Field trials comparing robotic and manual mowing were continued at NIBIO Landvik, Norway, with robotic (Husqvarna 550) and cylinder mowers on fairway (mowing height 15 mm). On semi-rough (mowing height 35 mm), the same robotic mowers were compared with rotary mowers. Similarly high turfgrass quality on fairway and semi-rough was found with robotic and manual mowing. On some observation dates, less disease was found with robotic mowing, which could be explained by more frequent dew removal by the robots. Less white clover was found on robotic-mown fairway, while more white clover was found in robotic-mown semi-rough.
The N fertiliser effect of return of clippings in robotic vs. manual mowing was studied on fairway with annual N rates of 0, 3, 6, 9, and 12 g/m2/yr applied over the season. There was no evidence that daily robotic mowing, compared with manual mowing three times a week with clippings returned, reduced fertiliser requirements on fairways due to better utilisation of nitrogen (N) in the smaller clippings volume. Overall, there were only small and insignificant differences in turfgrass visual quality and N utilisation between robotic and manual mowing that both returned clippings, but manual mowing with removal of clippings reduced turfgrass quality. However the results indicated a trend for more benefit from robotic mowing compared with manual mowing at high fertility resulting in high turfgrass growth rates. Under dry condtions and with insufficient fertilisation, weeds, especially white clover, increased more on robotic-mown fairways than on manually mown fairways.
The contradictory results obtained on encroachment of white clover on fairway in robotic and manual mowing call for further research. For robotic mowing to be recommended as a more sustainable mowing system than conventional mowing, it is important to know whether white clover increases or decreases with robotic mowing, which depends on factors such as grass mixture, fertiliser rate, water availability/irrigation and mowing height. Large-scale demonstration trials with robotic mowers in comparison with cylinder mowers on fairways and rotary mowers on semi-roughs were laid out at five golf courses in Scandinavia. Turfgrass quality, coverage of broadleaved weeds and energy use were recorded monthly by the course managers. In these trials, turfgrass quality was mostly similar for robotic and manual mowing on fairways and semi-roughs, but the robots were superior at high growth rates. Course managers reported less soil compaction with robots, resulting in improved water drainage on areas with robotic mowing for 2-3 years. Robotic mowing also resulted in less soil compaction in the experimental semi-rough at Landvik.
A surveys of golfers indicated that they were positive or neutral to robot mowing, but they wanted local rules when robots interfere with the game. Unfortunately, due to malfunction of loggers, the ROBO-GOLF project was unable to assess changes in energy use and CO2 footprint on switching from traditional (manual) to robotic mowing. Further research is needed to answer these questions.
