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A Model to Analyze “As-Applied” Reports of Variable Rate Applications

A. F. Colaço, H. J. Rosa, J. P. Molin

University of São Paulo

Variable rate technology enables users to access crop inputs such as fertilizers and pesticides, based on site specific information. This technology combines a variable rate control system, positioning system and GIS software to enable variable rate application. During operation some of these systems report information (“as-applied” files) about target rates and actual applied rates on georeferenced points along the tracks. These reports, even if a simple feedback from the controller signal, are useful for operation quality control and documentation but they haven`t been widely used at their potential. Thus the goal of this study was to create a simple, flexible, user friendly tool capable to analyze “as-applied” files quantifying and locating off-rate errors and their possible sources. A model was developed on an electronic spreadsheet; it calculates off-rate errors and classifies them as less than target rate, acceptable or over the target rate. Error possible causes are classified on three types: vehicle path position (inward, middle or outward), high rate change (step up or down) and vehicle acceleration or deceleration. Classification of errors and their causes is based up on settable limits. The model provides 54 combinations of errors and possible sources that can be ranked and viewed on the application map. As examples, data from two scenarios were analyzed, from a self-propelled pneumatic machine and an orange pulled applicator, booth applying granular fertilizers. On average 30.6 % of recorded points were considered application errors (10 % off the target rate). 70.5 % of them occurred on high rate change points on the first scenario and 69.7 % on acceleration/deceleration points on second scenario. The results are consistent to the application conditions on each field. The model was efficient to determine the main and minor application error causes, showing their distribution through maps which allow users to access operation quality control and guide equipment improvement efforts.

Keyword: variable rate; as applied files; application errors; quality control; model

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