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Evaluation of a Variable Rate Application System for Site-Specific Weed Management

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  051120,  2005 ASAE Annual Meeting . (doi: 10.13031/2013.18863) @2005
Authors:   Jeffrey W. Vogel, Robert E. Wolf, J. Anita Dille
Keywords:   Variable rate application, precision agriculture, spatial weed management

The objective of this study was to evaluate the ability of a conventional spray system adapted for VRA to successfully apply herbicides in a site-specific manner. A tractor mounted, VRA spraying system was constructed with commercially available equipment during the spring of 2003. The sprayer was equipped with 568 L tank and a 7.6 m boom with Spraying Systems Turbo TeeJet 11002, 11003, and 11004 nozzles mounted on 15, three-position nozzle bodies spaced 51 cm. The sprayer controller was a Raven SCS 440 with serial interface. To attain automatic product shutoff, the controller used a fast-close control valve placed on the 2.5 cm main product line located after the flow meter. A sprayermounted radar was used to monitor speed. A Trimble AgGPS 132 using Coast Guard differential correction communicated the sprayers location to a CompaqTM IpaqTM 3850 running Farmworks Farm Site Mate VRA software. Farm Site Mate VRA transmitted recommended rates from a prescription map to the sprayer controller and logged actual application data. Field studies were conducted during 2003 and 2004 on nine different fields throughout Kansas using a reduced rate preemergence and/or postemergence VRA with prescribed rates being applied by changing sprayer volume. Errors associated with the VRA were noted. The VRA sprayer was calibrated to center the 1.5 to 2.8 m transition zone between the 7.6 by 7.6 m grid cells. Usually the transition zone consisted of a smooth increase or decrease in herbicide rate, except a rate spike was noted in situations when the prescribed rate changed from off to on. Additionally, heavy residue and/or plant canopy interfered with the radars ability to determine speed resulting in increased or decreased application rates. Even with these errors, research results demonstrated that weed patches could be managed using commercially available VRA technology.

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