Agriculture Reference
In-Depth Information
Where the southern hemisphere is con-
cerned, trials conducted in Bathurst, South
Africa, in 2003, produced similar conclusions,
but with at an interval of 6 months.
their germination and the vigour of the
young plants.
ROLLING
.
Rolling can be necessary in order to
smooth the soil after sowing and to promote
germination under dry conditions. It is recom-
mended, however, that prudence be exercised,
in particular on silty soil subject to rain batter-
ing or rolled and then heavily rained on, as
these will penalize emergence. Rolling can also
be of value where the soil has a calcareous-clay
character, as this procedure will push stones
into the soil. This makes cutting the crop easier
at harvest and reduces the number of stones
picked up with the hurds and incorporated into
the bales. In these cases, rolling can be under-
taken later, when the hemp has already
emerged, up until the 10 cm stage.
Depth of sowing.
The planting depth for hemp
is similar to that practised for other crops: the
depth should be eight times the length of the
seed. When conditions are particularly dry, a
depth of 2-3 cm places the seed in soil that
is still humid. At a later time, when conditions
are more humid, shallower sowing is recom-
mended. The germination rate declines rapidly
as soon as the sowing depth increases beyond
3 cm, particularly in silty soil that has been
compacted by rain.
Sowing type.
The means of spreading hemp
seed, either in line or randomly, does not
affect the behaviour of the crop. The degree
to which the hemp crop smothers weeds does
not appear to differ between either seeding
method. It is therefore not necessary, as it is
for flax, to use special equipment on the seed-
ing machinery.
Fight against weeds, diseases
and other pests
WEEDS
.
Hemp's ability to smother out weeds is
weak during the early stages of growth but rap-
idly becomes significant until the point where it
can suffocate all weeds. Until that point is
reached, when the crop covers the whole
ground, there is a real risk that weeds can gain
the upper hand. This is particularly true of
brassicaceae
and
chenopodiaceae,
whose
speed of growth is greater when conditions do
not favour growth. It should be noted that late
developing varieties, and in particular dioe-
cious varieties, are most vigorous at the start of
vegetation and cover the ground more rapidly
(LCDA/SPC 1999 tests). No herbicide is
approved for use on hemp crops. Even where
trials undertaken by the FDGEDA de l'Aube
and the FNPC have found evidence to support
the use of a solution to these early problems, it
is recommended that the risk be minimized by
practising a false sowing and sowing in soil that
has been sufficiently warmed up in order to
allow the hemp to overtake the weeds.
The preceding chapter provides details of
the herbicides tested by the FDGEDA de l'Aube
and the FNPC since 1989 (Table 5.8).
Infestations of broomrape (
Orobanche
ramosa
) are a recurring problem in most
production areas (the Loire valley, Champagne
Crayeuse, Haute Saône). No solutions cur-
rently exist to deal with this chlorophyll-free
Quantity of seed sown.
The quantity of seed,
and therefore the density of the crop, must be
adapted to the objectives set. It is common to use
a sowing density of between 35 and 80 kg/ha.
Trials undertaken in the Champagne area
(AVPA Haute Marne 1985 and confirmed by
FDGEDA Aube and ITC) demonstrate that the
amount of dry matter produced per hectare
does not differ for densities as far apart as
30-300 plants/m
2
. For the lowest densities,
there is a tendency to favour the production of
hemp seed. The morphology of the plants is
also very different, in particular at the level of
the stems: these can become as wide as 3-4 cm
and develop branching that is not favourable to
fibre production. Finally, a low density favours
greater growth, producing taller plants that may
develop problems during the vegetative phase.
In particular, losses may be seen following large
storms and during harvesting where the hemp
seed is collected using a combine harvester
according to the 'French method'.
The weight of 1000 seeds is typically
somewhere in the region of 15-17 g. There
is no relation between the size of the seeds,
