Abstract
A spatially variable rate herbicide application system was developed and a site-specific evaluation of its fieldperformance and accuracy was conducted. A 4.2-ha (10.4-ac) field was sampled on an 18.3-m (60-ft) grid for soil typeand organic matter percent (OM%). A herbicide management table was used to determine the appropriate activeingredient (AI) application rate for each area of the field depending on spatial variation of field parameter data (soil typeand OM%). Application rate of AI varied from 3510 mL/ha (1.5 qt/ac) up to 5260 mL/ha (2.25 qt/ac). Using geographicalinformation system (GIS) software, a georeferenced map (management map) of field application rates was produced. Adirect nozzle injection field sprayer was equipped with a real-time differentially corrected global positioning system(DGPS). A program was developed to receive on-the-go the sprayer position data (latitude and longitude) and retrieve thedesired application rate from the GIS map at the current sprayer field position. A datalogger was used to changeon-the-go the AI flow rate (water was used as a substitute for the AI) to correspond with the desired application rate at aspecific sprayer ground speed and field position. To evaluate the system accuracy in reproducing the management map,data was collected from the DGPS to determine its field accuracy. DGPS data and datalogger output (data produced bysprayer monitoring sensors) along with the GIS map were utilized to reveal the spatial accuracy of the application system.Control system reaction time and accuracy were investigated using data from the datalogger program output. Resultsrevealed that the DGPS maintained an accuracy of at least 1 m (3.3 ft). Spatial analysis showed that the applicationsystem reproduced the application rate management map. On the average, the greatest reaction time of the control systemwas 2.2 s. For the four application rates used in the study, the highest average application rate error was 2.0%.
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