Agriculture Reference
In-Depth Information
Box 9.4.
Surface area needed to store the
material produced by 1 ha of hemp.
Box 9.1.
Value by weight.
1 ha of hemp produces:
- 4-12 t of dried straw with a humidity of
15%
- 0.6-1.5 t of hemp seed
1 t of straw can be broken down into:
- 0.55-0.65 t of hurds
- 0.2-0.3 t of fibre
- 0.15 t of powder
1 ha of hemp therefore produces (based on a
yield of 8 t/ha):
- 4.8 t of hurds
- 2 t of fibre
- 1.2 t of powder
Straw:
1 ha producing 8 t of straw/year, stored as round
bales with a diameter of 1.65 m
Weighing 380 kg/bale, i.e. 21 bales/ha
Ground surface area required for one bale
= 2.14 m
2
Weight per m
2
/bale: 380 kg/2.14 m
2
= 0.177 t/m
2
Storage over five levels: 0.380 t × 5 = 1.9 t
Weight per m
2
= 0.89 t/m
2
Surface area needed for 1 ha: 4.2 m
2
(out of
circulation) with piles of 5 bales
Fibre:
Weight of a bale of fibre = 400 kg
Volume = 1.5 × 0.8 × 0.8 = approximately 1 m
3
Ground surface area required for 1 bale = 1.2 m
2
Weight per m
2
/bale = 0.330 t/m
2
Storage over 6 levels = 1.98 t/m
2
Surface area needed for 1 ha = approxi-
mately 0.5 m
2
(out of circulation)
Box 9.2.
Volumes required when storing the
derivative constituents of hemp.
1 t of straw pressed into round bales occupies
approximately 6.5 m
3
1 t of fibre pressed at high density occupies
approximately 1.9 m
3
1 t of hurds occupies approximately 5.5 m
3
1 t of powder occupies 0.5 m
3
•
to facilitate the removal of the lignified
component.
Principle
Box 9.3.
Volumes necessary to store the
material produced by 1 ha of hemp.
Retting produces a partial breakdown of pectins,
together with a degradation of hemicelluloses as
well as the interpolymer bonds of the parietal
system. This phenomenon is attributable to the
activities of pectinases and hemicellulases, as well
as to enzymes that have yet to be characterized
fully (disconnecting enzymes, oxidases, etc.).
Finally, it would appear that the extraction
and trapping of calcium by organic acids pro-
duced by microorganisms also make a signifi-
cant contribution to the retting process and
help destabilize pectins.
Obviously, these catalytic processes are
under the control of microorganisms, or a pop-
ulation of microorganisms, according to modal-
ities that remain relatively unknown to this day
and still remain to be determined.
Attempts to mimic this biological process
using enzymes or specific chemical agents fail
to reproduce the natural phenomenon. These
imperfect artificial processes may, however, be
adequate for an industry that can use these
techniques to control the fibre-removing pro-
cess and refining of hemp.
2
Straw: 6.5 m
3
× 8 t = 52 m
3
As hurds:
As fibre
As powder
The French verb 'to rett' is
rouir
. It has its
origins in the 18th century and describes the
isolation of textile fibres (from flax and hemp)
by the destruction of the sticky matrix that
binds them together. This is undertaken by
macerating them in water or by any other pro-
cedure (translation of the definition appearing
in the
Petit Robert
1984 edition).
1
Retting is defined as the fibres being bound
together and to other parts of the plant by
pectins that are insoluble in water: these sub-
stances must be broken down by a fermenta-
tion process, termed 'retting':
in order to free the fibres of the stem and
•
attack the lignified part;
