Taking computerized sprayers to the site-specific level, British agricultural engineers have ushered a prototype GPS-controlled "patch" sprayer system into limited production for further field testing this spring on several farms in the United Kingdom.

Based on prototype testing, the new system, compatible with all current sprayer designs may allow farmers to save up to 50% on inputs and may lead to significant environmental benefits through more judicious application of farm chemicals.

Engineers at Silsoe Research Institute (SRI) and Micron Sprayers Limited equipped the fully operational 78-ft.-boom prototype with a Massey Ferguson FieldStar mapping system, although the system is designed to work with any GPS field mapping system.

Each position along the boom has two spray nozzles instead of one. While the nozzles are conventional in design, they are computerized to match chemical output to specific requirements in the field as dictated by the computerized field map. By selecting one or both nozzles, and by varying line pressure, sprayer application rates can be varied almost continuously across the field.

The scientists first tested the prototype crop sprayer with injection metering, which, according to Paul Miller, head of SRI's chemical applications research, was "very flexible but too complicated and costly for commercial production purposes, particularly in the early stages of GPS technology."

They shifted their focus instead on trying to achieve a good "turn down" ratio from highest to lowest application rates that would still keep the chemical's physical characteristics intact.

With Micron's second-generation prototype, their goal was to retrofit the control system to work with any sprayer design. The toughest problem researchers faced during prototype development, says Miller, was in equating the dual-valve open/close sequence to the same speed as their controller, which directs an impulse almost every second.

"There was potential for under-dosing if the valves didn't open and close at the same speed," says Miller. Essentially a software problem, the glitch has since been solved. SRI, which specializes in engineering agricultural machinery, will continue to fine-tune the software and circuit cards during this spring's field tests. Once testing is complete, Micron intends to team up with sprayer manufacturers in the United States and elsewhere to market the GPS system to commercial applicators and farmers.

Miller points out that while the central control box - the crux of the system - would be available from Micron in the United Kingdom, most of the system's other components could be sourced locally.

The new sprayer is being licensed by the British Technology Group.

For more information, contact Micron Sprayers Ltd., Dept. FIN, Three Mills, Bromyard, Herefordshire HR7 4HU, UK, phone 011-44-1885-482397, e-mail micron@micron.co.uk.