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Technical Note: Evaluation of a Rhodamine-WT Dye/Glycerin Mixture as a Tracer for Testing Direct Injection Systems for Agricultural Sprayers

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

Citation:  Applied Engineering in Agriculture. 28(3): 643-646. (doi: 10.13031/2013.42424) @2012
Authors:   J. D. Luck, S. A. Shearer, B. D. Luck, F. A. Payne
Keywords:   Pesticide application, Precision agriculture, Spraying equipment, Pesticides

The purpose of this study was to provide valuable insight regarding the use of Rhodamine WT (red) dye as a tracer for evaluating injected concentrations. More specifically, the effects of mixing the dye with glycerin to simulate the viscosity of a pesticide (e.g., glyphosate) or injecting the dye/glycerin mixture into deionized (DI) versus tap water on developing appropriate calibration equations were evaluated. Test results indicated that mixing the dye in a solution of glycerin and DI water significantly affected absorbance measurements compared to the dye mixed solely in DI water. The error in estimating absorbance was 7.4% between the two calibration equations. Therefore, any calibration curves must include a solution containing glycerin to compensate for this. Absorbance results also indicated that potable tap water could be used to simulate the spray carrier as opposed to the DI water. A calibration curve was developed for the simulated pesticide (dye/glycerin/DI water solution) injected into the carrier (tap water) for solutions ranging from 2,000:1 (carrier:pesticide) to 500,000:1; an overall dilution range of 250:1. This dilution range exceeded typical pesticide tank-mixed dilutions which were on the order of 11:1 for the application of glyphosate for corn or soybeans. The regression model standard error for predicting the dye concentration based on absorbance measurements was 5.3x10-6.

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