Fitting Farming Practices to Minimize Water Pollution
By Ben Hardin
November 17, 2000
How much herbicide or fertilizer runs off farm fields to pollute
streams and rivers may depend less on the amount of the chemicals applied and
more on other factors such as soil characteristics, farming systems, and how
soon it rains after the chemicals are applied, according to studies by
Agricultural Research Service
For example, ARS scientists at
Columbia, Mo., found that
heavy rains that often fall on Midwest claypan soil soon after fertilizer
application may pose the greatest risk for nitrogen losses in the forms of
nitrate and ammonium. That's why, in the five-year study on the claypan soil
that is representative of 10 million acres, 75 percent of such losses occurred
within six weeks of application.
Fertilizer was also more susceptible to runoff when it was spread
evenly and then incorporated into the soil by tilling than when it was knifed
into the soil surface in narrow bands. And the herbicides atrazine and alachlor
were more prone to runoff in a no-till farming system than when they were
incorporated into the soil in a minimum-tillage system.
In another watershed study with different soil characteristics and
amounts of row cropping, the influences of agricultural chemicals on water
quality were nearly the opposite. The scientists found that herbicide
concentrations were much lower in streamwater from watersheds with soils having
good structure and pore space. However, nitrate concentrations were higher
because farmers in such watersheds typically rotate soybeans and corn and apply
more nitrogen fertilizer. Nitrate moves easily with percolating water heading
toward the stream.
The information from these studies could lead to development of
better management practices for specific farming regions to maximize the
potential for water quality improvements.
ARS is the chief scientific research agency of the
U.S. Department of Agriculture.
Scientific contact: Robert N. Lerch, ARS
Cropping Systems and Water
Quality Research Unit, Columbia, Mo., phone (573) 882-9489, fax (573)