Rice, one of the most versatile foods, is the
foundation of many dishes, including rice pudding, rice cakes, beans and rice,
and fried rice. So, it's no wonder that world rice production is 384 million
tons. Rice is the primary food for about 50 percent of the world's population.
It may also have a major impact on global warming by contributing to the
emission of an important greenhouse gas: methane.
"Rice is a plant that grows best in wet soil, with its roots
flooded," says L. Hartwell Allen. "But flooded rice crops emit
substantial amounts of methane to the atmosphere, especially when fresh organic
matterlike plant residuesis added back to the soil." Allen is
a soil scientist in ARS' Crop Genetics
and Environmental Research Unit in Gainesville, Florida.
Methane is a gas that contributes to the greenhouse effect, having a 20-fold
greater global warming potential than carbon dioxide (CO2). Some
studies show that up to 20 percent of global methane emissions come from
flooded rice fields.
For the past few years, Allen and colleague Jeff T. Baker, now with ARS' Remote
Sensing and Modeling Laboratory in Beltsville, Maryland, have studied the
effects of global change on flooded rice and found that rice could stand a
little drying out.
In a recent study, they simulated potential global change
conditionsincreased drought and rising CO2by growing
rice plants in special outdoor chambers. The studies showed that rice yields
drop when the plants are grown during short, 2-week droughts occurring when
plants flower. However, when the researchers doubled CO2 levels by
injecting the gas into the chambers, the plants maintained yield while using
less water and enduring a longer drought period.
Allen and Baker also recently discovered that periodically draining the soil to
aerate roots with atmospheric oxygen drastically decreases methane emissions.
"This may be an easy on-farm practice that would help manage methane
emissions," says Allen.
"Our research shows that reducing methane emissions from rice fields is
important in helping to reduce or prevent the contribution of rice to global
warming," notes Allen. "Since the United States produces only a small
fraction of the world's rice, this water management practice needs to be tested
and applied more internationally, especially in Asia."By
Weaver-Missick, Agricultural Research Service Information Staff.
L. Hartwell Allen is in the USDA-ARS
Crop Genetics and Environmental Research Unit,
Bldg. 350, Agronomy Physiology Laboratory, Gainesville, FL 32611; phone
(352) 392-6180, fax (352) 392-6139.
"Reducing Methane Emissions From Rice" was published
in the May
2000 issue of Agricultural Research magazine.