Comparison of VRT granular applicators

Granular applicators equipped with variable-rate technology have gained popularity in recent years due to increased interests in variable-rate application. The purpose of this investigation was to characterize distribution patterns at varying rates and quantify rate transitions from various granular applicators. Both uniform- and variable-rate tests were conducted to assess the accuracy of variable-rate application from four granular applicators (2 spinner spreaders and 2 pneumatic applicators). The patterns results indicated a consistent triangular pattern for spinner spreader B and consistent patterns for pneumatic applicators C and D. However, applicator D produced pattern variations at the center and right side. Simulated overlap analysis showed that applicators B and C performed acceptably (CV's< 20%). Applicator A performed well at the two lower rates but not at the highest rate (CV=27.4). The pattern unevenness for applicator D produced undesirable CV's between 25% and 34%. Pattern comparisons showed that pattern shifts occurred for applicator A (P=0.0092) but not for applicators B, C, and D. Rate transition tests produced inconsistencies in the delay and transition times for applicators A, B, and D. For these three applicators, their transition times were much longer for the low to high rate change. Applicator C illustrated consistency with delay times around 1.2 to 1.5 seconds and quick transition times (<0.4 sec.). These results demonstrate potential application errors with variable-rate technology which should assist software and equipment manufacturers to develop more accurate products and ultimately the need for a testing standard for this type equipment.