Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MINERAL WOOL-BASED GROWING COMPOUNDS
The invention concerns mineral-wool based compounds used for soil-less
cultivation.
The use of mineral wool, in particular rock wool (based on volcanic
rock or slag from blast-furnaces) or glass wool in what is usually known as
soil-less cultivation, has expanded considerably in recent years. These
products display a number of very interesting features. They are relatively
inexpensive, easy to use and create favourable conditions for growth: they
are harmless to plants, provide a sterile environment and have good water
retention.
The mineral wool compounds used up to now have been products directly
derived from those used for thermal insulation. They are produced in the form
of felts with fibres held together by a resin-based binding agent. Compared
with traditional isolating felts, the major difference lies in the fact that
the compounds must be capable of readily absorbing the aqueous solutions used
for watering and feeding of the plants. To this end, it is usual to
incorporate into the compounds tensio-active agents which promote water
penetration. Apart from this possible modification, every effort has been
made, for economic reasons, to ensure that the insulation products and those
intended for soil-less cultivation are as similar as possible. This has the
particular advantage of enabling the same felt-producing equipment to be
used.
It is accepted that the method of production has a major influence on
the structure of the felt. Broadly speaking, the felts are created from
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fibres produced directly from the stretching of molten material. The fibres
are carried by currents of gas to a gas-permeable conveyor. On this conveyor,
the fibres are held in place while the gases are expelled. The felt is
progressively formed by the accumulation of fibres. Analysis shows that
within the felt the fibres are arranged in an advantageous manner in planes
parallel to the conveyor. This arrangement is favourable in felts intended
for insulation because it permits good thermal resistance.
The`horizontal' arrangement of fibres also occurs in the soil-less
growing compounds which have been produced up to the present. The compounds
are marketed and used in the form of "blocks", that is parallelepiped blocks,
the dimensions of which, and the width in particular, being determined by
cultivation techniques. Users would like to have the option of blocks whose
width might vary but could exceed 200 mm or even 300 mm. To obtain these
dimensions in felts normally produced according to the dimensions of
insulating products, the practice has been adopted of cutting the blocks in
such a way that the fibres, during use, are arranged in broadly horizontal
planes, that is approximately parallel to the ground or surface on which the
block is placed.
Furthermore, still in the area of mineral fibre compounds, there exist
on the market "cubes" or sods designed for growing seedlings. When the
seedling reaches a sufficient size, these cubes are positioned on the culture
base proper. The cubes are normally made of the same material as the base
block, but their dimensions are considerably reduced, their sides measuring
in the order of 100 mm.
Contrary to what is found in the case of the blocks, the cubes are
often prepared so that when the cubes are in use the fibres are arranged in a
broadly vertical plane. The reason for this difference has also to do with
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the way in which the cubes are produced. They are made by first cutting felts
in transverse strips, then by cutting these strips across their width to the
desired size of cube. In order to limit wastage of material, and especially
to facilitate the operation of sheathing the cubes, as will later be
explained in greater detail by reference to the attached outline drawing,
this vertical arrangement of fibres within the cube has been achieved, it
seems, without there being any noticeable influence on the cultivation
results.
The purpose of this invention is to produce a growing compound in the
form of blocks, that is, to, produce a compound in which the whole growing
cycle is completed, as opposed to cubes which allow only the cultivation of
seedlings, the compound in question having new properties which are not found
in traditional blocks and which improve growing conditions for seedlings.
The blocks as defined by the invention are composed of felts made from
mineral fibres and their distinctive quality is that the fibres stand in
virtually vertical planes when in use. It is worthy of note, as will be seen
from the examples, that this modification of arrangement of the fibres brings
about a very significant improvement in yield. The reasons for this
improvement have not yet been fully analysed. It is nevertheless possible to
link this outcome with the special characteristics noted in connection with
the `vertical' use of fibres, and particularly with the water-retaining
properties of the compounds.
Research into mineral-fibre growing compounds has concentrated
primarily on maximising their inertia and their ability to retain the water
needed for growth. Of course, it is clear that the water-content of the
compound is not the only factor to be considered if plants are to grow well.
It is equally important to ensure a good flow of air, and this requires a
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balance which is difficult to maintain satisfactorily. Keeping parts of the
compound saturated with water would seem not to favour plant growth. A study
of fibrous compounds in which the fibres are arranged horizontally would seem
to indicate the presence of an uneven distribution of water (or nutrient
solutions) in the higher parts of the block, the lower parts being the most
saturated. In these conditions, even to achieve an adequate overall solution-
content, the distribution of the solution is clearly unsatisfactory.
With the use of compounds as defined in the invention, where the fibres
are arranged in vertical planes, it is observed that the distribution of
solutions in the higher part of the compound is considerably more homogenous,
and that in particular saturation is avoided even in the lowest areas. In
other words, growing blocks as defined in the invention provide better
drainage. This improved control over the distribution of solutions does not
merely eliminate the risk of saturation, it also provides for example a more
even distribution of nutrient elements and in particular prevents local
accumulation of salts.
The tests which have been carried out also demonstrate that roots
develop and achieve easier penetration of the cube within the block. The
reason why roots spread more easily when the fibres in the block are arranged
in vertical planes probably has to do with the texture of the felts of which
they are composed. It is known that in the manufacture of the felts from
which the growing-blocks are made, the lower and upper faces form a closer-
knit network of fibres and binding-agent as a result of the `polishing' which
takes place during the formation of the material in contact with the heated
binding-agent. The result is that on both faces of the felt a kind of `crust'
appears which presents the roots of plants with a certain opposition. When,
following the process of the invention, use is made of blocks in which the
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fibres are arranged in vertical planes, these `crusts' are located on the
lateral faces of the block, which means that the obstacle to the roots is
removed in their growth through the cube towards the block.
The use of fibres arranged in vertical planes has the further advantage
of an improved mechanical performance, a factor which is all the more
significant because (the) felt has a lower ratio mass/volume. In the lightest
traditional products, for example those with a mass/volume ratio of less than
30 kg/m3 or even 20 kg/m3, the resistance to collapse is relatively low, to
the point where if they are soaked in liquid they display a certain tendency
to collapse beneath their own weight and the weight of the liquid. On the
contrary, the arrangement of fibres in vertical planes confers on the
products defined in this invention a significantly higher resistance to
compression along the line of these vertical planes. For this reason, the
products defined in this invention show no tendency to collapse even when
they have a low mass/volume ratio.
In a less crucial respect, the growing blocks as defined in this
invention also help minimise the problems encountered when the soil or
surface on which the block is placed is not perfectly horizontal. The use of
traditional compounds in which the fibres are arranged horizontally also
require a perfectly horizontal surface, in the absence of which solutions
tend to saturate the lower parts to the detriment of the upper parts, which
creates a complete imbalance in the hydration of plants. The compounds as
defined in this invention are considerably less sensitive to such variations
in levels.
The mineral fibre compounds as defined in this invention are made from
felts obtained under normal conditions. Which is to say that the felts from
which the blocks are cut have their fibres arranged in planes which are more
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or less parallel to the felts. To obtain the blocks as defined in this
invention, the cutting of the felt is managed in such a way that the narrow
faces of the parallelepiped, in plain terms its thickness, become the upper
and lower faces of the growing block.
The conditions in which the felts are produced tend to limit this
thickness. As we have indicated, the felts are obtained by collecting fibres
conveyed by a current of gases, on a conveyor which acts as a filter. To
facilitate the depositing of the fibres and elimination of the gases on which
they are carried, it is necessary to maintain a strong suction beneath the
conveyor. The energy required to provide the suction is all the greater
because it becomes increasingly difficult for the gases to filter through the
conveyor and the mass of accumulated fibres. It may be imagined that in these
conditions that economic operation of the process makes it necessary to limit
the thickness of the felt being formed on the conveyor. For this reason, but
also because when it is used as an insulating material its thickness is
determined following precisely set standards, the normal production of felt
does not exceed a thickness of 300 mm, while the more usual thicknesses are
in the range of 75, 100, and 150 mm. In the case of felts not thick enough to
make into blocks sufficiently wide to be suitable for plant-growing purposes,
the practice is of course to assemble several thicknesses by joining together
parts corresponding to the upper and lower parts of the felt. The assembly
process may involve two parts or more, according to the width required.
Clearly, it is possible to envisage any combination of elements deriving from
the same felt and therefore the same thickness, or from several felts of
varying thicknesses.
Traditional mineral fibre-based compounds are normally presented
wrapped in a sheath made of a film of plastic material. The sheath has a
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variety of functions. It protects the blocks while they are being transported
and also prevents contamination by foreign matter during transportation or
storage. It also has a role in the growing process by preventing excessive
evaporation of water or liquid fertilisers. As a rule, however, the sheath is
not kept water-tight. Small holes are pierced in it to ensure a modicum of
drainage. Notwithstanding these different functions, the sheaths used for
traditional products is relatively thin and does not need to be tight or
close-fitting. On the contrary, a certain roominess around the block is to be
preferred, to facilitate drainage.
According to the invention, it is proposed that when several
thicknesses of felt are laid together to make a block, they should be placed
inside a sheath sufficiently durable and close-fitting to ensure that the
various elements which make up the block stay securely in place. This
corseting function may be added to those, outlined above, which they have in
traditional products.
It goes without saying that if an unsheathed compound is preferred, it
would be perfectly possible to replace the sheath referred to above by means
of belts or any other kind of assembly process thus leaving free almost the
whole of the surface-face of the blocks.
When the product is to be sheathed, it would be advisable, in order to
ensure a tight fit of the sheath over the felt elements, to use a sleeve made
from a sheet of a thermo-retractable plastic material. In this case, the
elements are introduced into a sleeve slightly larger than the dimensions of
the elements which are to be inserted, and then the whole is passed through a
heat process to shrink the sheet which then clings tightly around the
elements.
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The process is described in greater detail in the following paragraphs
which make reference to illustrations (see Appendix) where:
Fig. 1 is a sketch-plan showing the arrangement of the fibres in a
traditional compound,
Fig. 2 shows in schematic form the successive stages leading to the
production of a growing cube designed for the cultivation of seedlings,
in which the fibres are arranged vertically,
Fig. 3 shows in outline the structure of a block as defined in this
invention,
Fig. 4 shows in outline the structure of a block composed of several
juxtaposed elements
Fig 5 shows the two stages which lead to the assembly of two elements
by means of a sheath made of a retractable material,
The method of cultivation in the traditional compound is illustrated in
Fig. 1. The compound (1) stands flat on the ground or another surface (not
shown) which is more or less horizontal. Plants may be grown directly in the
compound (1) but it is more usual to proceed by two stages. In the first, the
seedlings are started in cubes (2) and when they have achieved sufficient
growth for them to require a volume of supplementary compound, the cubes are
placed directly onto the compound (1) into which their roots then grow. This
method of cultivation frequently mobilizes two further elements which are not
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shown, such as feeding systems which employ liquid fertilisers, or the use of
troughs in which the compounds (1) are placed so that any surplus fertiliser
draining out may be recovered.
In Fig. 1, the compound (1) has been shown non-sheathed to demonstrate
the arrangement of fibres in traditional, that is, more or less horizontal,
planes (3). It is usual to encase blocks of compound in a sheath, as has been
described earlier.
Fig 1 again shows the cubes (2) sheathed. Por these components, the
use of some kind of protective sheeting, without being absolutely
indispensable, is very widespread, this having to do with the process by
which they are normally produced, as may be seen from Fig. 2. Fig. 2a shows
schematically a cross-section of a strip of felt (4) which has come from the
production-line. As indicated earlier, the fibres in this strip of felt are
shown following parallel planes, on the lateral faces of the strip.
The cross cutting may be carried out by means, for instance, of a
circular saw (5) as shown in the sketch, or by any other traditional
equivalent used to cut felts made of mineral fibres. The first cut of the
strip results in the production of long parallelepiped (6). These components
in the form of parallelepipeds must then be cut into smaller components.
Because of their relative fragility, the cubes, as has already been stated,
are then placed in a sheath of plastic film. The sheathing process, for
obvious reasons of convenience, has a beneficial effect on the components
(6). Sheathing also enables the cubes (7) to be kept firmly in shape when
they are produced by cutting the elements (6), as is shown in 2a. As may be
seen, these successive operations result in the production of cubes (7)
sheathed on four sides. The sheathed sides are shown as hatched areas. Both
free faces (8) are normally used for growing seedlings. Given these
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circumstances, it will be appreciated that by adopting the most convenient
technique cubes are achieved in which the fibres are arranged in vertical
planes, but this arrangement is entirely unconnected with considerations
involving cultivation itself.
Fig. 3 shows the layout and structure of a growing block (10) as
defined in this invention. The use made of this block is analogous to that
described in Fig. 1. The basic difference resides in the way that the fibres
are arranged. This has been drawn so that the vertical planes may be clearly
seen, for example, in ~9).
Fig. 3 shows a block made of a single strip obtained by cutting a felt
of sufficient thickness to create a block of the required width, the
thickness of the felt constituting the width of the block. When it is not
possible to obtain the required thickness, the method, shown in Fig. 4, is
adopted of joining several components (11, 12) together. Fig. 4 shows two
identical components combined, and it is possible in the same way to combine
components of differing thicknesses or more than two components, so that a
complete range of block-widths is achieved.
As has been pointed out above, it is possible that the faces of the
felts (4) may have a surface layer which is denser in fibres and consequently
less permeable to liquids or even to roots. If this surface layer should
prove too great an obstacle, it would be preferable to eliminate it
altogether during the assembly process as represented in Fig. 4 and at the
very least on the faces of elements 11 and 12 which are contiguous (13). It
may be eliminated by scraping, the equivalent of a cut made into the
thickness of a felt which may be carried out for example by means of suitably
positioned ribbon saws.
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When several elements (11, 12) are used to form a block, as shown in
Fig. 4, they need to be bonded together. One method of assembly is shown in
Fig. 5. Here, the two elements (11, 12) are joined together by means of a
sheath (14). To obtain a stable unit, it is recommended for example that the
sheath be made from a sheet of thermo-retractable plastic material. If this
procedure is adopted, the two elements (11) and (12) are inserted into a
sleeve (15) made of the selected plastic sheet (Fig. 5a). The insertion is
very straightforward, the cross-section of the sleeve being very wide
compared with that of the two elements combined. The whole is then passed
very briefly through a heat-treatment process and the sheath shrinks over the
elements which are consequently held tightly together (Fig 5b).
The sheath used is ordinary black or white. The colour black is
ordinarily preferred for conditions when it is appropriate to limit heat loss
in the compound. This is particularly true in the case of winter cultivation.
When, on the other hand, the compound needs to be protected against very high
temperatures, then white film is preferable.
The advantages of the growing compounds defined in this invention have
been demonstrated in tests carried out on cucumbers grown in hothouses. Tests
were carried out simultaneously in traditional blocks in which the fibres are
arranged horizontally and on blocks as defined in this invention. In both
instances, the blocks were prepared from the same rock-wool felt, the
chemical composition of which is, by weight:
SiO2 41,8% FeO, Fe2O3 0.8 %
CaO 41 % S 0.3 %
A12O3 11 % TiO2 0.4 %
MgO 3.7% MnO 0.5 %
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The ratio of mass/volume of the felt is approximately 40 Kg/m3.
The dimensions of the traditional blocks (A) and of the block as
defined in this invention (B, C) are as follows:
length width thickness
A 900 mm 150 mm 75 mm
B
C " " 110 mm
The seedlings were grown on `cubes' made of the same material as the
compound of which the blocks were made, and measuring 100 x 100 x 65 mm.
The variety used was Brucona (Bruinsma). It was sown on 10 July in the
cubes and bedded out in the blocks on 27 July, two seedlings to a block.
The blocks were arranged randomly according to a spacing principle of 1,2
seedlings per square metre.
The conditions of feeding, watering and temperature were those
traditionally observed by the research establishment. Harvesting took place
between 1-30 September.
The average of the yield resulting from the crop when harvesting was
complete was as follows:
1. number of fruit per plant:
A 12.50
B 14.25
C 14.50
that is, an increase of approximately 15% in the case of plants grown
in the block as defined in this invention.
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2. weight of fruit:
A 348.4 g
B 405.0 g
C 413.7 g
that is, an increase of the order of 17.5%.
3. weight of fruit harvest per plant:
A 4.36 kg
B 5.77 kg
C 5.99 kg
that is, an increase of the order of 35 %.
These improvements in production would seem to be explained by an
improved root-strike in the plants and this itself results from a more
favourable environment, that is, a more sympathetic substratum.
Physical observation of the blocks reveals a higher ratio of air to
water in the compounds as defined in this invention, which leads to an
improved air supply to the roots.
Analysis of the blocks after the growing cycle is completed also
reveals a more regular distribution of roots and sturdier growth in the
blocks as defined in this invention.
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