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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #103792


item Sudduth, Kenneth - Ken

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Other
Publication Acceptance Date: 7/22/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Variable rate application of granular fertilizer is a common practice in precision agriculture. Many granular materials are applied with air spreader machines, where the fertilizer is injected into an airstream, travels through a flexible tube, and is then dispersed onto the ground along the swath of the applicator. Currently, the fertilizer rate applied with air spreaders is estimated by measuring the rotational speed of the fertilizer metering wheel and assuming a known quantity of fertilizer per revolution. More accurate measurement and control of fertilizer delivery could be accomplished if the actual flow rate of the material was measured. In this project we designed, constructed, and tested an optical sensor to measure the flow rate of fertilizer suspended in an air stream. This sensor system combined commercially available optical and electronic components with novel data processing approaches. The sensor was able to measure the flow rate of several granular fertilizers very accurately in laboratory tests, although product-specific calibrations were required for maximum accuracy. Other tests showed that the sensor could respond well to variations in fertilizer flow, as would be encountered in variable rate applications. This research will benefit scientists and engineers by providing them with a new tool to accurately measure fertilizer flow rates in variable rate air delivery systems. If commercialized, it will also benefit users of variable rate systems (farmers and agribusiness) by providing them with sensors that could improve the accuracy of application equipment.

Technical Abstract: An optical sensor to measure granular fertilizer flow in an air stream was designed, built, and laboratory tested. The sensor components included a laser line generator that transmitted light across a trapezoidal chamber to two 16-element photodiode arrays. The air suspended granules would break the light causing a count to be recorded. The counts were translated into a mass flow rate. Static tests of five materials and six mass flow rates were performed in a replicated block design. Dynamic tests of one material with six step changes in mass flow rate were performed. Results of the static tests showed a strong linear relationship between sensor output and mass flow rate that was repeatable. Static test confidence interval analysis (p = 0.05) showed evidence that the sensor system needs to be calibrated for different products. Dynamic test results showed the sensor followed the step changes in mass flow rate fairly well but indicated limitations in the present data analysis algorithm. The sensor system showed potential as a first step to a real-time granular fertilizer sensor.