DISTRIBUTION PATTERN VARIABILITY OF GRANULAR VRT APPLICATOR

Abstract

Granular applicators equipped with variable-rate technology (VRT) have gained popularity in recent years asa result of increased interest in variable-rate application. The purpose of this investigation was to characterize distributionpatterns at varying rates for different granular applicators. Uniform-rate (UR) tests were conducted to assess the accuracyof variable-rate application from four granular applicators: two spinner-disc spreaders (A and B), and two pneumaticapplicators (C and D). Pattern results indicated a consistent triangular pattern for spinner spreader B and consistent patternsfor the pneumatic applicators (C and D). However, applicator D produced pattern variations at the center and right side.Simulated overlap analysis generated CVs <20% for applicators B and C. Applicator A performed well at the two lower rates(CVs <19%) but not at the highest rate (CV = 27%). Pattern unevenness for applicator D produced CVs between 25% and34%. The spinner-disc spreaders over-applied, while the pneumatic applicators under-applied at the margins, suggesting anadjustment to the effective swath spacing or spinner-disc speed is needed to improve application accuracy. Further, overlapplots indicated pattern variability even when acceptable CVs were attained for applicators B and C. Therefore, it isrecommended that CVs accompany simulated overlap pattern plots to ensure proper calibration of VRT equipment. Swathspacing analysis indicated that three of the four applicator spacings could be changed from the recommended value to improveapplication uniformity. Pattern comparisons showed that pattern shifts occurred for applicator A (P = 0.0092) with increasingapplication rate but not for applicators B, C, and D. These results demonstrate potential application errors with VRT andthe need for proper calibration to maintain acceptable performance. Further, this investigation demonstrates the need fora VRT equipment testing standard.