Agriculture Reference
In-Depth Information
Retting facilitates fibre extraction. While
the quality of the fibre can remain stable for sev-
eral weeks, this is not true of the hemp hurds,
which deteriorate rapidly and change from a
white colour to a more or less dark grey, result-
ing in the loss of some of their market value
the objectives over and above the quality of the
yield is to promote as rapid and as efficient
coverage of the ground as possible in order to
avoid the development of weeds.
Low densities favour plant height. This is
particularly well illustrated by the 'border
effect', where the plants growing at the edge of
a plot are 20-30 cm taller and demonstrate
more branching.
There is no correlation between the aver-
age height of a field of hemp and its hurd yield.
Low densities have a positive effect on
hemp seed yield at the expense of the yield and
quality of hurds.
Stem diameter reduces with increasing
density.
6.2.6 Actions of different production
factors on yield and quality
Hurd yield is related to the stem diameter,
together with the density and height of the
plants that have not been smothered or fallen
victim to disease. A long and problem-free
growth period will favour these factors. Late
flowering dioecious varieties are generally
more productive than monoecious varieties, as
the period of vegetative growth is longer.
The hemp seed yield depends on the dura-
tion of the flowering period, which itself is
linked to the sowing date, to the sum of tem-
peratures and the amount of water received
during the flowering period. Monoecious varie-
ties flower earlier than dioecious varieties and
are therefore more productive.
Nitrogen
Nitrogen-rich manure must be spread so that it
is available to the plants during the rapid
growth of the vegetative phase. If fertilization is
applied too late, it will not always meet the
plant's needs during growth. The absorption of
nitrogen at the end of the vegetative phase
promotes the production of leaves, sustains the
vegetative phase and delays the end of the
cycle. This translates into difficulties in drying
the hurds, which will also make fibre extraction
more difficult.
An excess of nitrogen-rich manure
increases the risk of plants lodging during the
rapid growth phase.
Where nitrogen-rich manure is limited,
achieving the same plant mass requires warmer
growing conditions (FNPC trials, 2002).
The level of nitrogen-rich manure does
not influence the fibre level in the hurds (sum-
mary of ITC trials, 2004).
As a general rule, nitrogen-rich manure
applied at a rate of 100-120 U/ha allows the
potential of the plot of land to be reached.
1
Monoecious varieties
In Europe, almost all the hemp cultivated is of a
monoecious variety whose yield is better the
later it flowers, as this allows a longer vegetative
growth phase. By contrast, early varieties grown
in temperate climates produce a better hemp
seed yield, as maturity is attained sufficiently
early for the plant to benefit from favourable cli-
matic conditions (summary of the trials on varie-
ties from the FNPC, FDGEDA Aube and ITC).
We do not have enough experience to
allow us to draw lessons for crops grown at
lower latitudes. Hemp is a temperate climate
crop, best suited to latitudes above 35 degrees.
The covering of the ground or 'canopy'
improves the later flowering variety (trials
FDGEDA Aube, 1999).
6.3
Hemp Growing and Processing
Innovation in Australia
Density
6.3.1 Overview
The seeding rate is similar from one region to
another for the same use, varying between 45
and 50 kg/ha for monoecious varieties. One of
The hemp fibre industry will succeed or fail on
its ability to provide a constant supply of
