June 8, 2004,
ARS News Service: Although cattle add some
nitrogen to pastures via their feces and urine, it isn't
enough to warrant removing them from a pasture, according
to an Agricultural Research Service scientist, even
if the pasture is above groundwater contaminated by
high levels of nitrate-nitrogen.
A study by Lloyd Owens, a soil scientist at the ARS
North Appalachian Experimental Watershed Laboratory
in Coshocton, Ohio, has shown that it doesn't make any
difference in groundwater nitrate levels whether cattle
are on the pasture or not.
What does make a difference is fertilization. Pastures
with high nitrate levels can't be fertilized for at
least a few years, until the levels drop sufficiently.
U.S. Environmental Protection Agency guidelines for
drinking water stipulate 10 parts per million (ppm)
nitrate-nitrogen as the maximum allowable safe level
for drinking water.
Owens studied problem pastures with groundwater nitrate-nitrogen
levels of 13 to 26 ppm, caused by heavy experimental
fertilization for 11 years before the study. He stopped
fertilizing for a seven-year study to see if that would
bring nitrate levels down to safe levels. For comparison,
he let cattle graze on two pastures, and fenced them
out and made hay from two other pastures.
In the groundwater underneath three pastures, the nitrate-nitrogen
levels dropped below 10 ppm within three years; after
five years, the levels below all four pastures fell
to 2 to 4 ppm.
Because of soil conditions, some fields are more prone
to high nitrate levels. Fertilizing every year can eventually
turn them into problem fields. The finding is good news
for farmers because they don't have to remove cattle
from these problem fields, as long as they stop fertilizing
for a while. Letting cattle graze saves the time and
labor of baling hay for feed, which is what was done
on the two test pastures where cattle couldn't graze.
The withholding of fertilizer caused only a slight
decrease in grass growth, so it doesn't seem to be a
serious disadvantage to farmers, especially compared
to the environmental benefit.
More information about nitrate research can be found
in the current issue of Agricultural Research magazine,
online at: http://www.ars.usda.gov/is/AR/archive/jun04/nitrate0604.htm