Detailed testing of key fertiliser properties such as density and particle size distribution are routinely carried out during spinner testing. Small changes in particle properties can affect spreader performance and in order to validate experimental accuracy a detailed understand of fertiliser properties is required.
The test uses 0.5m square trays aligned in transverse rows perpendicular to the direction of travel of the spreader which collect the fertiliser as the spreader passes. The fertiliser collected in each tray is weighed with 0.1g accuracy, with the mass from each tray entered into a computer programme. The computer programme outputs a distribution curve and co-efficient of variation (COV) chart that determines the optimum width of pass in the field.
According to the Fertcare code, when spreading Urea and other granulated fertilisers the acceptable COV threshold is 15%. For non-granulated products like Lime and Gypsum the acceptable COV is 25%. The tests are carried out in the open at wind speeds below 10km/h. The spreader travels at normal operating speed (15-25km/h) over the trays.
In order to ensure statistical accuracy, the spreader must undertake a number of passes over the trays to increase the size of the sample in each tray, an equivalent application rate of 800kg/ha is recommended by the Fertcare test regime.