Considering field topography in the model-based assessment of a centrifugal spreader's variable rate application accuracy

In the application of solid mineral fertilizers with twin-disc spreaders, accurate delivery of the prescribed rates is highly dependent on their dynamic performance. Additional to the effect of imprecision in geolocations and the delayed reaction of the spreader to the rate updates at the delineations of the task map, the field surface with inclined hills and undulating waves significantly influences the field application accuracy. In this paper, the effect of the determined field topography on application accuracy has been assessed. Necessary sensors such as the prism of a Total Station and an IMU (Inertial Measurement Unit) have been attached to a mobile sled to acquire the geo-referenced positions together with its real-time tilting information while following the actual field profile. A model for the spreader performance on a flat field surface, which had been developed by the authors in previous work, was improved by incorporating the measured tilt information corresponding to the measured field conditions. In addition, the improved model used the measured topography with inclinations and undulations to determine the landing location of each fertilizer particle. The influence of the determined field inclinations and undulations on the stationary spreading was assessed by comparing the distributions of the fertilizers in the transversal direction that are extracted from the spreading on the flat and measured field surfaces. The comparative analysis of the distributions indicated a significantly high value of 27.8% for a root-mean -squared deviation. The subsequent assessment of the actual field topography's effect on the spreader's dynamic performance showed that the measured field surface conditions have a significant effect on the application accuracy in terms of absolute deviation, with approx. 5% under-and approx. 3% over-application of the maximum prescribed amount.