Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 1996
Publication Date: N/A
Interpretive Summary: Contamination of groundwater resources by agricultural chemicals is a major concern of the agricultural community and the American public. Many of the reported cases of contamination have involved soil-applied herbicides used in corn and soybean production. The potential for these soil-applied herbicides to reach groundwater could be reduced if application rates were varied based on the organic matter content at each point in the field, instead of using the current standard practice of applying a uniform rate across an entire field. We previously developed a sensor which measures the amount of near infrared light reflected from the soil to estimate organic matter content and tested it with a representative set of Illinois soils. In this research, we evaluated the performance of the sensor with soils from across the U.S. and found that a single calibration could be used for a group of states with closely related temperature and moisture patterns, such as the lower Corn Belt (Ohio, Indiana, Illinois, Missouri, and Iowa). A multi-state range for a single sensor and calibration is advantageous as it would allow easier commercialization of the technology.
Technical Abstract: A previously developed prototype soil sensor which used near infrared (NIR) reflectance techniques was tested in the laboratory. The test set of soils included 30 Illinois soils and another 33 soils collected from across the continental U.S., all prepared at soil moisture tensions ranging from 1.5 MPa (wilting point) to 0.033 MPa (field capacity). As the geographic range erepresented by the included samples was increased, the predictions of organic carbon, cation exchange capacity, and soil moisture became less accurate. Calibrations obtained with soils from several states of the lower Corn Belt (Illinois, Missouri, Indiana, and Ohio) were only slightly less predictive of soil organic carbon than calibrations developed for the Illinois soils alone. Extension of the geographic range westward or northward from this area reduced the organic carbon prediction accuracy to an unacceptable level. Additional soils from the lower Corn Belt should be eanalyzed to ensure that acceptable predictions could be maintained for the range of agriculturally important soils present in each state.