Distribution uniformity of blended versus independently metered granular fertilizers using a variable rate spinner disc spreader

Background: Broadcast fertilizer distribution using spinner-disc spreaders equipped with variable-rate technology has become a widely adopted practice. However, a few spinner-disc spreaders provide dual bins permitting the independent metering of two products. The questions at hand does the individual fertilizer distribution pattern vary if two products are applied in blended form or independently metered onto the spinner discs. Therefore, this study compares the distribution uniformity of a common phosphorus and potassium fertilizers applied using variable-rate technology in blended versus independently metered forms. Methods: A common US spinner-disc spreader with a dual bin, and the ability to independently meter two products onto the spinner-discs was used for this study. Prior to spreading fertilizer, particle analysis determined that the bulk density of diammonium phosphate (DAP), muriate of potash, and a blended fertilizer (10-26-26) were 1009, 1105, and 1025 kg m-3, respectively. All three fertilizer mixtures were broadcast and nutrient distributions determined using standard procedures. Different spinner disc speeds (600, 700 and 800 RPM) and application rates (220 and 440 kg ha-1) were included as treatments. Results and discussions: Results indicated differences between independently metered DAP and potash versus blended. Distribution patterns did not vary at the different application rates. Also, it was found that the application rate and divider position had no effect on the efficiency of fertilizer distribution, while the disc speed improved distribution uniformity. Conclusion: These results indicate that while spinner-disc spreaders are inefficient by nature, opportunities exist to increase distribution uniformity through using newer technology such as dual bin spreaders