
In a small watershed in Iowa, hydrologist Michael
Burkart (left) and a farmer draw from a 30-foot-deep sampling well to test for
herbicides and nitrate. Click the image for additional information
about it.
Old Soil
Study Uncovers Value of Long-term Nitrate ResearchBy Luis Pons December 10, 2003An
Agricultural Research Service experiment
finished nearly 30 years ago--and uncovered recently during new study
preparations--shows that it's best to be patient when measuring the movement of
nitrates through soil and groundwater. Mark Tomer and Michael Burkart, both soil scientists and hydrologists at the
ARS National Soil Tilth Laboratory in Ames,
Iowa, found that nitrate applied during the experiment--conducted between 1969
and 1974--apparently took nearly 30 years to move through soils and reach a
70-foot-deep water table. This shows that water carrying nitrate can take decades to flow through a
watershed's soil subsurface to a stream and should be studied for longer
periods, according to the scientists, who work in the lab's Agricultural Land
and Watershed Management Research Unit. In the original study, conducted on a 74-acre field in western Iowa,
fertilizer was applied to soil at three times the normal rate. The resulting
soil nitrate concentration was tracked for the next decade. In 1996, Tomer and Burkart were preparing to monitor groundwater for a new
experiment when they detected the nitrate 60 feet deep in the soil. They
confirmed that the nitrate originated from the old experiment by examining
groundwater flow rates and ages, and by comparing the concentration's depth
with stream flow records. Leaching of nitrate from agricultural fertilizers has been linked to
concerns such as drinking-water quality and hypoxia, a condition in which water
bodies contain low oxygen amounts. Farmers are being encouraged to use nitrogen more efficiently, but resulting
environmental improvements have been difficult to document using studies
lasting just two to four years, according to Tomer. In summary, he adds,
application of a conservation practice within a watershed may take several
decades to fully effect improvements in groundwater quality. The results of this study were published in the November/December issue of
the Journal of Environmental
Quality, published by the American
Society of Agronomy, Crop Science Society
of America and the Soil Science Society of
America. ARS is the U.S. Department of
Agriculture's chief scientific research agency. U.S. Department of Agriculture |