Effect of lighting conditions and ground speed on performance of intelligent fertilizer spreader for spot-application in wild blueberry

Wild blueberry fields have a significant proportion of bare spots/weed patches, scattered throughout the field, emphasizing the need for targeted fertilizer applications. The existing prescription map-based variable rate (VR) spreader cannot take account of the presence of small, irregularly shaped bare spots/weed patches during fertilization as only each half of the boom (3.66 m; 6 nozzles) is controlled—not each individual nozzle. The objective of this study was to modify the existing VR spreader for spot-application (SA) of fertilizer only in plant areas. The sensing and control system developed was capable of discriminating bare spots/weeds from plants, and shifting the independent control from 6 nozzles (3.66 m) to each pair of nozzles (1.22 m). The modified VR granular (MVRG) fertilizer spreader was able to use a prescription map and the sensing and control systems simultaneously within a field, to avoid fertilization in variable sized bare spots/weed patches. The performance of the MVRG fertilizer spreader was evaluated under two different lighting conditions and three ground speeds. Twelve bare spots/weed patches and plant areas were randomly selected in the wild blueberry field and weighed sticky collectors were placed to collect clay filler which was used as an analogue of fertilizer. The MVRG fertilizer spreader was operated on SA (application only in plant areas) and uniform (application in plants and bare spots/weed patches) modes alternately and the collectors were collected and re-weighed. Results of this study suggested that the MVRG spreader was capable of detecting plants/bare spots/weeds for SA of fertilizer. Spot application of fertilizer can help to reduce excessive fertilizer usage in bare spots/weeds, which will increase farm profitability.