Stripping of Leaves and Flower Heads to improve the Harvesting of Fibre Hemp

Hemp (Cannabis sativa) grown for fibre needs to be retted after cutting to allow the separation of fibre from the stem core. Drying of the mown stems is necessary both before and after retting but drying is likely to be hindered by the presence of leaves and flower heads on the stems. Delays in drying after retting have serious implications for fibre quality and crop spoilage when baled. The aim of this work was to determine if leaves and flower heads could be removed from standing stems by a powered rotor just prior to mowing. In a laboratory apparatus that propelled 40 stems past a rotor, the effectiveness of the method was established and the influence of rotor speed, forward speed and tooth design were examined. At every one of a range of settings, more than 92% of the contacted leaf and flower head was removed from the top 900 mm of the tested stems. A device constructed for field trials comprised a 1·2 m wide rotor on a tractor-mounted arm. Trials showed it to be effective over a range of forward speed, rotor speed and contact height. At its optimum setting of these three variables, 5·8 km h-1, 645 min-1and 1·6 m, it removed 95% of the contacted leaf and flower head material. A practical implementation would probably comprise a single machine with stripping rotor mounted ahead of the stem-cutting elements.