The duration from sowing to flowering is an
important determinant of fibre yield potential in hemp, since maximum stem
yield occurs shortly after flowering. As a short-day plant, daylength has a
key influence on the timing of flowering in hemp. This paper reports on
studies into the effect of photoperiod on the thermal time duration from
sowing to flowering for 2 hemp cultivars, and develops parameters to enable
simulation of post-emergent phenology in the hemp model described in the final
paper of this series.
The hemp model divides the post-emergent period into a vegetative phase that
ends at floral initiation, aflower development phase (FDP) between flower
initiation and appearance, and a short phase between first flower appearance
and harvest maturity (male anthesis). The vegetative phase is further divided
into a temperature-dependent basic vegetative phase (BVP) and a
daylength-dependent photoperiod induced phase (PIP). For a short-day plant,
the duration of PIP is assumed to be zero degree days at daylengths below a
base or maximum optimum photoperiod (MOP). Daylengths in excess of the MOP
lead to an increase in thermal time within PIP, the duration of which is
determined by a genotype’s photoperiod sensitivity (PS).
Two hemp genotypes, Kompolti and Futura 77, were exposed to 6 different
photoperiod regimes ranging from 8 to 16 h in a growth chamber. Thermal time
durations from emergence to flower initiation and first flower formation
(harvest) were calculated from thermograph plots.
The flowering responses for the 2 cultivars were typical for a short-day
plant, with flowering occurring rapidly in daylengths less than about 14 h and
with increasing delay at longer photoperiods. With the exception of a longer
thermal time duration from flower formation to harvest maturity in the case of
Kompolti, the 2 cultivars had similar values for the key phenology parameters.
Respectively, for Futura and Kompolti: BVP was 383˚Cd and 390˚Cd,
MOP was 14 h and 13.8 h, PS was 266˚Cd/h and 252˚Cd/h, and
FDP was 76.8˚Cd and 80.2˚Cd.
Effect of industrial hemp (Cannabis sativa L) planting density on weed suppression, crop growth, physiological responses, and fibre yield in the subtropics