Element for above-ground cultivation

The invention relates to techniques for above-ground cultivation, and, more precisely, cultivation elements designated with the name of "substrate". The cultivation cubes according to the invention are comprised of mineral fibers that are interconnected and whose distribution is without preferred order, no matter what direction they are viewed from. The substrates according to the invention promote better colonization of the material by the roots.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to techniques for above-ground cultivation (i.e., 
soil-less cultivation). More precisely, the invention relates to 
techniques in which cultivation employs several successive growth stages 
of the plants, each stage leading to the utilization of a substrate which 
offer a greater volume than that of the preceding one, to allow 
satisfactory development of the root system of the plant. 
2. Discussion of the Background 
In intensive modes of above-ground cultivation, good management of the 
materials and of the available space results in a succession of stages 
corresponding to the use of specific substrates. 
The most common method currently in use in above-ground cultivation in 
greenhouses thus has at least two successive stages. The first stage 
corresponds to the initial growth of the plants. Since this does not 
require much volume and demonstrates limited development of the root 
system, professionals prefer to use a substrate with limited volume for 
this stage. This makes it possible to multiply the number of plants 
cultivated on a limited space. This also makes it possible to minimize the 
volume of nutrient solution necessary to keep this substrate in a 
condition that is adequate for the development of the plants. In a second 
stage, the plant which have grown on these substrates with limited volume 
are arranged, together with the first substrate, on a second substrate 
which offers a greater volume, and are ordinarily spaced apart from one 
another. 
SUMMARY OF THE INVENTION 
The invention relates to mineral substrates on which plants which only 
require a limited volume, on the order of 1 square decimeter, are 
developed. More precisely, the invention relates to substrates of mineral 
fibers such as those which comprise glass wool or rock wool. 
The substrates considered according to the invention have a shape that is 
generally a parallelepiped. This shape is the one that, from the point of 
view both of the producers and the users, is by far the most practical. 
Transport of these substrates, by avoiding any lost volume, is improved by 
this shape. Their production is also greatly facilitated and lends itself 
to high-speed automation. These advantages are very important for products 
which necessarily have to be sold at a very low price. For the use, the 
parallelepiped shape allows easy grouping of these elements on a reduced 
surface in the stages of cultivation during which it is advantageous to 
minimize the space used, since the plants are not very developed yet. 
To make the presentation easier, we will designate substrate elements with 
the name of "cubes" in the following, with the understanding that they do 
not necessarily, or even generally, present a truly cubic shape. This name 
was chosen, however, because it is the one generally used by the users of 
the inventive material. 
It is necessary, in order to have a good understanding of the problem which 
the invention proposes to resolve, to explain the cultivation conditions 
in these "cubes" in greater detail. 
In the methods of intensive cultivation which represent the major markets 
for the type of products which the "cubes" represent, these are first 
arranged one up against the other, on a large surface. In this type of 
arrangement, it is necessary to provide satisfactory irrigation and, at 
the same time, suitable aeration to assure the most complete and rapid 
possible growth of the plants. The irrigation can be carried out either on 
the upper part of the cubes, or at their base, in other words the part 
which rests on the ground. These types of irrigation operations are 
carried out in a cycle which depends both on the type of cultivation in 
question and on the ambient conditions (season, temperature, evaporation, 
etc.). After a certain development of the plants, it is usual to separate 
the cubes from one another to offer more space and light. In this stage 
again, irrigation is advantageously carried out as indicated above, a 
method which is designated with the term of "subirrigation." 
In these stages of cultivation in cubes, we have seen how irrigation can be 
carried out. Good aeration is a necessary condition for good development 
of the latter. 
While aeration of the cubes depends on the irrigation conditions, it 
depends above all on the cubes themselves. 
Devices have been proposed elsewhere to improve aeration of the cubes, by 
changing their shape, for example. In these prior devices, the basic aim 
is to prevent too large a contact surface between the cubes and the 
support on which they rest. The purpose is therefore essentially to 
promote "drainage" of the cube. In other words, starting with a material 
for which the water retention characteristics are known, what is involved 
is to change the shape of these cubes in such a way as to change the 
"usual" characteristics of these materials. 
A difficulty encountered with prior cubes is not only to end up with a good 
air/water ratio, but also do work in such a way that this ratio is 
maintained for as long a time as possible between two batches of solution, 
if the solution is supplied in discontinuous manner. Furthermore, it is 
important to limit the differences which can exist between different 
levels in the height of the cube, to the greatest possible extent. 
It has been proposed previously to use cubes in which the fibers are 
preferentially oriented in planes that are essentially vertical, in order 
to prevent the formation of a part at the base which is entirely 
saturated, for example. With the same packing comprising the base 
material, the distribution of the solution will be very different, 
depending on whether the fibers are in horizontal or vertical planes. 
Furthermore, the use of cubes with vertical fibers will give the cubes a 
better mechanical hold, particularly better resistance to crushing. This 
property is particularly desirable if felts (mats) with a relatively low 
volume weight are used, which corresponds to thinner fibers, which offer 
less resistance to deformation under cultivation conditions. 
DESCRIPTION OF THE INVENTION 
However, experience has shown that the choice of materials in which the 
fibers are mainly in vertical planes is not fully satisfactory for the 
needs of horticulturists. It has been shown, in the course of study of 
these materials, that the mechanical strength and the air/water ratio, 
although they are very great, do not completely take the needs for plant 
growth into account. The inventors have been able to show that the 
distribution of the roots in the cultivation material is a very 
influential factor, and that this distribution needs to be improved. 
While the growth of plants in cubes with "vertical" fibers is promoted by 
better drainage and therefore by the existence of a higher air/water 
ratio, the verticality of the fibers seems to limit the diffusion of the 
roots in the cube. In a simplified manner, the growth of the roots occurs 
preferentially from the top to the bottom in this type of cube, with 
limited transverse colonization. The reasons for this form of growth are 
not fully determined. We will attempt some hypotheses further on, looking 
at results for comparison examples compared with embodiments according to 
the invention. 
The inventors have shown that for cultivation cubes made of mineral fibers, 
it was possible to improve the colonization of the material by the roots 
without thereby causing difficulty with regard to mechanical properties, 
by using a felt which has a structure different from that of the most 
usual felts. 
In this regard, it is known that the mineral fiber substrates used in 
above-ground cultivation are products diverted from their original 
intended use, which is thermal insulation. In practice, the industrialists 
who had the idea of using these products in horticulture initially limited 
the modifications of the base product to the strict minimum, which was to 
make them wettable, while traditionally, hydrophobic properties are 
desirable for insulation. The method of production for the felt used for 
production of the substrates for above-ground cultivation is the same as 
that for insulation felts, for this reason; this applies particularly to 
the formation of the fibers and the subsequent stages which result in 
composition of a felt. It is well known that in the usual modes of 
production, the fibers collected on a conveyor that is gas permeable have 
a tendency to place themselves in parallel layers, in the plane of the 
conveyor on which they are deposited. This preferential orientation, which 
is inherent to the production techniques, is found in the final product. 
In the case of substrates which are said to have "vertical fibers," the 
structure of the base material remains unchanged. Only the position of the 
material in the substrate is modified. Instead of being used as a 
"horizontal" felt, the felt is used vertically, by rotating the material 
in the cultivation elements. Therefore, in this case, the layers which 
initially form parallel to the plane of the receiving conveyor are in a 
"vertical" position. 
The inventors have shown that an improvement in the growth of the plants 
and better colonization of the material of the cubes could be obtained by 
using a material in which the fibers are not arranged preferentially in a 
stratified form, but, to the greatest extent possible, are oriented in a 
random manner in all directions. 
Insulating materials with a mineral felt base which present this type of 
structure are known, for example, from the European Patent EP-B-0 133 083. 
The purpose pursued in this prior document is to constitute insulation 
felts which have a very good mechanical strength, particularly resistance 
to compression, and which are used, for example, in building terraces. 
It has been shown that the felts which present a structure analogous to 
that of insulating fiber products of the state of the art cited promote an 
advantageous distribution of the root system in plant cultivation. 
The method of obtaining the substrates according to the invention also 
determines their structure. This method is the one described in the 
European patent cited. According to this patent, what is involved is to 
assure a rearrangement of the orientation of the fibers, starting with a 
nonwoven fabric of fibers collected on a conveyor belt. The fabric formed 
on the conveyor has the layers as indicated above. The rearrangement is 
carried out by compressing the fabric in the longitudinal direction. This 
operation, which is also called creping, is carried out in continuous 
manner on the fabric, before the structure is fixed by cross-linking the 
binder. 
The operation of creping, which corresponds to longitudinal compression, 
must not be confused with the compression exerted in the thickness of the 
fabric in almost all production methods for insulation packings. This 
latter process has the main purpose of fixing the thickness of the final 
product and its volume weight. Compression exerted perpendicular to the 
plane of the fiber layers does not result in any change in the 
stratification, only tightening of the layers. 
This being said, it is self-evident that longitudinal compression which 
leads to creping of the fibers can be combined with a compression in the 
thickness of the fabric, and these operations can be simultaneous or 
consecutive. 
The longitudinal compression can reach high proportions, which are a 
function of several factors: the dimensions of the fibers which comprise 
the fabric, the thickness and the volume weight of the fabric, etc. To 
obtain a significant rearrangement of the orientation of the fibers, the 
rate of longitudinal compression is greater than 1.5, and preferably 
greater than 2. 
The term "rate of compression" in understood to be the ratio of the lengths 
before and after compression. 
For fabrics which initially have a very low volume weight, and taking into 
account the volume weights used in materials for above-ground cultivation, 
the rate of compression can be as high as 10 and more. Usually, the rate 
will not exceed 6. 
In preferred manner, the cubes according to the invention have a volume 
weight between 20 and 70 kg/m.sup.3, and preferably between 30 and 60 
kg/m.sup.3. 
Economic reasons make it desirable to use the lightest products. A gain in 
material costs and also in transport costs can be achieved. Furthermore, 
light products are also often those in which the fibers are the thinnest, 
and which therefore offer the highest rates of water retention relative to 
the weight of the fibers. However, lightness must not be allowed to 
compromise the strength of the cube in use. Even suitably creped, which 
improves the mechanical strength by changing the distribution of the 
fibers, the cube must preferably not be less than 20 kg/m.sup.3. In this 
sector, cubes made of fiberglass, where the fibers can be long and thin in 
dimension, are among the products which can have the smallest volume 
weight. There is another reason why a minimum volume weight is preferable. 
It is suitable for these cubes to have a certain stability during their 
use. They are generally simply placed on the support which holds them. It 
must be prevented that the plant growing in the cube can tip it over. It 
is especially important that the cubes do not suffer any major 
deformations if compressed, and in particular, that they can be picked up, 
even when filled with solution, without deforming too much. It is 
important, in fact, that manipulations of the cubes, for example during 
thinning or placement on flats, does not cause then to come loose. A 
certain volume weight is therefore preferable. 
The dimension of the fibers is another factor that influences the quality 
of the products. Previously, in making mineral substrates, the tendency 
was to use fibers which were among the thinnest that could be made. The 
purpose was to promote the capillarity of the products by increasing the 
ratio of fiber surface/fiber weight. Experience in cultivation shows that 
to promote growth of the root system in a homogeneous manner, and for the 
preferred volume weights as indicated above, it is advantageous to choose 
fibers with an average diameter between 2 and 9 micrometers, with a 
diameter between 4 and 7 being preferred. The micron ratio of these fibers 
is between 1 and 7 on 5 g.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 represents a traditional cube. This is ordinarily composed of a 
block of mineral wool (1) with dimensions on the order of about ten 
centimeters on a side. 
Traditionally, the upper face of the cube has a recess (2) in which a 
"plug" (6) will be placed. This is the name for supports with small 
dimensions--a few centimeters--comprised of a material on which 
germination takes place at the start of cultivation. The step of growth of 
the plant by the use of a plug is not necessary. This stage is utilized by 
horticultural companies which work in very large volume. In this case, it 
allows a very significant gain in space for the first few days of 
cultivation. The plug is made of a material which can be the same as that 
of the cube, or different. 
The structure of the cube is such that the layers (3) of the fiber material 
are arranged vertically. The arrangement is ordinarily visible, to the 
extent that light variations in coloration, related to the presence of a 
binder, cause "striae" on the upper face. The same "striae" are also 
visible on the lateral faces, to which the layers are perpendicular. 
The distribution of the fibers in the "plane" of a layer appears completely 
random, in contrast. This is represented in the plane of the cross-section 
(4). It is understood that the same random arrangement is found on the two 
other lateral faces parallel to the layers, which are not shown on FIG. 1. 
The cube is generally covered with a wrapper (5) held on the four lateral 
faces. This wrapper is ordinarily made of polyethylene or any other 
synthetic film with the same properties. The film of the wrapper is 
generally held on the cube by heat-shrinking. The role of the film is to 
limit evaporation of the cube, to prevent the roots from exiting on the 
lateral faces of the cube, and to prevent growth of algae on the cube. For 
this latter reason, the material of the wrapper is advantageously opaque 
for UV light. 
The same elements are shown in FIG. 2 for a cube produced of a material 
according to the invention. The difference in treatment, in other words 
the longitudinal compression of the packing or creping, breaks the 
traditional "stratification" of the fibers. If the compression is carried 
out in a satisfactory manner, following the indications stated above, the 
structure is practically identical in all directions. This is shown in 
FIG. 2, which shows fibers without preferred orientation, no matter what 
plane is viewed. 
One of the principal advantages of the use of the cubes according to the 
invention, as compared with traditional cubes, is illustrated in FIGS. 3 
and 4. In these two figures, which each represent a quarter of a cube in 
cross-section, the typical modes of growth in each of the materials are 
shown in schematic manner. 
In the traditional material of FIG. 3, the growth of the roots takes place 
to a greater extent between the layers. The roots seem to find it 
difficult to pass from one layer to the next, as if they encountered an 
obstacle to their forward movement. Growth in the planes parallel to the 
layers promotes a rapid progression of the roots towards the bottom layers 
of the cube or on the sides. Under these conditions, colonization of the 
cube by the roots is only partial. 
In contrast, the growth of the sample according to the invention in FIG. 4 
shows good diffusion of the roots in the entire material of the cube, in 
all directions. The cube is therefore better "utilized" for its functions 
of providing air and nutritive solution to the plant. Furthermore, for 
identical cultivation periods, plants growing on the products according to 
the invention are better developed. 
In the prior embodiments, it was found that the effect of stratification 
which prevents penetration of the roots is all the more noticeable, the 
more the felt is composed of long and thin fibers which form a closer 
network. For this reason, the choice of cubes corresponding to the 
characteristics of the invention is particularly useful with glass fibers. 
Comparison tests were conducted using tomato plants of the Capello variety. 
Cultivation was carried out on cubes of glass fibers. This glass is one of 
those utilized for products intended for insulation. Its composition is: 
______________________________________ 
SiO.sub.2 64.1% Na.sub.2 15.75% 
Al.sub.2 O.sub.3 
3.4% K.sub.2 O 1.15% 
CaO 7.2% B.sub.2 O.sub.3 
4.5% 
MgO 3% Fe.sub.2 O.sub.3 
0.45% 
SO.sub.3 0.25% impurities 
0.2% 
______________________________________ 
The felts have a volume weight of 45 kg/m.sup.3 and their micronaire ratio 
is 5 on 5 g (which corresponds to fibers with an average diameter of 6 
micrometers). 
In a first series of samples, the felt was kept stratified. No longitudinal 
compression was applied during its production. 
In a second series of samples, the felt used is the result, after a 
nonwoven fabric is received on a conveyor, of one or more longitudinal 
compressions with a rate of 4. 
The cubes have a size of 100.times.100.times.65 mm. In the "laminated" or 
stratified cube, the layers are vertical. 
Cultivation was carried out as follows: 
seeding at time=0 on plugs of glass wool, 
at 2 weeks, replanting of the plugs on cubes arranged side by side, 
at 5 weeks, separation of the cubes at a ration of 8/m.sup.2 of ground, 
at 6 weeks, the plants are ready for transport of the cubes on cultivation 
flats. 
Growth is stopped at this stage. The plants are cut at a level higher than 
the cube, and the fresh above-ground vegetable weight is measured, and the 
two series of samples are dried. 
The average of 12 plants of each of the series shows the following: 
sample on stratified cube: 
fresh weight: 239 g 
dried weight: 24.1 g 
sample on cube according to the invention: 
fresh weight: 266 g 
dried weight: 27.1 g 
The comparison shows a progression of approximately 10% of the above-ground 
vegetable weight in the case of the invention. This finding is 
supplemented by the observation of the growth of roots in the 
cross-section of the cubes. It is clearly evident on the cross-sections 
that more complete colonization occurs on the cubes according to the 
invention. 
In the above, it was indicated that felts made of glass fibers are well 
suited for the intended use. Economic considerations are added to this 
result, which make these felts very advantageous in certain cases. In this 
sense, the origin of these products must be emphasized once again. We have 
seen that they were derived from the production of insulation packings. 
Taking into account the geographic distribution of production plants for 
insulation fiberglass, it is possible to produce the cultivation cubes 
according to the invention in the proximity of the utilization areas, and 
therefore to minimize costs for transport and storage.