AERODYNAMIC PROPERTIES OF INDIVIDUAL FERTILIZER PARTICLES

Predictability of granular fertilizer spreading patterns is of interes t from the environmental as well as the economic point of view. To ens ure a constant level of uniformity of spreading patterns in the field, the Dutch government has announced their intention to require periodi c testing of spreader equipment. Testing of fertilizer spreaders is tr aditionally carried out in large halls where spread patterns are deriv ed from measuring fertilizer mass in collecting bins. Hofstee (1994) h as developed an alternative system which measures three-dimensional ve locity vectors within a cylindrical sampling zone behind the spreader It also simultaneously estimates individual particle diameters. These measured quantities serve as initial conditions in a trajectory model that predicts landing spots for individual particles. After a test run the complete set of landing spots represents a spread pattern. The tr ajectory model uses prediction equations based on the aerodynamic beha vior of perfectly spherical particles. However since fertilizer partic les are in general not spherical, a method to compensate for this has been developed. This method uses the ratio between measured and modele d fall times, and is expressed in a parameter the diameter coefficient Once this parameter is assessed for a specific material, it can be us ed as a correction factor in the trajectory model. In this research a fall test is used as a robust and simple method for collecting data ab out the fall time of individual fertilizer particles, falling from a c onstant height. The materials used in this research were Calcium Ammon ium Nitrate (CAN 27 N), Nitrate Phosphorous Potassium (NPK 12-10-18) a nd Potassium 60. They were chosen for their wide-spread use and differ ent shape characteristics. The diameter range of particles used in the research was 1 to 4.75 mm.