Sensors Used to Reduce Nitrogen Fertilizer Application

Results could have positive environmental effects for Gulf of Mexico. Compiled by staff

Published on: May 16, 2005

Using the right amount of nitrogen fertilizer to obtain desired corn yields can be a challenge for both economic and environmental reasons. Applying too much nitrogen is costly and can contribute to water quality problems. Applying too little can result in sub-par crop yields. Now, researchers at the University of Missouri-Columbia are using sensors called light emitting diodes (LEDs) to accurately measure the color of young corn and apply variable rates of nitrogen according to plant needs.

"The key is that all fields will have an in-field variability, which is illustrated by the color of the corn itself," says Harlan Palm, research assistant professor of agronomy in MU's College of Agriculture, Food and Natural Resources.

The researchers are in their second year of testing this new technology on farms across Missouri. They hope this LED approach will not only increase profits for producers, but also create a healthier environment, including in the Gulf of Mexico, where nitrogen runoff carried by the Mississippi River has created a "dead zone."

Dead zones happen when nutrients such as nitrates and organic nitrogen promote rapid growth of tiny plankton in coastal waters, which then decay and consume oxygen. The low oxygen level in the water is called hypoxia. Hypoxia stresses or kills bottom-dwelling creatures on which the region's seafood industry depends.

"Past research has shown that many fields in Missouri can make full yields with less nitrogen than they are receiving," adds Peter Scharf, MU nutrient management specialist.

In the study, researchers applied an ample amount of nitrogen in early spring to only one area of the field. LED devices mounted on a fertilizer applicator measure light reflected from small (12- to 15-inch) corn plants in this area, providing a reference or baseline point. The computer-equipped applicator then applies nitrogen fertilizer to the rest of the field. Variable rates of nitrogen are applied to the crop depending on the color or reflective value of corn leaves detected by the LEDs.

"The idea is to cut back in smart places," Scharf says. "This technology allows us to diagnose how much fertilizer is needed better than we could with a previously used method."

The Environmental Protection Agency has adopted an action plan based on voluntary programs to reduce nitrogen loading in the Mississippi River. Their target is reducing the size of the hypoxic zone to a five-year average of less than 5,000 square kilometers. In recent years, the hypoxic zone has been as large as 20,000 square kilometers.