MU Extension seeding rate trial looks at furrow-irrigated rice

Julie Harker

PORTAGEVILLE, MISSOURI

 Preliminary results from the first year of the University of Missouri Extension’s rice seeding rate trial are in.

“Our seeding rate trials are conducted at two research farms – the Missouri Rice Research Farm on a silt loam soil and the MU Lee Farm on a Sharkey clay soil,” said Justin Chlapecka, MU Extension rice specialist at the Fisher Delta Research, Extension and Education Center in Portageville.

“These represent the two predominant soils on which rice is grown in the Bootheel,” Chlapecka said. “We conduct these trials in flood-irrigated as well as furrow-irrigated systems, which is unique because I do not know of any other research in the U.S. that has looked as extensively at seeding rate in furrow-irrigated rice.”

Separate replicated trials are done in the top, middle and bottom thirds of the field to evaluate performance across the moisture gradient inherent in a furrow-irrigated rice field.

“Preliminary results from 2022 showed that a higher seeding rate was needed in the top and, usually, the middle thirds of the field,” said Chlapecka. “However, a seeding rate near or slightly lower than the typical recommended seeding rate was able to maximize yield potential at the bottom of the field, where conditions more like a flood-irrigated field are present.”

In a furrow-irrigated rice (FIR) field, the top third, closest to the poly-pipe or water inlet, is never underwater. The middle third is somewhat of a hybrid scenario, with maybe a little standing water but is mostly muddy. In the bottom third, standing water is usually held similarly to a conventionally flooded rice field.

“A FIR field is actually a continuous gradient, and the specifics depend upon the actual slope of the field and farmer preference,” Chlapecka said. “We are much more worried about different management considerations at the top half or so of the field where there’s no standing water and therefore aerobic conditions.”

The point of the trials on furrow-irrigated rice is to try to make yields closer to flooded rice, because, right now, “we generally tell folks to expect a 10% decrease in yield when comparing furrow-irrigated to flood-irrigated rice,” he said. A 10% decrease does not always occur, but producers should be prepared to accept that possibility.

Rice is a semiaquatic plant, meaning that it is adapted to grow in a shallow flood. Even in hybrid cultivars, which are generally better suited for an aerobic environment, moisture stress will occur in the absence of standing water. Aside from moisture stress, several nutrients are less available in a non-flooded environment, including nitrogen, phosphorus and, to a lesser extent, potassium. Nitrogen loss in furrow-irrigated rice can be a huge concern.

“I feel that altering our seeding rate has the potential to be one of many pieces in the puzzle of making up for the yield drag in furrow-irrigated rice,” said Chlapecka. “There will not be a one-step cure-all aside from pulling levees and putting a flood back on the field, which comes with its own issues.”

In 2023, planting date is being incorporated into flood-irrigated seeding rate trials. At both research stations, an early, normal and late-planted seeding rate trial will help researchers evaluate the need for altering seeding rate based on planting date. Currently, a 10%-20% increase in seeding rate is recommended when planting outside of the April-May planting window.

Rice seeding rate trials are funded by the Missouri Rice Research and Merchandising Council. Trials are anticipated to grow into three furrow-irrigated sites for 2023. Plans are to continue seeding rate trials indefinitely with new cultivar releases. ∆

JULIE HARKER: University of Missouri