RATE RESPONSE ASSESSMENT FROM VARIOUS GRANULAR VRT APPLICATORS

Abstract

Variable-rate technology (VRT) adds complexity to application equipment, thereby confounding the assessmentof applicator performance. The intent of this investigation was to assess the rate response of various VRT granularapplicators: two spinner spreaders (A and B), and two pneumatic applicators (C and D). Variable-rate (VR) tests wereconducted to quantify the rate response characteristics (delay and transition times) for the applicators. A sigmoidal functionwas used to model the rate response for five of the six tests. Applicator A exhibited a linear response during decreasing ratechanges. Results indicated that only applicator B demonstrated consistent delay and transition times, enabling the use of asingle look-ahead time for rate response time correction. Contouring of prescription maps increased the transition timesfor applicator D by enlarging the adjustment area between management zones. Rate changes were quicker for the two newerVR control systems, signifying advancement in hydraulic control valve technology. This research illustrates the need forstandard testing protocols for VRT systems to help guide VRT software developers, equipment manufacturers, and end users.