An agricultural experiment concluded nearly 30 years ago is still influencing concentrations of nitrate in ground water and stream flow draining from a 74-acre field in western Iowa, according to scientists at the National Soil Tilth Laboratory, Ames, Iowa.
"Scientists are trained to study agricultural practices over several years to obtain conclusive data on how agricultural production is affected, but we are realizing the environmental effects of those practices take even longer to assess. The benefits of improved practices may take many years to be fully understood and realized," says Mark Tomer a scientist with the USDA Agricultural Research Service.
In an experiment conducted from 1969-1974, triple-rate fertilizer applications were made on a field forming the watershed for a small stream in western Iowa. The movement of a large pulse of nitrate into the deep soils was tracked in follow-up studies, conducted up to 10 years later. But years later, scientists were surprised when they detected evidence of the same pulse of nitrate at a 60-foot depth when setting up to monitor ground water at the site in 1996.
"We were initiating a new cropping-systems experiment, not attempting to follow up the old research," says Tomer. "The scientists who began the original experiment in 1969 have already retired."
In order to confirm the deep nitrate could originate from the old experiment, ground water flow rates and ages were investigated. The movement of the
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Contact: Sara Uttech
suttech@agronomy.org
608-273-8080
American Society of Agronomy
10-Dec-2003