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Evaluation of Deposition and Application Accuracy of A Pulse Width Modulation Variable Rate Field Sprayer

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

Citation:  Paper number  011077,  2001 ASAE Annual Meeting. (doi: 10.13031/2013.3432) @2001
Authors:   Robert A. Pierce, Paul D. Ayers
Keywords:   Pulse width modulation, sprayer, variable rate technology, longitudinal uniformity, water sensitive paper, droplet size efficacy, pre-emergence herbicide applications, postemergence herbicide applicat

Due to over applications of agricultural chemicals, concerns of chemical costs and environmental contamination continue to increase. From these concerns, there has been a great deal of devotion to the development of accurate variable rate technologies to increase spraying efficiency. The type of variable rate technology that is discussed in this paper is pulse width modulation. This is a technology that controls the length of a nozzle valve pulse duration (i.e., pulse width) used on field sprayers. This paper discusses the performance of this technology and its effectiveness on weed control from herbicide applications. Performance analysis of the sprayer technology indicated that nozzle flow rate variation along the boom was acceptable with a coefficient of variation less than 2%. Changes in nozzle flow rate were approximately proportional to the duty cycle setting with an average error of 4% from the theoretical. In addition, the spray pattern uniformity along the length of the boom was tested at various duty cycle settings. A desirable spray pattern was found with a coefficient of variation less than 10%. This suggests that intermittent spray clouds had no effect on spray pattern along the boom. Although nozzle pulsing had no effect on the spray pattern along the boom, uniformity of spray pattern in the direction of travel was studied. It was found that the coefficient of variation varied from 65% to less than 10% at duty cycle settings ranging from 25% to 100%. Due to this large variation in spray pattern along the direction of travel, an efficacy evaluation of post and pre-emergence herbicide application were performed using pigweed as the indicator species. The weed control varied from 65% to 100% at duty cycle settings of 25% to 100% for the postemergence herbicide application. Weed control for pre-emergence herbicide application was found to be nearly 100% for all duty cycle settings. This shows that the longitudinal uniformity at certain low pulse widths have an effect on resulting weed control from postemergence herbicide applications; however, it has little to no effect on weed control from pre-emergence herbicide applications.

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