U.S. patent application number 14/313485 was filed with the patent office on 2015-12-24 for cultivation medium presenting water availability comparable to that of a peat.
This patent application is currently assigned to Florentaise. The applicant listed for this patent is Florentaise. Invention is credited to Eric Beaudet, Laurent Tournayre.
Application Number | 20150368165 14/313485 |
Document ID | / |
Family ID | 51167822 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150368165 |
Kind Code |
A1 |
Tournayre; Laurent ; et
al. |
December 24, 2015 |
Cultivation medium presenting water availability comparable to that
of a peat
Abstract
The present invention provides a cultivation medium
characterized in that it is made by defibration of a bark-based
composition comprising at least 70% by volume of bark, said
cultivation medium having water availability that is greater than
or equal to 250 mL/L.
Inventors: |
Tournayre; Laurent;
(Aubenas, FR) ; Beaudet; Eric; (Savennieres,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Florentaise |
Saint Mars Du Desert |
|
FR |
|
|
Assignee: |
Florentaise
Saint Mars De Desert
FR
|
Family ID: |
51167822 |
Appl. No.: |
14/313485 |
Filed: |
June 24, 2014 |
Current U.S.
Class: |
71/23 |
Current CPC
Class: |
C05F 11/00 20130101;
A01G 24/00 20180201; C09K 17/52 20130101 |
International
Class: |
C05F 11/00 20060101
C05F011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 20, 2014 |
EP |
14305960.8 |
Claims
1. A cultivation medium comprising a defibrated bark-based
composition comprising at least 70% by volume of bark, said
cultivation medium having water availability that is greater than
or equal to 250 mL/L.
2. A cultivation medium according to claim 1, wherein the
bark-based composition comprises at least 80% by volume of
bark.
3. A cultivation medium according to claim 1, wherein the remaining
volume of the bark-based composition is wood.
4. A cultivation medium according to claim 1, wherein the bark is
the outer bark from woody plants.
5. A cultivation medium according to claim 1, wherein the
bark-based composition comprises 100% by volume of bark, and
comprises: a fine fraction, corresponding to particles smaller than
100 .mu.m, that is less than 10%; a medium fraction, corresponding
to particles lying in the range 100 .mu.m to 1000 .mu.m, that is
greater than 50%; and a coarse fraction, corresponding to particles
lying in the range 1000 .mu.m to 10,000 .mu.m, that is less than
40%.
6. A cultivation medium according to claim 5, wherein: the fine
fraction is less than 5%; the medium fraction is greater than 60%;
and the coarse fraction is less than 30%.
7. A method of treating a bark-based composition, wherein the
bark-based composition is defibrated, said bark-based composition
comprising at least 70% by volume of bark, in order to make
cultivation media having water availability that is greater than or
equal to 250 mL/L.
8. A method according to claim 7, wherein the bark-based
composition comprises at least 80% by volume of bark.
9. A method according to claim 7, wherein the remaining volume of
the bark-based composition is wood.
10. A method according to claim 7, wherein the bark is the outer
bark from woody plants.
11. A method according to claim 7, wherein the bark-based
composition is defibrated by raising temperature and
compression.
12. A method according to claim 10, wherein the temperature and
compression are increased by means of an auger machine.
13. A method according to claim 11, comprising a step of grinding
and screening bark, in such a manner that the extruded bark-based
composition has a particle size of 25 mm to 40 mm.
14. A method according to claim 13, wherein the extruded
composition has a particle size of 10 mm to 25 mm.
15. A cultivation medium according to claim 2, wherein the
remaining volume of the bark-based composition is wood.
16. A cultivation medium according to claim 2, wherein the bark is
the outer bark from woody plants.
17. A cultivation medium according to claim 3, wherein the
bark-based composition comprises 100% by volume of bark, and
comprises: a fine fraction, corresponding to particles smaller than
100 .mu.m, that is less than 10%; a medium fraction, corresponding
to particles lying in the range 100 .mu.m to 1000 .mu.m, that is
greater than 50%; and a coarse fraction, corresponding to particles
lying in the range 1000 .mu.m to 10,000 .mu.m, that is less than
40%.
18. A method according to claim 8, wherein the remaining volume of
the bark-based composition is wood.
19. A method according to claim 9, wherein the bark is the outer
bark from woody plants.
20. A method according to claim 10, wherein the bark-based
composition is defibrated by raising temperature and
compression.
21. A method according to claim 12, comprising a step of grinding
and screening bark in such a manner that the extruded bark-based
composition has a particle size of 25 mm to 40 mm.
Description
GENERAL TECHNICAL FIELD
[0001] The present invention relates to the manufacturing of
cultivation substrates having properties, in particular water
availability, that are similar to those of peat.
STATE OF THE ART
[0002] Among cultivation media or the components of cultivation
media, peats are highly valued because of their water availability,
which represents the water that can be stored by a substrate and
that can be extracted easily by the roots of most conventional
horticultural plants. It may also be referred to by the terms
"useful storage" or "easily usable storage".
[0003] However, peats have considerable drawbacks. Peats are made
up of organic material from wetlands, frequently in fragile and
protected zones. Peats are present only in certain areas of the
world, which is problematic for shipping because they need to be
transported over long distances. In addition, their formation
process is very slow, and they thus cannot be regarded as
renewables. In addition, the extraction methods commonly used
release considerable quantities of carbon and greenhouse gases.
[0004] All of those drawbacks imply that peat-substitution
materials have been sought after for many years, and in particular
materials having water availability similar to that of peats.
[0005] Among the numerous materials that have been the subject of
studies, none have water availabilities comparable to those of
peats, e.g. in the range 250 milliliters (mL) to 400 mL per liter
(L) of substrate.
[0006] Water availability, expressed as the ratio of the volume of
water over the volume of cultivation medium, corresponds to the
water released at capillary capacities in the range -1 kilopascal
(kPa) and -10 kPa; measurement is performed using the methodology
defined in the standard EN 13041 with suction of 10 centimeters
(cm) and a water height of 100 cm.
[0007] Several methods of treating wood shavings and chips have
thus been proposed in order to obtain such water availability
values, but without success. Although the substrates obtained have
relatively high water retention, their water availability remains
insufficient, and other properties such as porosity and air content
are promoted.
[0008] Ground and screened bark-based substitutes have also been
proposed, in order to make use of the advantages of barks compared
to wood, namely greater resistance to biodegradation, and greater
water retention. Bark is thus generally ground and screened to
obtain particle size fractions lying in the range 0 millimeters
(mm) to 40 mm, which makes it possible to obtain advantageous
drainage and aeration capacities, but remains insufficient in terms
of water availability.
[0009] Fine grinding of bark has been proposed, but poses problems
in terms of controlling and reproducibility of particle size, and
in terms of macro pores becoming clogged because of the finest
particles migrating during cultivation.
[0010] Composting barks makes it possible to improve the resulting
water availability, but without making it possible to reach values
close to those of peats. In addition, composting is a process
presenting several drawbacks, among which mention may be made of: a
stock immobilization over a considerable period; losses of organic
matter; non-reproducibility; and the need for dedicated
infrastructures requiring considerable investment.
[0011] Document FR 2 900 923 describes a method of obtaining a
cultivation medium using bark. Although, that document describes
the acquisition of advantageous characteristics: pH; high
absorption capacity; and low apparent density; those
characteristics are common to numerous materials used for making
cultivation media, and the method described in that document does
not mention the water availability values.
PRESENTATION OF THE INVENTION
[0012] The present invention thus aims to provide a cultivation
medium having water availability that is comparable with the water
availabilities of peats.
[0013] To this end, the present invention provides a cultivation
medium characterized in that it is made by defibration of a
bark-based composition comprising at least 70% by volume of bark,
said cultivation medium having water availability that is greater
than or equal to 250 millimiters per liter (mL/L).
[0014] The bark-based composition typically comprises 100% by
volume of bark, and comprises: [0015] a fine fraction,
corresponding to particles smaller than 100 micrometers (.mu.m),
that is less than 10%; [0016] a medium fraction, corresponding to
particles lying in the range 100 .mu.m to 1000 .mu.m, that is
greater than 50%; and [0017] a coarse fraction, corresponding to
particles lying in the range 1000 .mu.m to 10,000 .mu.m, that is
less than 40%.
[0018] In a variant; [0019] the fine fraction is less than 5%;
[0020] the medium fraction is greater than 60%; and [0021] the
coarse fraction is less than 30%.
[0022] The bark-based composition comprises at least 80% by volume
of bark.
[0023] The remaining volume of the bark-based composition is
typically wood.
[0024] By way of example, the bark is the outer bark from woody
plants.
[0025] The invention also provides a method of treating a
bark-based composition, in which the bark-based composition is
defibrated, said bark-based composition comprising at least 70% by
volume of bark, in order to make cultivation media having water
availability that is greater than or equal to 250 mL/L.
[0026] The bark-based composition comprises at least 80% by volume
of bark.
[0027] The remaining volume of the bark-based composition is
typically wood.
[0028] By way of example, the bark is the outer bark from woody
plants.
[0029] The bark-based composition is typically defibrated by
raising temperature and by compression, e.g. by means of an auger
machine or any other device or method.
[0030] The method may also include a step of grinding and screening
the bark-based composition, in such a manner that the bark-based
composition to be extruded has a particle size of 25 mm to 40
mm.
[0031] In a variant, the composition to be extruded has a particle
size of 10 mm to 25 mm.
PRESENTATION OF THE FIGURES
[0032] Other characteristics, aims and advantages of the invention
appear from the following description, which is purely illustrative
and non-limiting, and that should be read with reference to the
accompanying drawings, in which:
[0033] FIG. 1 is a diagram showing an example of a method according
to an aspect of the invention.
[0034] FIGS. 2 to 4 show an example of an installation for
performing a method according to an aspect of the invention.
[0035] In all of the figures, elements that are the same are
identified with identical numerical references.
DETAILED DESCRIPTION
[0036] FIG. 1 is a diagram showing an example of a method according
to an aspect of the invention.
[0037] In an optional first step S1, the bark is ground, the bark
typically being from conifers.
[0038] In an optional second step S2, the ground bark is screened
in such a manner as to obtain bark presenting a determined particle
size. It is thus sought to obtain a bark comprising particles lying
in the range 5 mm to 40 mm. The bark typically presents particle
size of 25 mm to 40 mm, or particle size of 10 mm to 25 mm. This
optional second step S2 may be performed following the optional
first step S1, and may also be performed independently of the
optional first step S1.
[0039] In a third step S3, a bark-based composition is formed. The
bark-based composition is formed by bringing together bark,
typically bark from conifers, which is then typically combined with
wood, e.g., wood chips or shavings.
[0040] The bark forms at least 70% by volume of the bark-based
composition, or by way of example, at least 80% by volume, or even
more precisely at least 90% by volume of the bark-based
composition, or even at least 95% by volume of the bark-based
composition. The remaining volume of the bark-based composition is
typically wood.
[0041] The bark-based composition may be constituted by 100%
bark.
[0042] Other types of bark may be used. As a function of the nature
of the bark, for example for hardwood bark, it may be necessary to
perform a preliminary step of phyto-toxicity treatment.
[0043] In a variant, the optional grinding as well as the optional
screening may be performed after the step S3 of forming the
bark-based composition.
[0044] In a fourth step S4, the bark-based composition is
defibrated, e.g. by extrusion by means of a machine, typically an
auger or worm-screw machine, in such a manner as to compress and
raise the temperature of the bark-based composition.
[0045] An example of a machine that may be used to perform said
defibration is presented below, it being understood that
defibration may be performed by means of other machines or
methods.
[0046] FIGS. 2 to 4 show an example of a machine making it possible
to implement a method according to an aspect of the invention.
[0047] FIG. 2 is a diagrammatic plan view of a defibration
installation making it possible to implement the method of the
invention, with the wall of the sheath being cut-away.
[0048] FIG. 3 is a diagrammatic view corresponding to a view of the
FIG. 1 installation in section on plane II-II of FIG. 2, with the
portions of the screw 14 that are present in this plane being
omitted.
[0049] FIG. 4 is a view in section on line III-III of FIG. 2.
[0050] The installation shown in the figures comprises a sheath 10
in which two screws 12, 14 are disposed that mesh with each other,
thus forming an auger extrusion machine. The distance e between the
axes of the two screws is less than the outside diameter of their
threads. The shafts 12A and 14A of the screws 12 and 14 are driven
in rotation by a motor M and are mediumed in rotation by bearings,
such as the bearings 15.
[0051] As can be seen more clearly in FIG. 4, the outside wall of
the sheath has the shape of two intersecting cylinder segments,
each of which is adapted to match the diameter of the screws 12 and
14. Preferably over its entire length, the sheath has an opening
cover that forms one of its longitudinal walls and serves to enable
maintenance and jam-clearing to be performed on it, if
necessary.
[0052] The bark-based composition 16 that is to be defibrated, i.e.
reduced to fibers, is loaded into the sheath via a feed 20 situated
at the upstream end 10A of the sheath and, for example, being in
the form of a hopper situated on the top face of the sheath, into
which the bark-based composition is brought by any suitable means,
e.g. by a screw conveyor (not shown).
[0053] At its downstream end 10B, the sheath has an outlet 22. For
example, the outlet is constituted by a chute situated on the
bottom face of the sheath and allowing the fibers 24 to fall by
gravity onto the belt conveyor 26. The conveyor may be equipped
with a tunnel (not shown), ventilated with a gas, such as air
(preferably filtered air), so as to cool the fibers progressively
as they are being conveyed.
[0054] The opening in the wall of the sheath that is formed at the
feed 20 is advantageously symmetrical about the vertical midplane
between the axes 12A and 14A of the screws so as to guarantee good
distribution of the bark-based composition onto the two screws as
soon as said chips enter the sheath. Similarly, the opening formed
at the outlet 22 of the sheath is advantageously symmetrical about
the same vertical midplane.
[0055] Due to the rotation of the screws, the bark-based
composition is driven in the direction S going from upstream to
downstream.
[0056] One or more extraction filters 28 are disposed in the bottom
wall of the sheath, which filters serve to extract the liquor
coming from the defibration or the water for washing the bark-based
composition, thereby making it possible to regulate the final
humidity of the product. For example, said filters are placed at
the upstream ends of the braking zones that are described
below.
[0057] The two screws 12 and 14 turn in the same direction R and at
the same speed of rotation. Over each segment of the facing screws,
the threads of the two screws are of the same direction.
[0058] For each screw, the threads have an upstream series SM of
segments and a downstream series of segments SA. In this example,
the threads also have an intermediate series SI situated between
the upstream series SM and the downstream series SA. Thus, the
series SM, SI, and SA are disposed in succession along the sheath
from upstream to downstream.
[0059] Each of the series itself comprises a drive upstream zone,
respectively SME, SIE, and SAE for the upstream, intermediate, and
downstream segments, and a braking downstream zone, respectively
SMF, SIF, and SAF for the upstream, intermediate and downstream
series. These drive zones and braking zones are respectively
referred to as "upstream" and as "downstream" because, for each
series, the drive zone is upstream from the braking zone in the
direction S in which the bark-based composition advances during
defibration.
[0060] It can be seen that, in the drive zones SME, SIE, and SAE,
the threads 12B and 14B of the screws 12 and 14 are forward
threads. This means that, by turning the screw in the direction R,
these threads cause the material that is situated between them to
advance downstream naturally. Conversely, in the braking zones SMF,
SIF, and SAF, the threads 12B and 14B are reverse threads, i.e.
turning the screw in the direction R tends to cause the bark-based
composition situated between them to move back upstream.
[0061] As a result, for each series, the bark-based composition
being defibrated tends to clump together at the interface between
the drive zone and the braking zone. In order to enable the
bark-based composition to be conveyed, nevertheless, downstream
through each braking zone, the threads of the braking zones have
interruptions or notches 12C, 14C. Thus, these notches form
constriction zones through which the bark- based composition is
forced to pass, under the effect of the thrust exerted, upstream,
by the bark-based composition driven downstream by the drive
upstream zone.
[0062] The bark-based composition is subjected to a rise in
temperature as a result of the pressure exerted inside the
extruder, which pressure may in particular be regulated by the
number of notches in the braking zones and by their dimensions. Due
to the effect of the increase in temperature, of pressure, and of
friction, the bark breaks up and retains only the primary
structures making it up, thus performing defibration.
[0063] The notches can be seen more clearly in FIG. 4 that is a
view in vertical section immediately upstream from a braking zone
(in this example, the braking zone of the upstream series SM), and
shows how a braking zone is organized. In this example, for the
braking zone of each of the two screws 12 and 14, each thread has 5
identical notches, respectively 12C and 14C, that are uniformly
angularly distributed.
[0064] The axes of the screws are referenced 12A and 14A, which are
the axes of rotation of their carrier shafts, respectively 12P and
14P. Since the screw segments can advantageously be disassembled,
their threads are carried by sleeves, respectively 12M and 14M,
which are mounted on the carrier shafts and are constrained in
rotation therewith by any suitable means, e.g. by axial fluting
(not shown).
[0065] For each thread, the notches are defined radially between
the radially outer periphery of the thread and its radially inner
periphery defined by the outside surface of the sleeve,
respectively 12M and 14M. For example, the outside diameter of each
screw, defined by the radially outer periphery of its thread, is
240 mm, the radial height h of a notch is 44 mm and the width of a
notch is 16 mm. For a thread, i.e. by following a thread of the
screw through an angle of 360.degree., a sum of the sections of the
notches of the thread is obtained that is as follows:
5.times.44.times.16=3520 square millimeters (mm.sup.2).
[0066] Advantageously, in a braking zone of the screw 12 or 14, the
notches 12C or 14C of two consecutive threads of the same screw are
angularly offset to a small extent. In order to illustrate this
characteristic, in FIG. 3 thick lines are used to show the notches
in the threads that are situated firstly starting from the section
plane, while thin lines are used to show the positions of the
notches in the threads that are situated immediately downstream
from the first threads. In this example, the angular offset is
approximately in the range 10.degree. to 20.degree., and it is
directed in the direction of rotation R of the screws, so that a
line interconnecting two corresponding notches of two adjacent
threads is directed in the same direction as the forward
threads.
[0067] The installation is fed continuously and the feed flow-rate
is adjusted to satisfy pressure and temperature parameters.
[0068] Thus, the installation advantageously includes at least one
temperature sensor CT situated upstream from the downstream braking
zone SMF of the upstream series (in the region of the section plane
III-III). A correspondence table giving correspondences between
temperature and pressure may be established. Thus, a rise in
temperature revealed by the temperature sensor CT can indicate too
high a risk of an increase in pressure. The installation can then
by regulated by reducing the bark-based composition feed flow-rate.
It is also possible to make provision for the pressure to be
measured directly by means of a pressure sensor CP situated in the
same region as the temperature sensor CT. The measurements made by
these sensors (at least the measurement made by the temperature
sensor CT) may be input into a microprocessor that delivers a
command to the bark-based composition feed system, e.g. an auger,
as indicated above. If no direct pressure measurement is available,
the microprocessor may, in a memory, have a temperature/pressure
correspondence table. If the pressure is measured directly, the
microprocessor can control the bark-based composition feed system
on the basis of the two items of data (temperature and pressure)
that are delivered to it. For a determined bark-based composition
and for a known humidity, it is possible to establish a
relationship between the pressure & temperature parameters and
the electrical power consumed by the motor that drives the screws
in rotation (or the electrical current delivered, if the voltage is
constant, as it often is). This relationship can be determined
empirically by testing. With this relationship being known, it is
possible to obtain the desired pressure and temperature parameters
by adjusting the bark-based composition feed in such a manner as to
consume a target amount of power.
[0069] The Applicant has observed that the transit
time/pressure/temperature parameters are optimized if the chip feed
of the machine is managed in such a manner as to obtain a fiber
output rate such that, knowing the total section of the notches of
each thread in the downstream series SA, the ratio RSO remains
within the range 65 mm.sup.2/m.sup.-3h-1 to 85 mm.sup.2/m.sup.3h-1,
and preferably within the range 75 mm.sup.2/m.sup.3h-1 to 85
mm.sup.2/m.sup.3h.sup.-1. It has also been observed that
defibration of bark requires less energy than defibration of wood.
By way of example, defibration of bark requires in the order of 80
kilowatt-hours per metric tonne (kWh/t) whereas defibration of wood
requires in the order of 120 kWh/t.
[0070] Naturally, the adjustments of the installation and of the
method may be fine-tuned as a function of the bark-based
composition that is defibrated.
[0071] An installation is described above that has two parallel
screws turning in the same direction and at the same speed in the
sheath. It is possible to use a different number of parallel
screws, e.g. four such screws.
[0072] Several tests have been performed with various bark-based
compositions, which tests are described below as non-limiting
examples.
[0073] As a reference value, consideration is given to the water
availability of white peat, which is 375 mL/L, and of black peat,
which is 282 mL/L.
Tests with a Composition Based on Scots Pine (Pinus
sylvestris).
[0074] The extrusion by means of an auger machine of a composition
comprising 100% Scots pine bark of 10 mm to 25 mm gauge made it
possible to obtain water availability of 369.1 mL/L, i.e. water
availability that is substantially equal to that of white peat.
[0075] The extrusion by means of an auger machine of a composition
comprising 90% by volume Scots pine bark of 10 mm to 25 mm gauge
and 10% by volume of wood shavings made it possible to obtain water
availability of 256.1 mL/L, i.e. water availability that is
comparable to that of black peat.
Tests with a Composition Based on Maritime Pine (Pinus pinaster)
and black pine (Pinus nigra).
[0076] The extrusion by means of an auger machine of a composition
comprising 100% maritime pine bark and black pine bark of 10 mm to
25 mm gauge made it possible to obtain water availability of 346
mL/L, i.e. water availability that is substantially equal to that
of white peat.
[0077] The extrusion by means of an auger machine of a composition
comprising 80% by volume maritime pine bark and black pine bark of
10 mm to 25 mm gauge and 20% by volume of wood shavings made it
possible to obtain water availability of 277 mL/L, i.e. water
availability that is comparable to that of black peat. The
extrusion by means of an auger machine of a composition comprising
70% by volume maritime pine bark and black pine bark of 10 mm to 25
mm gauge and 30% by volume of wood shavings made it possible to
obtain water availability of 243 mL/L, i.e. water availability that
is comparable to that of black peat.
[0078] The present method thus makes it possible to obtain a
cultivation medium having water availability that is comparable to
that of peat, i.e. greater than or equal to 250 mL/L, which is not
possible with prior art methods.
[0079] In a variant, the method may be used to obtain water
availability that is greater than or equal to 240 mL/L, 260 mL/L,
270 mL/L, 280 mL/L, 290 mL/L, 300 mL/L, 310 mL/L, 320 mL/L, 330
mL/L, 340 mL/L, 350 mL/L, 360 mL/L, 370 mL/L, or even 375 mL/L.
[0080] Obtaining water availability that is better than with known
methods of performing wood defibration may be explained in
particular by the difference of structure between bark and wood
that is observed during particle size analysis.
[0081] Table 1 below presents the results of a particle-size
analysis of fibers resulting from a defibration method applied
firstly to bark and secondly to wood.
[0082] As the table shows, for fibers obtained by bark defibration,
the particles are concentrated in the range 100 .mu.m to 1000
.mu.m, this range of values representing about 65% of the fibers.
There is little coarse fraction, greater than 1000 .mu.m. However,
it is this coarse fraction, which is not very conducive to
retaining water, and which is very common when fibers are obtained
by wood defibration.
[0083] For fibers obtained by bark defibration, the fine fraction,
corresponding to fibers that are smaller than 100 .mu.m, is
reduced, in this example to less than 5%. However, it is this
fraction that can lead to clogging of the pores and to
characteristics changing over time. A small fine fraction as
obtained by bark defibration is therefore advantageous.
TABLE-US-00001 TABLE 1 % oversize at x .mu.m Bark Wood 0 2.0% 11.2%
100 8.5% 4.0% 160 18.8% 5.8% 315 14.9% 5.5% 500 7.9% 4.5% 630 14.2%
9.9% 1000 7.2% 6.5% 1250 13.4% 23.2% 2500 9.6% 23.9% 5000 3.5% 5.5%
10,000 0.0% 0.0%
[0084] In general, by defibrating a bark-based composition
comprising 100% bark, the particle size typically obtained is as
follows: [0085] A fine fraction, corresponding to particles smaller
than 100 .mu.m, that is less than 10%, or advantageously less than
5%. [0086] A medium fraction, corresponding to particles lying in
the range 100 .mu.m to 1000 .mu.m, that is greater than 50%, or
advantageously greater than 60%. [0087] A coarse fraction,
corresponding to particles lying in the range 1000 .mu.m to 10,000
.mu.m, that is less than 40%, or advantageously less than 30%.
[0088] Varying the quantity of wood in the bark-based composition
makes it possible to influence other properties of the cultivation
medium obtained. By way of example, increasing the quantity of wood
in the bark-based composition thus makes it possible to increase
aeration of the cultivation medium obtained. In addition,
increasing the quantity of wood in the bark-based composition leads
to a progressive reduction in water availability.
[0089] Therefore, by varying the volumes of bark and wood in the
bark-based composition, it is possible to make a cultivation medium
having the desired water availability and aeration properties.
* * * * *