Rice irrigation termination program

A computer program on rice irrigation termination soon may be headed to your monitor. Much like COTMAN in cotton, the program should provide rice farmers a tool to save valuable moisture and, in the end, money.

When it is released, the finished product will have been fed the sweat of many researchers, built upon foundations constructed long ago.

“We just keep plugging away at it,” says Paul Counce, “and we’re getting close to having a nice tool for rice farmers.”

Building the program

It’s been known for several decades that great water savings can be had by draining rice as early as possible without reducing yield or milling quality. “I came to Arkansas over 22 years ago, and scientists here had already established that,” says Counce, rice physiologist at the Rice Research and Extension Center in Stuttgart, Ark. “The way had been paved.”

Still, there were gaps in knowledge. “The early studies didn’t measure head rice yields. We needed that data. So, in cooperation with Earl Vories (an agricultural engineer at the Northeast Research and Extension Center in Keiser, Ark.) and Terry Siebenmorgen (a food scientist with the University of Arkansas in Fayetteville, Ark.) we conducted studies over four years.”

Rice test fields were drained at 50 percent heading (when half the panicles have emerged) and then two weeks and four weeks after. When drained at 50 percent heading, rough rice and head rice yields were reduced in more than one location. However, there were no yield reductions when draining at two weeks after 50 percent heading.

When this information was published in the early 1990s, draining recommendations for Arkansas and Mississippi rice changed.

The growth stage system

Since then, Counce and colleagues have developed a growth staging system for rice. “We needed to get some rules in place,” says Counce, who spoke at the RREC field day on Aug. 11. “This helps in all manner of ways: making hail-damage claims, applying chemicals, knowing when cool temperature damage could occur.

“For example, grain at R5, when held up to the light, is seen expanding inside the hull. At R6, the grain is gaining in thickness. At R7, at least one grain on the main stem panicle has turned yellow. At R8, at least one grain on the main stem head has turned brown. At R9, all grains that have reached R6 have brown hulls. The growth stages follow DD50s — this new finding will allow us to do timing work we’ve not done before.”

Using the growth stages

With rice — as with grain sorghum and corn — a water deficit before grain is filled reduces yield and quality.

“In the greenhouse, we would induce drought stress at different growth stages,” says Counce. “Anytime before R9, we reduced yield. We also studied water use by the rice crop. At growth stage R3 the crop uses about 0.25 inch of water daily. Researchers have found that at stage R8, rice will use about 0.06 inch every day. Rice at developmental stages after R6 just isn’t using much water.”

In addition, a rice crop uses less water after the flood is removed. In their calculations, though, the researchers overestimate water use to insure the crop doesn’t run out of moisture.

“Old NRCS soil surveys tell us how much water different soils will hold. Rice, unlike cotton or soybeans, can use water between field capacity and saturation. The numbers tell us how much water is available after a rice crop is drained.”

From that, Counce calculates water use at different growth stages, beginning with mature rice and working backwards. That way, he can answer questions like, “When rice is at R7, how much water will it take to finish the crop?”

Whenever the amount needed in a certain growth stage is less than or equal to the amount of water the soil holds when drained, there’s enough water in the soil profile to take the crop safely to maturity.

“We’re trying to take this to farmers,” says Counce. “We’re talking to farmers to get input. I’d really like to see this available to all rice farmers. Right now, though, it’s still a science program.”

Is there potential for this to be for rice what COTMAN is to cotton?

“Yes. This gives us a new way to approach the rice crop. It sets the zero on the DD50. I hope this will be available as a computer program within the next few years.”

The bottom line

Understandably, the bottom line is what everyone is curious about. By using the termination program, economists say, farmers can save as much as $23 per acre.

“You can save that much just by taking water off at the right time,” says Counce. “Of course, if someone is pumping from a full aquifer that’s 12 feet deep, the savings will be less dramatic. In areas like the (Arkansas) Grand Prairie, where water is often very deep, savings would be substantial.”

Producers want to use only as much water as is necessary to fill the crop. “In many cases, soybean irrigation takes a backseat to rice. A producer will water his rice before soybeans every time. This system would help a farmer know when soybeans can get the water without worrying about rice.”

Counce says there has been “much positive response” from farmers learning about the program. “We need to test it some more, but everyone I speak with seems excited.”

He sees many uses for the program. “One seed grower with zero-grade rice says the key to his system is keeping out red rice. He’s needs to know when he can drain safely so he doesn’t bury red rice when harvesting. Red rice pressed into wet soil will sit there waiting for the next season. This will help in his situation.

“I have heard it can cost $25 per acre to repair ruts. If you make ruts, you’re out of no-till systems. This would help maintain those systems, too.”

e-mail: [email protected]

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.