Economical pitless continuous-flow tailwater return system
helps maximize water-use efficiency in row rice.
• By Vicky Boyd,
University of Arkansas water management engineer Chris Henry developed and launched the Most Crop Per Drop Contest in 2018 to promote maximizing crop yields while minimizing water use. Since 2013, Henry had also been working at the Rice Research and Extension Center near Stuttgart, on a new economical, simple and easy to install continuous-flow tailwater return system to help growers improve water management on furrow-irrigated rice. Henry had just patented the system and was installing a handful of on-farm systems to test the system on working farms.
His presentation during a virtual 2021 winter production meeting caught the attention of Stephen Hoskyn, who farms with his family near Stuttgart, Arkansas.
Because they’re within the severely overdrafted Grand Prairie groundwater area, most of their farm had already been developed with reservoirs or tailwater return pits. But Hoskyn had picked up a new piece of ground that wasn’t tied in. Henry’s novel system would be ideal to put to the test in a row-rice field on the new farm. At the urging of Henry, Hoskyn also entered the field in the 2021 Most Crop Per Drop Contest.
How the system works
The continuous-flow tailwater system uses a high efficiency 2- to 5-horsepower variable-speed pump to move the water (500-900 gpm). It draws about the same amperage as a handheld hair drier.
A water-level sensor controls the motor speed — the lower the water level, the slower it runs.
Like other row water systems, a Computerized Hole Selection (aka Pipe Planner) program determines poly tubing diameter and hole sizes based on flow, field size and field slope.
Using a backhoe, an approximately 6-foot-deep sump is dug at the bottom of the field. A 5-foot metal pipe encases the sump with the below-grown portion solid metal. Only the few feet above ground is perforated.
The pump is installed in the sump and hooked up to the nearby electrical source. The pump is connected the top of the field using the higher pressure rated transfer tubing running through the middle of the field to relay water from the bottom to the top and feed it back into the row-watered poly tubing. Installation is fairly simple, and Henry thinks farmers could install the pumps themselves.
Hoskyn said he regularly watched the water level in the field. When it wasn’t flowing out of all the holes in the MIRI tubing, he’d turn on the well and run it for two to four days to top off the system. The actual irrigation set was based on temperature, rainfall and the needs of adjacent fields that used the same well.
Then he’d turn off the well and could go for up to eight days before restarting it, all the while the tailwater return system recirculated water.
For the 2022 season, Hoskyn plans to plant soybeans in the contest field. But he has an adjacent field, planted to soybeans in 2021, that he plans to rotate to row rice this season. He said he hoped to install a continuous-flow tailwater system in the new field.
Henry designed the system to be semi-portable. The sump is permanent, but growers can remove the pump and move it from field to field.
System vs. regular row-rice irrigation
What the tailwater system does is continuously recirculate water to improve crop uniformity and maintain near-field capacity top to bottom of the field, throughout the growing season, Henry said.
In a typical row-rice field, growers block the bottom of the field to catch and back up irrigation water. The top third or so receives irrigation every few days and dries out in between, potentially stressing the rice. The middle third is irrigated more like an alternate-wetting-drying — or AWD — field, while the bottom third is more like a conventional flooded rice field.
As a result, rice maturity in the top and bottom thirds is delayed, making harvest decisions difficult. But in the continuous-flow system the yields and moisture differences are much less from top to bottom. The system eliminates pigweeds and provides so much flexibility on scheduling water on the field compared to a field without the patented system.
Based on calculations, Henry said his system has about a two-year payback. In addition, it doesn’t take the large amount of acreage out of production that a permanent tailwater return pit does.
But the continuous-flow system won’t fit every situation, he said. The field must not have too steep a grade, must have an area at the bottom where water can be ponded for return, and can be installed feasibly within 3,000 feet of the power grid using small sized direct bury wire.
System put to the test
Based on the 2021 Most Crop Per Drop Contest results, Hoskyn took top honors with a water-use efficiency of 9.77 bushels per inch of water used. Water-use efficiency is calculated by dividing yield by the total water — rain plus irrigation — received by a field.
Hoskyn, who planted RiceTec’s XP753 hybrid, harvested nearly 240 bushels per acre corrected to 12% moisture. He applied 13.47 inches of irrigation and received another 16.09 inches of rain (adjusted) for 29.56 inches of total water applied.
As far as water-use efficiency, Hoskyn even beat Henry, who ran the continuous-flow tailwater return system on a 40-acre field of RT7321 at the RREC during the 2021 season.
“We look at basically everything every day during irrigation season,” Hoskyn said.
His feat also showed the importance of management, something Henry hoped the contest will reinforce.
“Technology is an aid — it’s the management that is most important,” Henry said. “Stephen had the technology, but he also watched the water. The last half of the season he was really watching his water use.”
Hoskyn said he had a hunch his field would do well, but taking top honors wasn’t a given.
“I was surprised that I won, but I knew we had good yield and didn’t use a lot of water,” he said.
What caught his attention more were the prizes for first place. Although Hoskyn said he was excited about the $11,000 worth of hybrid seed from RiceTec, he was also interested in the water management tools. Among those were an Irrometer manual reader and three Watermark sensors, a 10-inch McCrometer portable flow meter with an FS-100 Flow Straightener, a 10-inch Seametrics AG 90 Insertion Magmeter (flowmeter), a Trellis base and sensor station, a CropX soil moisture monitoring unit and an AquaTrac AgSense soil moisture monitoring unit, and cash from Delta Plastics.
“I’m pretty pumped up to play with the water sensors on some other row-rice fields,” Hoskyn said. “I’ve had a couple of different ones that people had given me to use over the years.”
Coming in second place was Seth Tucker of Monticello, who had a water-use efficiency of 6.31 bushels per inch. Third place went to Matthew Feilke of Stuttgart, with a water-use efficiency of 4.84 bushels per inch.
In previous Most Crop Per Drop contests, no row-rice field ever took first place, but were often second or third, Henry said. The Hoskins entry is the highest rice WUE ever achieved by anyone (8.7 bu-in was highest in 2020) in the four-year history of the contest. The top six row-rice entries averaged 215 bushels per acre with a water-use efficiency of 4.92 bushels per inch. Among the eight row-rice fields that entered the contest were the three winners.
To learn more about the Most Crop Per Drop Contest, visit https://bit.ly/3pUOaua.