Agricultural News
Nitrous Oxide Could be Major Problem, But Grazing Could Help
Fri, 09 Apr 2010 17:39:15 CDTBiologists have long assumed that the farming of cattle and other livestock was part of the reason for rising nitrous oxide levels, because the animals' grazing disrupts the natural cycle that draws nitrogen into the soil. But nitrous oxide could be an even bigger problem. Scientists say nitrous oxide is about 300 times as powerful as CO2 at trapping heat in the atmosphere. According to new research published in Nature, in some places grazing actually reduces N2O emissions.
Steve Del Grosso, a soil scientist with USDA's Agricultural Research Service in Ft. Collins, Colorado, say's that's - quite surprising. The field research took place in Inner Mongolia, where frigid winters are followed by relatively balmy summers a cycle that turns out to be key. The study's co-author Klaus Butterbach-Bahl, says - Grazing is like mowing, it keeps the grasses short. When winter arrives, tall, ungrazed grasses trap the snow, forming an insulating blanket that keeps the soil below at a relatively warm 16°F or so.
On grazed land the snow just blows away, exposing the ground more or less directly to the chilly air and driving subsurface temperatures down to a few degrees below zero. At these temperatures, says Butterbach-Bahl, soil microbes some of which emit N2O can't easily survive. When the ground finally thaws in spring, the ungrazed grass not only has microbes ready to start churning out nitrous oxide, but also snowmelt to provide the water it needs to thrive. The scientist says - on grazing land, we see far less microbial activity.
These results would apply to about a third of the earth's grasslands, or about 20 percent of the land surface in temperate regions. But there's another caveat. Del Grosso says, - you can't look at grazing in isolation. It might reduce N2O emissions, but cattle and other livestock generate heat-trapping methane when they digest food. Grazing can also lead to soil erosion, and it can alter the ecosystems in other ways as well.
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