Development of a hemp (Cannabis sativa L.) simulation model 1. General introduction and the effect of temperature on the pre-emergent development of hemp
Sn. Lisson et al., Development of a hemp (Cannabis sativa L.) simulation model 1. General introduction and the effect of temperature on the pre-emergent development of hemp, AUST J EX A, 40(3), 2000, pp. 405-411
In recent times, there has been a revival of interest in hemp (Cannabis sat
iva L.), principally as a source of fibre in paper and pulp manufacture. St
udies assessing the production potential and optimum crop management of hem
p could benefit from the use of a simulation model that captures crop growt
h and development processes in response to management, genotypic, soil and
climate factors. Such a model would complement the more traditional agronom
ic field trial programs by helping to identify the need, extent and nature
of such trials, and by extrapolating limited field results across both temp
oral and spatial dimensions.
The hemp model described in the final paper in this series, divides crop ph
enology into 5 phases, the first of which includes the pre-emergent process
es of germination and the subsequent elongation of hypocotyl and radicle. T
his first paper reports on a study into the response of these pre-emergent
processes to temperature. The primary objectives were to establish a simple
model for predicting the duration from sowing to emergence and to obtain e
stimates for the cardinal temperatures of hemp growth and development. Card
inal temperatures are required for the estimation of thermal time, which dr
ives phenological development and canopy expansion in the hemp model.
The germination response of the hemp cultivar Kompolti was measured at 13 d
ifferent temperatures in incubators set between 1 and 55 degrees C. Similar
ly, the response of radicle and hypocotyl elongation to temperature was mea
sured at 8 different temperatures in incubators set between 10 and 40 degre
es C. Development rates for each phase of pre-emergent development were the
n calculated from time response plots of germinant number, hypocotyl and ra
dicle length. Finally, piecewise linear models were fitted to plots of deve
lopment rate versus temperature in order to calculate thermal time duration
s for each phase and cardinal temperatures for hemp growth and development.
Estimates of the optimum and maximum temperatures from the elongation stud
y were relatively consistent, with average values of 28.6 and 40.7 degrees
C, respectively. Base temperature estimates were less consistent, ranging f
rom 1.4 degrees C for the hypocotyl linear phase, to 6.2 degrees C for the
radicle lag phase. This variability made it difficult to identify a common
base temperature for use in the hemp model. However, there was some evidenc
e to support previously reported base temperature estimates ranging from 0
to 2.5 degrees C. Assuming a common base temperature of 1 degrees C, the av
erage thermal time requirements for germination and the lag and linear phas
es of hypocotyl elongation were 24.1 degrees Cd, 44.5 degrees Cd and 1.34 d
egrees Cd/mm, respectively.