Conservation tillageplanting crops in stalks
or other residue of a previous cropdecreases soil's emission of carbon
dioxide. But without the right fertilizer practices, conservation tillage can
increase emissions of nitrous oxide, a gas with 300 times the greenhouse
potency of CO2. Click the image for more information about
More about No-Till and Greenhouse Gas
Emissions By Don
Comis November 25, 2005
The type of fertilizer used, and the manner in which it is applied,
can make or break reduced tillage's ability to control greenhouse gases,
Agricultural Research Service (ARS)
No-till and reduced tillage are promoted as a way farmers can reduce
greenhouse gas concentrations in the atmosphere by storing more carbon in soil.
But there has been limited information on how tillage or other farm practices
affect soil emissions of greenhouse gases other than carbon dioxide.
A study conducted by ARS soil scientist
Venterea on the effects of long-term tillage techniques and fertilizer
practices has shown that, if not done with care, reduced tillage practices can
increase emissions of more powerful greenhouse gases, particularly nitrous
oxide. At 300 times the strength of carbon dioxide, nitrous oxide can easily
offset the benefit of carbon dioxide reduction. Venterea works at the ARS
and Water Management Unit in St. Paul, Minn.
Farm fields are the biggest source of nitrous oxide emissions in the
United States, with up to one-third of the agricultural emissions coming from
farms in the north central region of the country.
Venterea and colleagues have shown that farmers using no-till should
inject nitrogen fertilizer more than 4 inches below the soil surface, beneath
the layer of soil that is most conducive to nitrous oxide production.
In field tests, Venterea and his colleagues compared the nitrous oxide
emissions from three different tillage systems in combination with anhydrous
ammonia, urea nitrogen fertilizer pellets, or liquid urea ammonium nitrate.
Anhydrous ammonia caused about double the losses of nitrous oxide than
the other two fertilizers. But combining no-till with anhydrous ammonia
injected 6 to 8 inches deep emitted the least nitrous oxide of the three
tillage-anhydrous ammonia combinations tested.
In contrast, spreading urea nitrogen fertilizer pellets on a field's
surface caused higher nitrous oxide emissions under no-till compared to more
intense tillage. Tillage had no effect on emissions when liquid urea ammonium
nitrate was applied to the surface.
Venterea conducted the studies in southeastern Minnesota from 2003 to
2004, using soil chambers to capture nitrous oxide emissions.
The research was published in the
Journal of Environmental Quality.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.