The use of particle ballistic modeling and pattern testing to establish robust spread patterns for New Zealand fertilizer products

Abstract. In recent years twin disc centrifugal spreaders have become larger and some manufacturers’ claim are able to spread fertilizer products as far as sixty meters. To achieve wider spread widths the fertilizer exit speed off the disc has increased. This case study uses data-mined information from a major fertilizer supplier’s quality assurance database; (Ravensdown Fertiliser Co-op Ltd.) over a 10 year period to establish mean particle size and standard deviations of a range of products used by arable and grassland farmers and studies the effect of changes in product characteristics on spread bout width. Ballistic modeling was used based on particle density, size and shape to establish the distance fertilizer particles will travel at various velocities. Fertilizer particle velocities were measured by high speed photometry using both common fertilizers and common spreaders found in New Zealand. Spreading equipment was pattern tested using the New Zealand Spreadmark method. Spreading bout widths which achieved a transverse CV of 15% are required to meet the Spreadmark standard with nitrogenous fertilizers. Spread pattern bout widths that achieved a consistent 15% CV for each product were compared to machinery manufacturers’ recommended bout widths. Ballistic modeling of particles is appropriate in ideal conditions. Often field conditions are not ideal and spreader operators achieve a more robust spread pattern as the level of spread overlap increases. The case study found that spreader operators often fail to take account of physical characteristics and target the widest bout width possible with these, new wider spreading machine. However this can lead to an in-field CV which is much greater than 15% and leads to sub-optimal utilization of the fertilizer.