Case Study: Distribution Uniformity of a Blended Fertilizer Applied Using a Variable-Rate Spinner-Disc Spreader

Blended fertilizers are commonly applied to crop and pasture land using spinner-disc spreaders. However, the nature of blended fertilizers can make it difficult to spread uniformly due to varying physical properties of the N, P, and K raw constituents, which can lead to segregation during application. Further, variable-rate application of blended fertilizer could pose challenges in terms of accuracy and uniformity to meet target prescription rates. Therefore, the objective of this study was to evaluate the potential of fertilizer segregation during application with a spinner-disc spreader. A series of standard pan and field tests were performed to evaluate mass and nutrient distribution for a blended fertilizer (17-17-17) using a spinner-disc spreader. Field tests were performed by generating prescription maps, randomly placing pans across the field, then applying the blended fertilizer and analyzing the collected material for N, P₂O₅ and K₂O mass fractions. Both mass and nutrient distribution patterns were generated and then compared. Field data in combination with prescription and as-applied maps were used to evaluate spreader performance and product segregation. A rating of 17-18-17 was determined for the blended fertilizer. P₂O₅ and K₂O mass fraction varied significantly (coefficient of variation, CV, 25.0% and 26.0%, respectively) based on the single-pass pattern measurements. Field application also produced high variability of P₂O₅ and K₂O mass fractions with CV’s ranging between 16.8% and 37.2%, respectively. These results indicated the occurrence of fertilizer segregation. Nitrogen mass fraction, spread variability was low (CV = 4%) based on the pan tests but was contributed to N being provided by both ammonium nitrate and diammonium phosphate (DAP) constituents of the blend. Particle size analysis supported the notion that segregation occurred mainly due to size variability between the constituents. During field tests, actual rates were consistently higher than the prescribed rates. While the prescription and as-applied maps showed high correlation (R = 0.75 to 0.94), the as-applied maps did not reflect the actual field application (R = 0.25 to 0.67). Finally, the existence of fertilizer segregation indicated further research is required to understand segregation of blended fertilizers when applied using spinner spreaders.