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Early-season nitrogen increases growth, yield
By Robert H. Wells
Delta Research and Extension Center
STONEVILLE -- Research is proving what rice growers have suspected for years -- that a low rate of nitrogen applied to rice in the one- to three-leaf growth stage has a positive effect on production.
“Collaborative research in 2005 and 2006 with the University of Arkansas, Mississippi State University and the University of Missouri showed that rice plant height was increased by about 2 inches when 20 pounds of nitrogen per acre was applied to two-leaf rice,” said Tim Walker, assistant agronomist at MSU's Delta Research and Extension Center in Stoneville.
“Rice grain yield, when averaged across three preflood nitrogen rates, was greater when ammonium sulfate or when diammonium phosphate was applied as the early-season nitrogen source compared to when none was applied,” Walker said.
In addition to Walker, researchers from the Mississippi River Delta rice-growing region -- including Rick Norman of Arkansas and Brian Ottis of Missouri -- began the early-season nitrogen research as a way to quantify the true value received from the application, especially as the price of nitrogen has continued to increase.
“Growers, professional consultants, Extension personnel and scientists have often noticed that applying a relatively low rate of nitrogen to rice in the one- to three-leaf growth stage changes the appearance of rice,” Walker said. “Rice is often greener and more lush, and growers often say that they feel they flood this rice sooner than rice where no nitrogen has been applied.”
Researchers used ammonium sulfate, diammonium phosphate and urea as nitrogen sources in the study.
Walker said the data currently does not support the hypothesis that some of the early-season nitrogen may be counted toward the total nitrogen budget.
“The application should not be counted toward the total nitrogen budget because only about 10 percent of the 20 pounds of nitrogen applied at the one- to two-leaf stage is taken up by the plant,” Walker said. “Researchers will now try to identify methods to apply lower nitrogen rates and still achieve the same early-season growth benefits so that this application is more efficient.”
Growers' check-off dollars sponsored the early-season nitrogen research through the Mississippi Rice Promotion Board.
Rice production added nearly $118 million to Mississippi's economy in 2006.
Gibb Steele, a rice producer in Washington County for more than 30 years, said he sees a benefit from an early-season nitrogen application.
“It will get you to flood a little earlier, and it may save you some chemical applications,” Steele said.
Bill Killen, a rice consultant in the Mississippi Delta for 30 years, said he recommends an early-season nitrogen application on every acre he checks.
“We're trying to narrow that window down between the two- to three-leaf stage and the onset of tillering so we can go ahead and get a flood on the rice,” Killen said. “That's when herbicide costs start going down.”
For the early-season nitrogen study, researchers grew Cocodrie rice in each state on Sharkey clay soil each year.
When the rice reached an average of two leaves per plant, researchers applied 20 pounds of nitrogen per acre in the form of three different sources: ammonium sulfate, diammonium phosphate or urea. If a substantial rain did not come within three days after application, researchers flush-irrigated the plots to incorporate the nitrogen fertilizer.
When rice reached the five-leaf stage, researchers recorded plant height and total above-ground biomass and then applied three preflood nitrogen rates at 90, 120 and 150 pounds of nitrogen per acre.
Biomass was recorded again at boot-split, and grain yields were obtained at harvest maturity.
Researchers used biomass samples at five-leaf and at boot-split to analyze rice for nitrogen content and to determine total nitrogen uptake.