AERODYNAMIC PROPERTIES OF INDIVIDUAL FERTILIZER PARTICLES

Abstract

Predictability of granular fertilizer spreading patterns is of interest from the environmental as well as the economic point of view. To ensure a constant level of uniformity of spreading patterns in the field, the Dutch government has announced their intention to require periodic testing of spreader equipment. Testing of fertilizer spreaders is traditionally carried out in large halls where spread patterns are derived from measuring fertilizer mass in collecting bins. Hofstee (1994) has developed an alternative system which measures three-dimensional velocity 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 trajectory model uses prediction equations based on the aerodynamic behavior of perfectly spherical particles. However, since fertilizer particles are in general not spherical, a method to compensate for this has been developed. This method uses the ratio between measured and modeled fall times, and is expressed in a parameter, the diameter coefficient. Once this parameter is assessed for a specific material, it can be used 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 about the fall time of individual fertilizer particles, falling from a constant height. The materials used in this research were Calcium Ammonium Nitrate (CAN 27 N), Nitrate Phosphorous Potassium (NPK 12-10-18) and Potassium 60. They were chosen for their wide-spread use and different shape characteristics. The diameter range of particles used in the research was 1 to 4.75 mm.