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Can you cut seed rate without loss?

The introduction of patented traits in rice seed — like those in Clearfield and hybrid rice — has increased producers' seed costs. With the added expense comes a common question: can seeding rates be cut without sacrificing yield?

Someone has been checking. Until he was recently hired as Missouri Extension rice specialist, Brian Ottis was involved in a Stuttgart, Ark., study looking at seeding rates of XL8, CL 161 and Wells.

“We had seeding rates ranging from 15 to 120 pounds of seed per acre,” said Ottis at the annual Delta Center field day outside Portageville, Mo., on Aug. 31. “A typical drilled seed rate for a conventional crop is from 70 pounds to 120 pounds (2.2 bushels). Water-seeded rice rates go to 150 pounds and above. We wanted to see what our minimum cut-off would be on seeding rates. How low can we push the envelope?”

When the three varieties' yields were averaged over three years, XL8 did a “little better” than Wells. Clearfield 161 yields were significantly behind both XL8 and Wells.

“That wasn't earthshaking data — the hybrids tend to do a little better. The big thing we determined was that within any of those three varieties, seeding rates didn't matter with yield. We could plant a super-low seeding rate and still recover the yield we got with 120 pounds per acre.

“That's because rice grows a lot like wheat. It has the innate ability to produce many tillers to compensate for voids in the canopy. Rice's ability to do that is amazing.”

The key to the practice being successful is an even stand.

“If we have a low population density because of holes in the field, that's a different subject. But if we have an even stand at low densities, yields recover.”

A couple of decades ago, low seeding rates were frequently studied. But the last time it was looked at was in the late 1970s using old cultivars that may not have “produced the biomass or been as efficient as today's varieties.

“What we're finding is we can really push the planting envelope even with pure-line cultivars like Wells or Cheniere. This is especially true with semi-dwarfs. I think the semi-dwarfs produce more tillers than conventional varieties like Banks.”

The seeding rate studies will continue along with several other regional projects. One is the interaction of pre-flood nitrogen on seeding rates. Varieties being looked at: Cheniere, CL 131 and Wells.

“We want to know if we increase nitrogen with a low seeding rate will yields recover early. Can we keep the same amount of nitrogen and maintain the same yields?”

The work is important because of increasing nitrogen prices. “I've heard rumors that urea could reach $400 per ton. So we need to know how we can reduce input costs and maintain yield.”

Ottis and colleagues will also look at the impact of ammonium sulfate.

“Many growers tend to tinker with lower seeding rates. They've found that ammonium sulfate applied at one- or two-leaf rice tends to spur tillering a little earlier.

“Of course, that's a more expensive form of nitrogen. But if it helps recoup yields at low seeding rates, it may pay to use it.”

Drip-tape rice

Ottis is also working on a “somewhat revolutionary” project at the Marsh Farm near the Delta Center in Portageville: rice under sub-surface drip irrigation.

Admitting doubts at the study's outset, Ottis says drip-tape rice has shown promise. Using the tape has saved between 60 and 70 percent of normal water use.

The drip tape is buried 5 inches deep — “very shallow” — and runs off low pressure. Generally, drip irrigation for cotton can be buried 12 to 15 inches deep and is run under high pressure.

“The pressure on the rice system we're using is regulated by a 10-foot stand pipe. Water comes out of the riser from the well into the stand pipe with an 8-foot head on it. It acts like a toilet tank — a plastic ball that regulates water. Anyway, that provides the pressure for the drip system.”

The goal of the project is to see if there's an alternative for conventional flood practices. “If producers could use this in the Grand Prairie of Arkansas or southeast Texas it could solve some problems.”

Unfortunately, Bootheel water complicates the drip system. “We have to amend the water quite a bit with bleach and acid…One of the problems we've had is all the water in this area has a lot of iron. Because we have to put so much chlorine in the water, we tend to get accumulations of salt. If we don't get rains to bleach out the salt, we tend to see micronutrient deficiencies.”

All fertility needs can be delivered through the drip. There's no need for levees or an airplane. Everything can be done by ground-rig.

If the kinks can be worked out, drip-tape could open up rice production in areas now considered unsuitable for the crop.

“It has a lot of promise…By using the tape, we're saving a ton of water.”


A paper recently published in the Journal of Environmental Science and Technology also has Ottis' attention.

A research group from the United Kingdom “pulled seven rice samples from U.S. grocery stores. They found rice from the United States had more arsenic than rice grown in Bangladesh and India. However, the form of arsenic in the rice was organic, which is typically safer than the inorganic.”

Regardless, in an effort to get a handle on exactly what arsenic levels are, there's an effort among the U.S. rice-producing states to sample rice.

“They're especially interested in rice grown in fields with a cotton history, where some insecticides with arsenic may have been used over the last 50 years. They want to know if our rice definitely has more arsenic. We don't know the outcome, but we'd like to know if there are ‘hot spots.’”

The effort is also looking at whether there are varieties that exclude arsenic.

“Cocodrie, a popular variety, is a lot more susceptible to straighthead than Wells. We don't know if that's because Wells is better at metabolism than Cocodrie or if it's able to exclude arsenic. We hope to nail down the answers and breed varieties that exclude arsenic.”


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