Sensing the Soils Depth Cuts
Fertilizer Use--and Pollution Risk
By Linda Cooke
July 8, 1997
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
Farmers usually apply nitrogen fertilizer for the best crop yield based on a
fields 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 isnt the
same. Soil quality varies from one point to another within a field.
To measure this variability, scientists with USDAs
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
soils 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;
or Newell R. Kitchen, ARS-USDA Cropping Systems and Water Quality Research
Unit, University of Missouri, Columbia,
MO (573) 882-1135; firstname.lastname@example.org.