2014 FLRC Workshop – Miles Grafton

The ballistics of separation of fertiliser blends at wide bout widths

Presenter: Miles Grafton

In recent years some New Zealand arable farmers have experienced crop striping when spreading blended fertilisers. These farmers have not experienced the phenomenon prior to upgrading spreading equipment, capable of spreading to tram lines spaced at 30m plus. Fertiliser companies have been criticised as the blends used are no different to those used previously and in some cases have been recommended by the fertiliser companies’ representatives.

Tram line spreading is generally very accurate. Spreaders are pattern type tested by manufacturers based on particle size, uniformity of particle size and bulk density, to achieve a pattern overlap which delivers the minimum spread variation possible, given the fertiliser particle parameters.

Spreading to a 30m tramline requires fertiliser particles to spread to at least 22.5m from each disc to allow for the require spread overlap, as spread overlaps of around 50% are common. To propel particles 22.5m from a height of 1.5m requires them to be despatched at around 60ms-1. At these speeds blended fertilisers split as their rate of deceleration through drag force is based on particle density, size and shape in order of importance. This paper quantifies the impact of drag force on typical fertilisers and demonstrates the relationship between increasing bout widths and greater separation of blends.

In addition a twin disk arable spreader was spread-pattern tested using the New Zealand Spreadmark test with typical high analysis fertilisers. Fertiliser particles discharging from the disks were filmed using high speed photometry and ballistic modelling compared to the pattern test.

Keywords: Drag force, Ballistics, Blended fertilisers, Blend separation, in-field coefficient of variation, high speed photometry

Presentations from the Fertilizer and Lime Research Centre (Massey University) Workshop. The indicative information about this workshop is the ‘Proceedings’ accessed through the ‘Publications’ page on the website (http://flrc.massey.ac.nz/). These are the manuscripts provided by the authors, and it is these that must be cited when referring to the information presented at the workshop.