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Nagging rice production questions

A decision three years ago to see Arkansas’ varied soils and climate conditions in a new light by creating three ecological study zones — Grand Prairie, Delta and White River — is allowing University of Arkansas Division of Agriculture researchers and extension specialists to offer highly targeted fertilizer, seed rate and herbicide recommendations.

Among the efforts being funded by Arkansas Rice Research and Promotion Board are:

Zinc-soil research

The Division hasn’t recommended zinc on heavy clay soils, mainly because zinc deficiency didn’t seem to be a major problem, says Nathan Slaton, UA associate professor of soil testing. But on occasion, he says, researchers find a zinc-deficient clay soil, typically in some precision graded fields.

His study also found a relationship between pH and zinc. He found higher pH in soils that test low in zinc.

Slaton said there’s a good enough relationship to justify recommending zinc application where deficiency could be a problem. That would only apply to a small percentage of clay soils, he noted.

Soil fertility

In the Delta zone, Rick Norman, UA professor of soil fertility, is working on a problem in some rice varieties grown east of Crowley’s Ridge.

“East of Crowley’s Ridge, it’s cooler, and the clay soils don’t have as much nitrogen as our silt loam soils west of the ridge. We noticed, especially with our semi-dwarfs, that they would come up and not really get any height by tillering stage.”

While seedlings of short stature rice varieties such as Wells were up to 8 inches tall, semi-dwarf seedlings east of Crowley’s Ridge on clay soils would be half that height.

Norman says researchers tried three forms of nitrogen fertilizer including urea, ammonium sulfate and DAP (diammonium phosphate). “The results were dramatic. Rice just jumped in height with all three treatments, but especially with DAP, and it looked better,” he says. And researchers found they could flood the semi-dwarf rice a week earlier.

Nitrogen availability

Jeremy Ross, soybean specialist with the UA Cooperative Extension Service, Norman, Slaton and Chuck Wilson, UA rice specialist, are testing three promising methods for a soil nitrogen test to predict how much nitrogen is available during the season for a crop. Researchers nationwide have been looking at the problem for more than 50 years.

“Laboratory incubation studies indicate that all three methods show great promise in the field. These are all simple-to-use methods,” says Norman.

If the experiment works, Norman says, the university will be able to fine-tune recommendations and make them more accurate to help farmers avoid wasting costly nitrogen fertilizer.

Phosphorus-potassium deficits

Other studies in the ecozones are showing that as rice yields have increased dramatically, more phosphorus and potassium are being removed from soil. “At some point, growers will have problems,” Slaton says.

In the White River and Grand Prairie ecological zones, “99.9 percent of the time when there are deficiencies, they occur on silt and sandy loam soils,” says Slaton.

“In the early 1990s, we thought that if you applied it strictly to your soybeans, you were doing all you needed to do. When we changed our recommendations to include phosphorus fertilizer on rice, we built our soils back up to an adequate level.”

Over time, farmers have also reduced potassium availability in some soils, suggesting that potassium fertilizer is needed. However, Slaton says more work is needed before he suggests changing the university’s potassium fertilizer recommendations.


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