Keywords: Fertilizer characteristics, Fertilizer spreading, Distribution from disc.

This paper concerns the relations between the fertilizer characteristics and the spreading patterns obtained when distributing mineral fertilizers by means of spinning disc broadcasters. Fertilizer characteristics such as bulk density, mean particle size (D50) and flowability are measured for 10 different fertilizers which are spread by three different broadcasters.

The results show that there is a response between the density and flowability to the application rate but hardly no response to the uniformity in spreading when the coefficient of variation is calculated. From these results it is evident that it is necessary to have other physical parameters in mind when forecasting distribution patterns.

A distribution pattern can be forecast on the basis of statistics from a previous spreading test, for evaluation of the spreading performance of well-known spreaders. For new spreaders and for new fertilizers with unknown characteristics new methods for modelling the spreading pattern should be developed.

During the past year research has been carried out with a view to developing the above-mentioned kind of methods. A stationary test rig is used for the measurements in order to establish data concerning the behaviour of the fertilizer on the disc. For commercial discs, tests have been carried out with the purpose of measuring the amount, direction and speed of the fertilizer leaving the disc. Several combinations of machine and fertilizer parameters have been tested.

This work has provided information which explains a lot of the spreading patterns that have been made over a long period. It can be seen that characteristics such as friction and air resistance might be of importance and therefore should be tested more frequently. The work has furthermore shown that it is possible in a simple way to predict if a distribution is good or bad.

Krister Persson, Danish Institute of Animal Science, Research Center Bygholm, Horsens, Denmark.

28 pages, 14 figures, 1 table, 8 refs.