Seed yield in kenaf (Hibiscus cannabinus L.) as affected by sowing time in South Italy.

Kenaf is an interesting crop for fibre production, which has recently received great attention as a multipurposes crop for energy, paper pulp, thermal insulation boards and fibre-reinforced thermoplastic composites production, etc., in Mediterranean countries. Its high sensitivity to photoperiod limits seed production to the semi-arid environments of Southern Europe. In order to investigate the effects of sowing time on seed yield of kenaf in the Mediterranean climate, a 2-year research was carried out in Sicily (South Italy) adopting cv. Tainung 2, under no water restriction (100% evapotranspiration-ETc restoration) throughout the whole growing season. Four sowings per year were carried out, from late May to late June-early July. Flowering took place in a rather restricted period (late September-early October) irrespective of sowing date, confirming a strong daylength control over floral initiation. Thermal time calculated for the interval 'plant emergence (E)-flowering (F)', on average 1900.6 oCd, decreased from the first to the last sowing date in both years, as an effect of photoperiod. The photoperiodic sensitivity (PS), calculated regressing thermal time 'E-F' against photoperiod at flowering time and equal to 497.21 oCd h, can be considered as thermal time to flowering controlled by photoperiod. A base vegetative phase (BVP) of 1563 oCd and a critical photoperiod (CP) of 13.94 h were calculated for cv. Tainung 2. The photoperiod inductive phase (PIP), which describes the effect of photoperiod on flowering time and varied between 497.2 and 182.2 oCd h, allowed to predict the date of flowering with certain reliability, with values differing, in the worst case, 2 days only from the observed date. With late May sowings, the crop produced a final dry biomass (>27 t ha-1) significantly greater than that obtained with the following sowings, which approximated 15 t ha-1 in late June-early July sowings. Seed yield was negatively affected by the shift of sowing time, decreasing from over 3.5 to less than 1.6tha-1 due to a cut in number of pods per plant. According to the results of this research, early sowings of kenaf are suggested in semi-arid areas of South Italy for both seed and biomass production, maximum seed yield corresponding to maximum biomass yield, and with this last achieved with sowings of late May. The identification of both thermal and photoperiodic requirements to achieve high levels of seed yield in kenaf may help to individuate areas of seed production other than South of Italy, where however similar climatic conditions must be ensured to the crop.