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Title: REAL-TIME SOIL AND CROP SENSORS - HOW WELL DO THEY WORK?

Author
item Hummel, John
item Sudduth, Kenneth - Ken
item BIRRELL, STUART - UNIV OF MISSOURI

Submitted to: Book Chapter in Special Publication 1194 New Trends in Farm Machinery Devel
Publication Type: Book / Chapter
Publication Acceptance Date: 7/3/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Site-specific crop management is a technique in which the application rates of such inputs as herbicides and fertilizers are varied within a field due to point-to-point differences in soil and crop related properties. For efficient operation, automated instruments are needed to measure these differences in the field. We report in this paper on sensors for soil properties such as soil organic matter, soil moisture, and soil nutrients, and a sensor to measure the depth to dense clay layers that inhibit moisture movement and root growth. Accurate sensors are important components in a system to optimize inputs to match crop needs that could lead to improved profitability and reduced leaching and environmental impact.

Technical Abstract: Development of sensors, particularly sensors specifically developed for Site Specific Crop Management, currently lags the other enabling technologies. Real-time sensors, i.e., those that can sense a soil or plant parameter and produce an estimate of the value of the parameter within a few seconds, are under development. Our research has exploited two technologies - spectral reflectance and ion-selective membranes, for sensing of soil parameters. We found that optical estimation of soil organic matter (SOM) and soil moisture content can be accomplished with wide-band and narrow band spectral reflectance data. A rugged portable NIR sensor was developed which was able to predict SOM (r2 = 0.89, SEP = 0.40% SOM) and soil moisture (r2 = 0.94, SEP = 1.88%). A system using ion-selective membranes, field effect transistors, and flow injection analysis was able to predict soil nitrates in manual soil extracts with correlation coefficients greater than 0.9. Research on the sensors for crop parameters has included the use of a light source and photodiodes to measure grain flow rate on a combine. A spring-loaded rod attached to a rotary potentiometer, was shown to count corn plants at harvest with errors in the 5% to 10% range. Preliminary results with a photoelectric sensor appears to have comparable accuracies, while also providing a measure of plant stem diameter.