Weed Management and Economic Analysis of a Robotic Lawnmower: A Case Study in a Japanese Pear Orchard

The use of robots is increasing in agriculture, but there is a lack of suitable robotic technology for weed management in orchards. A robotic lawnmower (RLM) was installed, and its performance was studied between 2017 and 2019 in a pear orchard (1318 m 2 ) at Ibaraki University, Ami. We found that the RLM could control the weeds in an orchard throughout a year at a minimum height (average weed height, WH: 44 ± 15 mm, ± standard deviation (SD) and dry weed biomass, DWB: 103 ± 25 g m −2 ). However, the RLM experiences vibration problems while running over small pears (33 ± 8 mm dia.) during fruit thinning periods, which can stop blade mobility. During pear harvesting, fallen fruits (80 ± 12 mm dia.) strike the blade and become stuck within the chassis of the RLM; consequently, the machine stops frequently. We estimated the working performance of a riding mower (RM), brush cutter (BC), and a walking mower (WM) in a pear orchard and compared the mowing cost (annual ownership, repair and maintenance, energy, oil, and labor) with the RLM. The study reveals that the RLM performs better than other conventional mowers in a small orchard (0.33 ha). For a medium (0.66 ha) and larger (1 ha) orchard, the RLM is not more cost-effective than RM and WM. However, the existing RLM performed weed control well and showed promise for profitability in our research field. We believe that, if field challenges like fallen fruit and tree striking problems can be properly addressed, the RLM could be successfully used in many small orchards.