Agriculture Reference
In-Depth Information
in situ
at worst. The optimal time is very much
dependent on the weather conditions during
any given year (excepting a period of drought,
which can stop vegetation during full flower-
ing, as was the case in 2003). The determi-
nant factor is the variety's precocity (earliness),
defined as the date of its full flowering.
Approximately 40 days can then be added to
this in order to determine the optimal time to
harvest the seed.
Thus, for early French varieties and under
the conditions typical of north-eastern France,
harvesting starts around 12 September, with
a peak around 19/20 of that month. At this
time, four-fifths of the seeds are mature. In
order to ripen the fraction of seeds that are
still green, a further 10 days would be required,
together with the accompanying risks out-
lined above. USO31, which is the earliest by
10 days, arrives at an optimal point around
10 September (Fig. 6.3).
The setting up and adjustment of the
combine harvester can also impact on the
quality of the hemp seed. It is necessary to
turn the arms at a slow speed (approximately
300 turns/min) in order not to hit the grains
too hard. The counter beater must not be too
tight (although it must not be too loose either,
as there must be room for manoeuvre where
blockages occur) and cleaning must be suffi-
ciently energetic to eliminate the maximum
amount of impurities (empty seeds, green
seeds, leaf fragments and hemp hurds). When
the hopper is emptied, the emptying screw
must not turn too fast in order to avoid any
further unnecessary damage.
As a general rule, the moisture of the
hemp seed is above 20%. Producers from the
LCDA are required to deliver a product with a
moisture level of less than 27.5% and/or an
impurity content below 25%. The quality of
the hemp seed can deteriorate very rapidly and
100%
90%
80%
70%
60%
50%
40%
30%
20%
Fig. 6.2.
Control of the combine harvester. The germination rate is correlated with the speed of the beater.
20
FINOLA
USO
F34
15
10
5
0
-5
Fig. 6.3.
Evolution of the yield as a function of the harvesting date and earliness (modified from
Densanlis, 2001).
