Preliminary results of tests facing with the controlled retting of hemp

An important component of the implementation of the hemp crop management is the microbiological retting of the straw. At the Experimental Institute for Industrial Crops, research has been focused on this topic and in 1997 trials of retting performed in tanks placed in the laboratory or in open field were carried out. Cultivar 'Fibranova' was employed, harvested at the time of full flowering. For the laboratory tests, 12 plastic tanks containing well water were used. One of these was taken as the control and each of the remaining 11 tanks were inoculated with different strains of Clostridium felsineum. Four different retting times were experienced (3, 6, 9 and 12 days). The fibre was assessed for the morphological, chemical and physico-mechanical properties. The retting in open field was performed in four concrete tanks; (1) in pond water in an open tank, (2) in pond water in a tank covered with a transparent plastic film (to raise the temperature of the water), (3) in well water in an open tank and with the addition of a culture of C. felsineum, and (4) in well water in an open tank, without the addition of C. felsineum. Six increasing retting durations were adopted (2, 4, 6, 8, 10 and 12 days). The fibre obtained was evaluated taking into account colour, softness and fineness. The results obtained indicated that the water type, the temperature of retting water and the bacterial inoculum all influenced the duration of the process and the quality of the fibre. Retting was completed in 6 days in pond water and in 12 days in well water. Raising the temperature of water from 24 to 28 degrees C reduced the duration of the process from 6 to 4 days. It was found that the bacterial strains 'L1-6' and 'C1-6' of C. felsineum reduced the duration of the retting process from 12 to 6 days (with a water temperature of 20 degrees C), leading to a clearer, softer and finer fibre. (C) 2000 Elsevier Science B.V. All rights reserved.