Agriculture Reference
In-Depth Information
production is usually unaffected. Stems sec-
tioned by hailstones continue growing by devel-
oping several branches at the point of
sectioning. The quality of the hurds is altered
and the fibres are often of poor quality.
The same is not true of hail that strikes
after the end of the vegetative phase. Excepting
shelling losses, the damage caused to the
stems, particularly if weather conditions remain
humid, can serve as entry points for disease
that are detrimental the hurds. In such cases,
the crop is virtually lost.
equally possible that the ground structure does
not allow the root system to develop suffi-
ciently. The decline in growth may be seen
early in the active growth period and the first
dead stalks at the start of flowering. An attack
by one or several pathogens can generally be
observed on these stalks, although it is usually
impossible to tell whether these have caused
the problem or whether they contaminated the
root after it went into decline.
The significance varies, but a number of
consistent elements can be identified. Thus,
the proportion affected is low where plant den-
sities are low, increasing from a density of 50
plants/m
2
, at which point 50% of the plant's
stalks may be found to be atrophied or dead.
Climatic accidents have a tendency to
amplify the phenomenon, either through
excess water or drought.
Cultivars are observed (LCDA, FNPC 1999
trials) to differ in their propensity to self-thin.
LODGING
.
Wind associated with rain can flatten
plants during their vegetative phase. In the
majority of cases, plants can right themselves
and recover. If the lower part of the stem
remains on the ground, however, this can make
reaping difficult.
Lodging during early stem elongation has
a relatively small effect on yield, as the plant
can right itself and reform the canopy.
Lodging is aggravated by good growth
conditions, particularly where stem elongation
is unusually fast. This can lead to temporary
stem weakness. This problem can be provoked
by excessive nitrogen fertilization.
6.2.2 The crop's itineraries
The crop's itineraries are determined by the
end purpose, or use, and therefore by the mar-
kets that stipulate the technical requirements to
be met. Fibre quality varies significantly as a
result of the options taken. By contrast, the
quality of the hemp hurds remains unchanged.
Thread production is the oldest market. In
SEED LOSS
.
Hemp seed is very sensitive to
seed loss (or 'shelling') by the wind. As soon as
the plant reaches maturity, the seeds dehisce
easily. The morphology of certain closely
grouped fertile heads of certain varieties (e.g.
Finola, USO) can limit this phenomenon.
The decision to harvest must take this risk
into consideration. Thus, in practice, harvest-
ing starts before all the seeds attain maturity.
This minimizes the risk of seed loss.
•
Europe, the Danube valley has preserved
its knowhow. Chinese production is ori-
ented primarily towards this market.
Paper manufacturing developed as a mar-
•
ket following the invention of printing.
This represents the main destination for
hemp fibres produced in France, with a
focus on the production of specialist
papers: Bible paper, cigarette paper and
paper for bank notes.
Plastic manufacturing is a developing mar-
SELF
-
THINNING
,
OR DEAD STALKS
.
A distinction
needs to be made between losses sustained at
the time of emergence, where seeds will not
give rise to an emerging plant, and losses sus-
tained during the growth phase.
It is normal to see a halt in the growth of
some growing points, a decline or even a pre-
mature end to the growth cycle. There can be
many causes of this phenomenon. Generally
speaking, these plants have suffered an insult
that affects their growth. Neighbouring plants
gain the upper hand and overwhelm them. It is
•
ket with mineral and/or synthetic fibres
being replaced by plant fibres. This is the
main outlet for German and English
producers.
The specifications can be summarized as fol-
lows (for more information, the reader is
referred to Chapter 9):
