By Robert H. Wells
Delta Research and Extension Center
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.