Agriculture Reference
In-Depth Information
to the uncontrollable development of self-propa-
gating weeds, especially
Chenopodium album
,
Sinapis arvensis
(wild mustard),
Orobanche ram-
ose
(hemp broomrape) and increasing plant death
due to disease.
As with all spring crops, hemp allows a
break in the autumn rotation of crops and can
therefore break the reproductive cycles of cer-
tain difficult-to-control weeds, including
Bromus strilis
(bromegrass) and
Alopecurus
myosuroides
(black grass) in cereals and
Calepina irregularis
(calepina) or
Capsella
bursa-pastoris
(shepherd's purse) in rape. For
farmers of sugarbeet, hemp can reduce the
challenge from nematodes (
Heterodera sch-
achtii
) in the ground. Finally, the absence of
pesticide use in the years when hemp is grown
allows the microflora to develop and become
functional. This promotes the development of
soil microfauna, which in turn improves the
fertility and function of the soil.
According to producers, hemp cultivation
is recommended after sugarbeet and maize,
both before and after wheat and before spring
barley.
Organic farmers appreciate hemp for its
ability to leave the ground free of weeds in the
autumn and for improving the soil's structure.
They plant hemp after a leguminous crop and
before wheat. In effect, there are many combi-
nations and hemp can find its place easily in a
crop rotation system.
The cultivation of hemp on the soils found in
the
Barrois champenois
region of France,
and particularly those soils derived from cer-
tain geological ages (such as the Kimmeridgian
or Hauterivian from the Mesozoic era), dem-
onstrates this well. The plot presents a hetero-
geneous character as a function of the
sequence of more or less wet soils and the
annual pluviometry (Fig. 6.1). The height of
hemp varies from close to zero to a normal
height over a distance of a few metres. The
same phenomenon can be seen in valleys,
close to watercourses.
A NEUTRAL PH
.
The pH of the soil should fall
between 6 and 8 for optimal results. Liming of
the soil will be required if the pH is too low.
EFFECTS OF ALTITUDE
.
Tests undertaken in 2003
and 2004 in the Trièves (a region south of
Grenoble, France) demonstrated that water
provision was a more important limiting factor
than altitude (trials limited to between 600 and
1000 m) and that mountain microclimates
could provide perfectly adequate locations for
production, providing the soil and climate were
favourable.
THE TEMPERATURE
.
Hemp's sensitivity to tem-
perature is known to a certain extent. The
zero vegetation point is situated around 1-2°C;
hemp is sensitive to frost (up to five pairs of
leaves) at temperatures below -5°C, while the
optimum temperature for vegetation is situ-
ated between 19 and 25°C. The time required
for plants to grow to 90 cm in height is
30 days at a temperature of 19°C, but
increases to 90 days at a temperature of 10°C
(van der Werf, 1994).
Based on the observations made by the
FNPC, emergence requires an accumulation of
between 80 and 100°C days; the implantation
phase (up to three pairs of leaves) requires
250°C days. The active growth phase that fin-
ishes at the end of flowering allows the produc-
tion of 1 t of hurds for 120°C days. Seed
maturity requires 40 days from the end of the
flowering stage. Thus, for a variety of average
maturity, the entire vegetative cycle requires
between 2500 and 3000°C days in order to
attain complete maturity.
Needs
Hemp can grow under all conditions and copes
well with difficult situations. It is a rustic plant
that has preserved many of its wild characteris-
tics. In particular, the farmer will sow popula-
tions rather than a pure line, as is done for
most cereals.
It is clear that results are better where the
climate is favourable and the soil provided with
the necessary factors for growth, water and
fertilizing elements. Historically, our ancestors
reserved manure for hemp crops because the
hemp fields were closest to the farmhouse and
therefore easiest to fertilize with manure and
keep an eye on.
A HEALTHY SOIL
.
Wet soils are to be avoided, as
these do not allow hemp to grow normally.
