Verification of Granular Spreader Distribution Patterns At Multiple Rates.

Varying application rates of 2 or more separately metered ingredients may be prescribed for precision agriculture, yet standard commercial spreader calibration is usually performed with one ingredient applied at one rate.  This project measured patterns from applications ranging from 28 to 224 kg ha^-1 of one or two ingredients applied by multi-bin spreaders, two spinners and one air-boom.  Results were similar for relatively inexpensive plastic collecting pans and metal pans custom built to ASABE specifications, suggesting the validity of calibrations using plastic pans for routine field work not subject to any legal certification or scientific rigor criteria.  Measured fertilizer rate 95% confidence intervals usually differed from the target rates.  While all spreaders had a 20-30% error within the 56-224 kg ha^-1 range, only two of the three spreaders maintained even this reasonable accuracy level at the 28 kg ha^-1 range.  Considerable variation was found among rates of the two ingredients when intended to be applied at the same rate by dual bulk bin spreaders.  A smaller micronutrient bin, however, appeared to deliver product with relative consistency regardless of the simultaneous application rate of a bulk bin product.  Although no fertilizer application methodology will achieve perfect accuracy or uniformity, results such as these should assist spreader operators in optimizing equipment settings to more nearly achieve target application rates.