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By the U of A System Division of AgricultureDec. 3, 2018
Download MS Word version
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Research article available online: Nitrogen Source Effects on Methane Emissions From Drill-Seeded, Delayed-Flood Rice
FAYETTEVILLE, Ark. — University of Arkansas System Division of Agriculture research
in rice may lead to more sustainable crop production in Arkansas and around the world.
The quest for increased sustainability in agriculture and other industries includes examining
greenhouse gases and how they’re generated. In the U.S., only a small fraction of
greenhouse gases are attributed to agriculture – 8.6 percent, according to the Environmental
Protection Agency. Within that small fraction, rice production is classed as a minor
methane source. Nevertheless, greenhouse gas emissions, however small, may have an
economic impact on Ag industries at some point in the future.
“Tackling large-scale problems often takes a one-step-at-a-time approach,” said Jean-Francois
Meullenet, head of the Arkansas Agricultural Experiment Station, the research arm
of the Division of Agriculture. “Research our faculty is conducting, including Dr.
Brye’s important body of work in rice, is part of a broader effort to increase agricultural
productivity for our farmers, both short- and long-term, while also increasing agriculture’s
With the number of acres of rice grown globally, these small steps can lead to bigger
impacts, Meullenet said.
After years of field research, quantifying many of the variables that affect production
of methane during rice production, Kris Brye, professor of applied soil physics and
pedology in the department of crop, soil, and environmental sciences for the Division
of Agriculture and the University of Arkansas’ Dale Bumpers College of Agricultural,
Food and Life Sciences, said he has generated the most comprehensive, replicated,
plot-scale data set on the subject for Arkansas.
Research conducted by former Bumpers College graduate student Chris Rogers and current
Division of Agriculture research associate Alden Smartt, has shown that choice of
nitrogen fertilizer can affect the amount of methane emitted from Arkansas rice fields.
Rogers is now an assistant professor at the University of Idaho’s Aberdeen Research
and Extension Center.
Role of methanogens
Brye said that methane is produced in rice fields because the fields are flooded for
most of the growing season. “Under flood, the soil becomes reduced to an anaerobic
state,” he said. “Basically, the soil loses most of its oxygen content.”
The lack of oxygen in the soil spurs a group of microorganisms called methanogens
to feed on carbon and produce methane, Smartt said.
Brye said the floodwater acts as a cap on the soil, containing the methane in the
ground. However, the gas escapes by at least two common means. From time to time,
someone has to walk through a flooded rice field.
“Sometimes you take a step and a bubble of gas burps out of the ground,” Brye said.
“That’s methane escaping because the soil was disturbed.”
Soil burps aside, the main avenue for methane escape is through the rice plant, Brye
said. The gas is passively taken up by the roots, transported upward through the plant
tissues and emitted into the air.
Brye said many factors affect the volume of methane emitted. Silt loam soils have
coarser particle and pore sizes than clay soils, enabling easier transport of the
gas to the surface. The loamy soils also promote more microbial activity, emitting
more methane than plots in finer-grained clay soils.
The type of rice grown also matters. For example, hybrid rice varieities that generally
have higher yields, more biomass and denser root systems than conventional varieties,
have more metabolic activity. This leads to more oxygen in the flooded soil, which
slows methanogen activity.
Role of fertilizers
Some fertilizers add carbon to the soil, feeding hungry methanogens and spurring higher
methane production and emission in some soils, Brye said.
Part of the research Rogers conducted during his Ph.D. program compared three nitrogen
fertilizers — pelletized poultry litter, with high carbon content; urea, with moderate
carbon content; and ammonium sulfate, which has no carbon.
As expected, fields fertilized with ammonium sulfate emitted significantly less methane
than urea or pelletized poultry litter. The difference in methane emission made by
fertilizer choice was significantly greater in silt loam soils than in clay soils,
“Clearly, choice of fertilizer nitrogen source, especially ammonium sulfate in silt
loam soils, has the potential to significantly mitigate methane emissions from Arkansas
rice fields,” Brye said.
The downside is that ammonium sulfate is more expensive than urea, the standard nitrogen
source used in rice production, and producers aren’t likely to be able to afford its
use as the sole source of nitrogen.
Brye’s reseach continues to examine how rice management practices such as tillage,
urease inhibitors and irrigation systems interact and influence the production of
methane and other greenhouse gases. Understanding these interactions is needed to
assess which farming practices generate the least greenhouse gas.
The results of the research were reported in “Nitrogen Source Effects on Methane Emissions
from Drill-Seeded, Delayed-Flood Rice Production,” a paper published in the January
2017 issue of Soil Scienceby Rogers, Smartt, Brye and Richard J. Norman, professor of soil fertility in the
department of crop, soil and environmental sciences.
To learn more about Division of Agriculture research, visit the Arkansas Agricultural
Experiment Station website: https://aaes.uark.edu. Follow us on Twitter at @ArkAgResearch.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen
agriculture, communities, and families by connecting trusted research to the adoption
of best practices. Through the Agricultural Experiment Station and the Cooperative
Extension Service, the Division of Agriculture conducts research and extension work
within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas
System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.
The University of Arkansas System Division of Agriculture offers all its Extension
and Research programs to all eligible persons without regard to race, color, sex,
gender identity, sexual orientation, national origin, religion, age, disability, marital
or veteran status, genetic information, or any other legally protected status, and
is an Affirmative Action/Equal Opportunity Employer.
Media Contact: Fred MillerU of A Division of AgricultureArkansas Agricultural Experiment Station(479) firstname.lastname@example.org