Development and evaluation of a guayule seed harvester

Abstract

Guayule flowers continuously and seeds mature at different times; thus, a harvesting method that is gentle and non-destructive is required. The main objective of this study was to develop a simple but effective harvesting system capable of dislodging and collecting seed without damaging the plant. A single-row guayule seed harvester was developed after investigating different methods of seed dislodgement and collection. The harvester consisted of a seed dislodgement mechanism that removes seeds by vibration of spring steel rods. An axial flow fan placed directly over the vibrating rods catches the seed before it falls to the ground. The seed is then conveyed by the air stream through an inflatable canvas tube to a collection bin. The design and development of the seed catching system was based on terminal velocity of the unthreshed seed. Vibration frequencies ranging from 9.9 to 14.5 Hz and amplitude from 4 to 5.5 cm were used to test the harvester in the field. Harvested seed was analysed for percentages of clean seed in the harvested material, seed loss and immature seeds harvested. The performance of the machine was evaluated based on harvesting capacity and efficiency. Guayule seed harvested by the machine ranged from 1.73 to 7.18 kg/ha and harvest efficiency varied from 77 to 91%. The percentage of immature seeds removed from the crop during mechanical harvesting was as low as 0.1%. Although there was a trend for better efficiency from higher vibration frequencies, the variation was not significant. Nearly 21% of the harvested sample was clean which was much higher than that reported by other researchers. The harvester can be converted into a multiple row machine to increase its capacity.