on their farms. Gholson can be reached at [email protected] and Massey at joseph,[email protected].