Test of an automatic rate control system for a centrifugal-type dry fertilizer spreader

A study was undertaken to investigate the accuracy of a commercial electronic system for the control of dry fertilizer application rate on a centrifugal spreader. The components of the electronic equipment, the logical sequence of the controller functioning and the test procedure are described. The system performance was evaluated considering three fertilizers with three nominal application rates, varying the spreader forward speed in the range 6-13 km/h and measuring the corresponding flow rates. The study was conducted under stationary conditions. The results show a good linear correlation between the fertilizer flow rate and the spreader work speed. The system accuracy, expressed by the distribution of the application rate error ε, was different for the three fertilizers tested. The optimal machine response was obtained with prilled urea (100% of samples affected with a ±10% application error), while the worst one occurred when using a compound of fertilizers (only 77% of samples within the application error range ±10%).