In theory, a 58-acre rice field with straight levees would use about five inches less water with the automated early cascade irrigation shutoff or AECIS system compared to a conventional levee-gate cascade flood system.

That’s what Joe Massey and other scientists with the USDA-ARS Delta Water Management Research Unit who are developing AECIS believe would happen based on a model using 35 years of average rainfall data.

“The model suggests that we could expect a 16% water savings,” said Massey, speaking at the online Arkansas Soil and Water Education Conference. “This is using 35 years of rainfall data so it’s averaging across dry, normal and wet years with 31 inches for conventional cascade; 24 inches for multiple inlet rice irrigation or MIRI and about 26 inches for AECIS.”

Another projection from the model shows that AECIS could reduce the amount of runoff out of the sample field from 12 inches of water for the levee-gate cascade flood system to 6 inches for the automated early cascade irrigation shutoff system.

Alternate wetting and drying

Researchers would manage the bottom two rice paddies using the alternate wetting and drying or AWD technique that Massey helped develop while working as an agronomist at Mississippi State University.

“One of the key points of AWD rice flood management is that we know we need to hold the flood for at least 10 days after the initial application of nitrogen,” said Massey. “Waiting to draw down the flood depth also allows the canopy to close, helping with weed control. Another key aspect with AWD is we know that rice is particularly sensitive to water stress at early reproduction such as at green ring.”

Flood depth sensor

The research model is built on the 58-acre field with 10 paddies separated by straight levees and served by a 1200-gallon-per-minute irrigation well. The scientists “installed” a flood depth sensor in the eight paddy to notify the grower when the eighth paddy is full. They would also monitor the ninth and tenth paddies to make sure they had water in them but not to the point of runoff, if possible.

“The blue bars in this chart are the runoff estimates, and, again, that’s what the system would be trying to reduce,” said Massey. “And, in fact, we see that we get an estimated 50 % reduction if we use those lower two paddies as a catch basin, again adding water back at those critical times around early reproduction.”

The model predicts 12 inches of runoff from the cascade conventional system, six inches from AECIS and four inches with multiple inlet rice irrigation, which is designed to provide a more even distribution of water.

“The key question is what happens to the flood depth in the tenth paddy, and, in this particular model setting, we were targeting in a four-inch flood in that bottom paddy. So these are average paddy depths over an 85-day irrigation window or season. The cascade averaged 3.5 inches; MIRI, which does a little better job of maintaining the flood, 3.8 inches; and AECIS, an estimated 1.5 inches.

“In theory, according to the model, that’s enough to keep a standing flood on the field most of the time, but clearly there will be times when it could go down, and that’s why we need to field test this approach.”

To view the presentation, click on the 24th annual Arkansas Soil and Water Education Conference icon on www.arkswec.com.