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Rice Under Pivot
Mechanized irrigation trial held on Arkansas farm

By Carroll Smith
Editor
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In the Mid-South, it’s not unusual to see center pivots dotting the landscape, watering large cotton and soybean fields. What is unusual is to see a center pivot walking across a rice field. It’s not a new concept, but often the net return from the field does not meet expectations. However, according to Valmont Irrigation, the company is starting its third year of research to identify and develop production guidelines to help farmers meet their economic expectations and have a secure, efficient and cost-saving alternative for growing rice under mechanized irrigation.

Bob Pollard, who farms rice and soybeans near Proctor, Ark., agreed to give the concept a try this year on about 65 to 70 net acres – a half quarter of a section minus the corners that a half circle pivot doesn’t water. He drill-seeded Clearfield XL 745 on the whole field.

“This hybrid probably is better suited for the center pivot because of its disease package,” Pollard says. “Also, Clearfield makes it easier to control the vegetation that flooded rice usually controls.”

Pollard points out that the idea behind watering rice under a pivot is that it will work in areas where either the ground is too uneven and levees would take up too much of the field or if you are limited in the amount of water you can pump because the water table is so low. Although farmers in Pollard’s area are close to the Mississippi River, water is not really an issue, but some producers do have ground that is not leveled, or they already have pivots they’ve been using to water cotton or soybeans and are interested in using the machinery to water a rotational crop, like rice, that will gross more money.

“The pivot approach makes harvest much easier because you don’t have to worry about the levees,” he adds. “Also, you can apply fertilizer and herbicides with a ground rig rather than an airplane. Just the application cost for applying fertilizer on this field aerially would have cost $30 per acre. So there’s a $30-per-acre savings right there.”

Pollard also notes that if you get your levees seeded early and get a good stand, you still lose at least 40 percent of yield that you would have had with regular paddy rice.

Tracks and wide tires
Although the concept of pivot-water rice is not new, it is still a learning experience to figure out just how much water you need with a center pivot to grow rice. Just this year, Valley monitored three sites: Pollard’s field in Arkansas, a full pivot in Kennett, Mo., and a full pivot in Charleston, Mo.

“Our schedule was to put a half inch on every two days when it didn’t rain,” Pollards says. “We used a half circle, which takes about 14 to 15 hours, because we didn’t know exactly what the timing and water requirements were going to be. I usually tried to run it at night to conserve a little more water.”

To prevent the pivot from making a deep track in the field, some of the tires were wrapped with tracks, which were wider than the tires, and a couple of towers were equipped with oversized tires. This precaution was taken because, according to Pollard, “After you make 15 trips or so in the heavier dirt that we have here, the pivot will begin to get stuck.”

Rice irrigation scheduling computer program
On the research side, Earl Vories, an engineer with USDA-ARS at the Delta Center in Missouri, worked with Valmont Irrigation’s Jake LaRue on irrigation scheduling.

“We had to know how much water rice uses,” Vories says. “We developed an adaptation of the Arkansas Irrigation Scheduler. It is a water balance scheduler, which means you keep track of how much water you have and try to estimate how much water the crop is using to keep it in balance all season long. We’re trying to determine the water usage of a pivot vs. flood irrigation because there is a trade-off on energy requirements. We are watching those numbers as well as using some soil moisture equipment that LaRue is working with. We were able to take the numbers we were getting from our equation and our program and compare them to the information that we were getting from out in the field. We will fine tune our program this winter so next year it will be more accurate for growing rice.

“This has been an unusual year,” Vories says. “With the rain we’ve been having, it’s hard to keep up with the moisture. Ideally, we’ll be getting more accurate every year. If center-pivot rice takes off, and we think it will, then there will be a version of the Arkansas Irrigation Scheduler, the Woodruff Method in Missouri or something that will allow you to schedule irrigations for rice the same way you do for cotton or soybeans.”

Water-mark sensors used as backup
LaRue says, “We didn’t want to rely on just one technique, particularly with the rainfall patterns we had. We needed a backup, so we used water-mark sensors to collect the data. We’ve got three stations: Two under the pivot at the seventh span and the fourth span, and we’ve also got one in the corner in the flood irrigation just so we can see what’s going on there. These water-mark sensors allow us to collect soil moisture data. We also put in telemetry monitoring so we can go online and see this.

“Bob would call me during the week to ask what the irrigation program and the soil moisture sensors are showing. The rainfall has been tricky in determining how much of it really contributed to our soil moisture. This is where the sensors came in handy. If the field is saturated, then an additional three inches doesn’t do us a bit of good because rice has such a shallow root system. I also walked the field and used a soil probe and field mapping just as a double check.”

At harvest time, in between the rains that plagued the area this fall, Pollard cut the pivot-irrigated rice field all in one day.

“I don’t know the exact yield at this point because we put the rice in the grain bin and haven’t hauled it out yet. But, from what the monitors indicated, the whole field averaged between 175 and 180 bushels dry weight,” he says. “Because of the different soil types, some parts of the field cut 200 bushels and some a little less than 170.”

When asked if he would try mechanized watering again, Pollard says, “Yes, I would. This has been interesting and a learning experience for me.”

Contact Carroll Smith at (901) 767-4020 or csmith@onegrower.com.

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