Int.J.Curr.Microbiol.App.Sci (2020) 9(11): 3638-3645 3638 Original Research Article https://doi.org/10.20546/ijcmas.2020.911.436 Laboratory Investigation of Detopping Unit for Mini-tractor Operated Harvester for Small Onion (Allium Cepa var. Aggregatum) R. Sai Prasanth 1* , P. K. Padmanathan 1 , S. S. Sivakumar 1 and V. Alex Albert 2 1 Department of Farm Machinery and Power Engineering, 2 Department of Basic Engineering and Applied Sciences, AEC & RI, Kumulur, India *Corresponding author ABSTRACT Introduction Onion (Allium Cepa var.) is the second most important vegetable crop in the world. It is a native crop of Asia and was introduced in India by Palestine. As it is one of the basic indispensable vegetables, the demand for onion bulbs has remained fairly consistent irrespective of wide fluctuations in the market prices. India is the leading exporter of fresh onions, 1.902MT of onions were exported in 2018-19. According to Ministry of Agriculture, for the year 2017-18 the area of onion cultivation is 1.284 M ha with 23.26 MT productions. The area of onion cultivation in the state of Tamilnadu is 28,360 ha with production of 0.301 MT in 2017-18. The other major states that are producing onions in the country are Maharashtra, Gujarat, Karnataka, Uttar Pradesh, Andhra Pradesh, Orissa, Madhya Pradesh, Rajasthan and Bihar. International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 11 (2020) Journal homepage: http://www.ijcmas.com In India, detopping of onion is carried out mostly by manual operation after uprooting of the onions which is tedious and time consuming. In this study, laboratory evaluation of mechanized detopping unit was demonstrated before uprooting the onions. The crop was grown in plastic trays with spacing of 20 x 12cm. The detopping unit consists of vertical shaft attached with cutting thread at the bottom end. Reinforced composite nylon material was chosen as cutting material due to its extra strength and high resistance to breakage. The nylon thread detops the onion leaves in rotary cutting as line trimmers. Based on the cross sectional area, three different types of threads (square -T 1 , round - T 2 and flat with one side serrated - T 3 ) were selected for evaluation of detopping unit. The detopping unit was evaluated at three levels of peripheral speed (5.31- N 1 , 6.64 - N 2 and 7.97 m s -1 - N 3 ) of the unit, and three forward speeds (1 - S 1 , 1.5 - S 2 and 3.4 kmph - S 3 ) using sticky belt. The better performance of detopping onion was observed in square shaped cross-sectional type (T 1 ) nylon string with both four strings and eight strings (H 2 andH 3 ) for the average onion neck length of 23 mm and it was sufficient for minimising storage losses of onions. The optimum peripheral speed of detopping unit was observed as 6.64 m s -1 with forward speed of 1 kmph. Keywords Detopping, Onion harvester, Onion neck length, RSM methodology Accepted: 24 October 2020 Available Online: 10 November 2020 Article Info