Agriculture Reference
In-Depth Information
•
Chambre d'Agriculture de l'Eure: field tri-
maturing varieties. The growth curves are
again parallel after the end of flowering.
The daily growth rate is dependent on the
stage of growth and follows a parabolic curve.
Growth is slow during the establishment phase
and then increases regularly (although slower and
slower) up to an average of 6 cm/day, before
then falling off (FNPC, 2000); see Fig. 5.3. The
early and late developing varieties both behave in
the same manner. The earliness of a variety is
judged by the date on which the daily growth rate
is maximum. The curve for the late maturing vari-
ety shows an inflection later, this point appearing
to correspond with the start of flowering for this
variety.
The fastest relative speeds (per cent of
daily growth relative to the size of the plant) are
attained during the establishment phase (1.0-
15% growth/day). This is maintained during
the active growth phase before falling off rap-
idly to zero at the end of flowering.
als undertaken in the 1990s.
FNPC: replicated trials undertaken between
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1970 and 2002.
ITC: replicated trials undertaken by the
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FNPC in 2003 and field trials undertaken
by the SPC Seine-Saône in 2003.
1
Experimental protocols differ from one year to
the next and between organizations. This is
true for most subjects studied and makes the
comparison of results problematic and the cal-
culation of averages across large numbers of
experiments difficult.
For this reason, we have chosen to con-
struct certain graphs using relative averages:
Relative average yield = [(yield × 100)/
maximum yield]/
n
Relative average fibre content = [(fibre
content
×
100)/maximum
fibre
content]/
n
where
n
is the number of trials.
5.2.2
Establishing yield parameters
Dry weight of hurds
5.2
Physiology of Hemp
During the active growth phase, the yield of
fibre, hurds and seeds develops as a linear
function of growing degree days (GDD)
(Fig. 5.4). This stabilizes from the start of
flowering and, in the 4-5 days following this
date, the final hurd yield is definitively
established.
NB: The temperature requirements to
produce hurd dry matter vary depending on
the amount of nitrogen applied. The more
nitrogen, the lower the GDD requirement (less
than 120 GDD for nitrogen doses of >150
units/ha). The lower the amount of nitrogen
supplied, the greater the GDD requirements:
up to 300 GDD where no nitrogen fertilizer is
supplied and there is an absence of nitrogen in
the soil (FNPC, 2000, 2002).
5.2.1 Growth
Several systems are in existence today allowing
the stage of growth of the hemp plant to be deter-
mined. The two most popular systems are those
of Médiavilla (Table 5.1) and the FNPC (Fig. 5.1).
At present, the former is suited best to producers,
for it allows a computer record of the observations
made during the growth of the plant.
We divide the growth of hemp into four
phases (Fig. 5.2; FNPC, 1999, 2000):
1. Establishment (3 weeks).
2. Active growth.
3. Slowing in growth at the start of flowering.
4. Growth arrest at the start of full flowering.
The only characteristic that distinguishes varieties
is the
earliness
of the crop, i.e. the time between
emergence and flowering for female plants.
Whether we study early or late maturing
varieties, the growth curves before flowering
are strictly identical. A difference is seen only
at the start of flowering: the early varieties
flower and stop growing earlier than the late
Fibre levels
This corresponds to hurd yield.
Seed dry weight
The seed dry weight increases regularly from
the point of full flowering to the point of grain
