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A Wireless-Controlled Variable-Rate Sprayer

Shufeng Han Assistant Professor Department of Agricultural Engineering (217) 333-2854 han@uiuc.edu

A commercial sprayer was modified for variable-rate control of 25 individual nozzles on a 60-ft sprayer boom. The variable-rate control system consisted of PWM solenoids, a pressure controller, and a nozzle control system interfaced to a computer. Map-based application software was developed that is compatible with remote sensing-based prescriptions and is capable of providing highly accurate application rate control. The system has been used successfully for in-season, site-specific nitrogen applications to corn based upon nitrogen stress maps derived from aerial images. Spread spectrum modems were implemented in the system to provide remote operation of the variable-rate application system

Figure 1. The wireless-controlled variable-rate sprayer.

System characteristics of the wireless-controlled variable-rate sprayer include:

• 6-ft high clearance sprayer capable of making nitrogen applications to corn any time during the growing season.
• 25 individually controlled nozzles capable of continuously varying the nozzle flow rate to provide highly accurate application rate control.
• Pressure compensation with the pressure controller and travel speed compensation with the nozzle controller to maintain accurate application rates.
• Map-based application control software using images as the primary data source and compatible with remote-sensing-based prescriptions.
• Wireless control of the variable-rate application system to reduce operator workload.

Currently, the variable-rate sprayer is primarily used as a research tool for conducting field-scale variable-rate experiments. The 60-ft boom width coincides with the normal treatment widths of six rows or eight rows used in our field studies. A single sprayer pass can provide a maximum treatment width of 24 rows.

The development of the variable-rate sprayer is closely related to the in-season, site-specific nitrogen management research. Instead of developing prescriptions prior to the growing season, only a fraction of the normal nitrogen rates is applied before or near planting, and additional nitrogen is applied during the growing season based on the detected nitrogen stress from remote-sensing images. The variable-rate sprayer is required to make the in-season, site-specific nitrogen applications.

Large field studies have been conducted at production fields in both Illinois and Iowa to evaluate the in-season, site-specific nitrogen management system. Field evaluation has showed promising results of the system in terms of increased yield and reduced nitrogen input. In 1998, the corn yield increased by an average of 23 bushel/acre in four study fields in both Illinois and Iowa. In 1999, the average yield increase was 7 bushel/ acre in six study fields in Iowa. In general, in-season, site-specific nitrogen application can achieve comparable or better yield as with uniform nitrogen application but often results in the reduced nitrogen input.

The current research focus is to develop a decision support system for the in-season, site-specific nitrogen applications. In addition, a ground-based, multispectral imaging sensor is being evaluated for the ability to detect corn nitrogen deficiency.

This research was previously funded by Case Corporation and is currently supported by the University of Illinois and the Illinois Council on Food and Agricultural Research (C-FAR).

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