Sensing the Soil’s Depth Cuts Fertilizer Use--and Pollution Risk

U.S. Department of Agriculture scientists are helping Midwest corn farmers take the guesswork out of using nitrogen fertilizer. Preliminary results of a two-year field study on Midwest claypan soil showed that farmers can maintain good crop yields and still reduce both the use of fertilizer and the risk of groundwater contamination.

Farmers usually apply nitrogen fertilizer for the best crop yield based on a field’s past history and its average soil condition. Once the equipment is readied, they spread the fertilizer at a single rate over the entire field. The problem with this practice is that all of the soil in one field isn’t the same. Soil quality varies from one point to another within a field.

To measure this variability, scientists with USDA’s Agricultural Research Service in Columbia, Mo., tested an electromagnetic conductivity sensor on 300 acres of claypan soil in north central Missouri. The sensor allowed the scientists to measure the topsoil depth--a key factor that controls production on claypan soils. The more topsoil, the more productive the soil is because of the soil’s increased water-holding capacity.

The scientists began using the sensor in 1992 and two years later hooked it to a global positioning system receiver and laptop computer. Using the data from the automated system and sensor, the scientists applied the same amount of nitrogen fertilizer that a producer normally would use, but they redistributed the fertilizer to areas in the field where it was most needed.

Some portions of the field got less than the conventional rate of nitrogen fertilizer and others got more. Where less fertilizer was applied, the corn crop was more efficient in its nitrogen use and yields were the same as with the conventional rate. In areas where it was deemed necessary to add more, yields averaged 10 bushels more per acre.

Scientific contact: Kenneth A. Sudduth, ARS-USDA, Cropping Systems and Water Quality Research Unit, University of Missouri, Columbia, MO (573) 882-4090; kenneth_sudduth@muccmail.missouri.edu; or Newell R. Kitchen, ARS-USDA Cropping Systems and Water Quality Research Unit, University of Missouri, Columbia, MO (573) 882-1135; newell_kitchen@muccmail.missouri.edu.