Substrate for out-of-ground cultivation

A substrate of limited dimensions consisting of mineral fibers for out-of-ground cultivation is used for the cultivation phase corresponding to the development of seedlings. This substrate, of general parallelepipedic shape, exhibits small surface protuberances on its lower face which separate it from the ground on which it rests. The protuberances can be feet disposed on the lower face of the substrate, or edges formed by providing the substrate with a concave lower face. The substrate according to the invention makes it possible to improve out-of-ground cultivation conditions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to substrates used in out-of-ground cultivation 
techniques. More precisely, the invention relates to substrates used in 
cultivation techniques that employ successive stages of growth of the 
seedlings, with each stage leading to the use of a substrate offering a 
volume greater than that of the preceding one to make possible a 
satisfactory development of the rooting system of the seedling. 
The invention also relates to mineral substrates on which the seedlings are 
developed calling for only a limited volume on the order of magnitude of 1 
liter. More precisely, the invention relates to substrates of such mineral 
fibers as those consisting of glass wool or mineral wool. 
2. Discussion of the Background 
In intensive methods of out-of-ground cultivation, good management of 
materials and of available space leads to a sequence of stages 
corresponding to the use of specific substrates. The most widely used 
method at present in out-of-ground cultivation in the greenhouse comprises 
at least two successive stages. The first stage corresponds to the initial 
growth of the seedlings. As the seedlings are not very large and exhibit 
limited development of the rooting system, a substrate of restricted 
volume is preferred at this stage. This makes it possible to increase the 
number of seedlings cultivated in a limited space. This also makes it 
possible to minimize the volume of nutritive solution necessary to 
maintain the substrate under suitable conditions for the development of 
seedlings. 
In the second stage, the seedlings which have grown tall on these limited 
volume substrates are placed, along with the first substrate, on a second 
substrate offering a larger volume, and ordinarily spaced from one 
another. 
In the methods of intensive cultivation which represent the most 
significant prospects for this type of product substrates are used having 
a cubic shape and will hereinafter be referred to as "cubes". The cubes 
are placed against one another, in a first step, on a wide surface. In 
this type of arrangement, it is necessary to provide both satisfactory 
irrigation and suitable aeration to assure the most complete and the 
quickest growth of the seedlings. The irrigation can be performed either 
from the upper part of the cubes, or from their base, i.e. the part 
resting on the ground. In practice, the two irrigation methods can be 
combined. 
Often, the cubes are placed in a unit which forms a sort of tank capable of 
receiving enough irrigation solution to partially submerge the cubes. The 
solution rises to a sufficient level relative to the height of the cubes 
so that the cubes are completely saturated. For cubes of ten centimeters 
or so in height, the temporary level of the irrigation solution reaches, 
for example, a third of the height of the cube. The solution then rises in 
the substrate by capillary action. With this irrigation performed, the 
irrigation solution is drained and recovered for a later operation. This 
type of irrigation operation is repeated at a frequency depending both on 
the cultivation being considered and the ambient conditions, season, 
temperature, evaporation, etc. 
After a certain development of the seedlings, it is normal to separate the 
cubes from one another to offer more space and light. At this stage also 
the irrigation is advantageously performed as indicated above, a method 
that is designated by the term "subirrigation." 
In these two stages of cultivation in cubes, it was pointed out that it was 
necessary to assure good aeration of the roots between the successive 
irrigations. This aeration is a necessary condition to good development of 
the roots. The traditional cubes used exhibit a level base resting 
completely on the ground or, more exactly, on the bottom of a tank or on a 
covering, most often an impermeable film covering the ground and 
separating the cubes from the ground. In all these applications, a 
difficulty arises. The lower face of the cubes tends, in contact with the 
support on which it rests, to maintain a liquid film after the irrigation 
has stopped. In other words, when the irrigation solution is evacuated, 
whether the solution has been introduced by subirrigation or by irrigation 
through the upper face of the cubes, the contact between the cube and its 
support maintains, by what can be named a surface effect, a continuous 
liquid film which is opposed to the normal drainage of the cube under the 
effect of gravity. Under these conditions, water retention is extended 
substantially, resulting in the establishment of an unfavorable air/water 
ratio. 
To reestablish a quick drainage of the solution after each irrigation 
operation, a technique developed by the users has been to place under the 
cubes a porous material or slatted floors which eliminate this surface 
effect by breaking the contact between the cubes and their support. These 
means, however, have the drawback of complicating the maintenance of the 
cultivation areas. In particular, they must be sterilized between each new 
cultivation. 
Another solution used consisted of making grooves on the lower face of the 
cubes. These grooves, which are on the order of 1 to 2 centimeters in 
depth and width, divide the film in a way which improves the drainage and, 
as a result, the aeration of the cubes. These grooves make possible the 
reduction of the surface of contact by about one third and the return to a 
suitable air/water balance in an appreciably shortened period after each 
irrigation. A surface consistently in contact with the support also 
remains, however, at the base of the cube, and, although very small, the 
underlying liquid film remains present at these points of contact. 
SUMMARY OF THE INVENTION 
Accordingly, one object of this invention is to provide a substrate without 
the aforementioned problems. 
Another object of this invention is to improve out-of-ground cultivation by 
minimizing the effect of a liquid film which can form on the bottom of 
substrates used in out-of-ground cultivation. 
A further object is to provide a substrate having a small ratio of contact 
area to bottom surface area. 
These and other objects of this invention are accomplished by using 
substrates of general parallelepipedic shape. This shape is that which 
those skilled in the art will appreciate as the most practical. 
To meet the objects of the invention, the substrates exhibit, on their 
lower face, protuberances on which, in use, the substrates rest. The 
protuberances are advantageously of the same material as that of which the 
substrate consists. The surface of contact of these protuberances with the 
support on which they rest remains less than a tenth of the total surface 
of the total base of the substrate and, preferably, less than a twentieth. 
The shape of the protuberances is chosen principally as a function of 
convenience taking into consideration the particular embodiment. 
The protuberances break up the continuity of the contact of the lower face 
of the substrate with the support upon which it rests. This results in 
minimizing the extent of a liquid film formed on the lower face of the 
substrate during irrigation of the substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein like reference numerals designate 
identical or corresponding parts throughout the several views, and more 
particularly to FIG. 1, a prior art "cube" 10 which is of traditional 
shape for the glass wool or mineral wool substrates is shown. Its 
dimensions, are, for example, a square base of 120.times.120 mm and a 
height of 75 mm. 
The transport of these substrates, by the ability to closely pack the 
substrates is improved by minimizing lost volume. Their production also is 
facilitated greatly and lends itself to advanced automation. These 
advantages are very appreciable for products which must necessarily be 
offered at very low prices. 
The parallelepipedic shape makes possible the convenient groupings of these 
elements on a small surface in the stages of the cultivation where it is 
advantageous to minimize the surface occupied, such as when the seedlings 
are in the early stages of development. 
For the convenience of the disclosure, we will designate below these 
elements of substrates under the name "cubes," it being understood that 
they do not necessarily, nor even generally, exhibit a truly cubic shape. 
This name nevertheless is chosen because it corresponds to that which is 
ordinarily used by those skilled in the art. 
The substrates according to the invention for the cultivation of the 
seedlings, are of parallelepipedic shape exhibiting, in their use, a 
surface of contact with the support on which they rest reduced to the 
necessary minimum required for their stability. 
The materials of the cubes, whether they are glass fibers or mineral 
fibers, are chosen sufficiently "rigid" so that they do not deform 
appreciably under the effect of their own weight, even when they are 
saturated with irrigation solution. This is obtained by choosing felts 
whose density is sufficient on one hand and whose structure reinforces the 
rigidity. 
In particular, the dominant orientation of the fibers can be chosen to 
improve the resistance to crushing. It also is possible to make these 
felts more resistant by a more homogeneous tangling of the fibers. The 
dimensions of the fibers (diameter, length) also can be chosen, to a 
certain extent, according to the known principles to determine the 
mechanical characteristics in the separation applications of this type of 
felt. 
Referring again to FIG. 1, the prior art cube, on its upper part, generally 
includes a cavity 12 to receive either a previously germinated seed on a 
support whose shape corresponds to that of the cavity, or a seed directly. 
In the largest farms, it is normal to initiate the germination separately, 
which saves space and improves the profitability of the installations by 
reducing the time the available surfaces are occupied. 
The cube ordinarily is coated with an impermeable film 14 on its lateral 
faces. The purpose of this film is to reduce the surface of the substrate 
exposed to the ambient air in the final stages of the cultivation when the 
cubes are separated from one another (including when they are placed on 
the cultivation slabs as we will indicate below in connection with FIG. 
6). By reducing the exposure to the ambient air, the evaporation and the 
drying risks of the substrate and the necessity of joining the successive 
cubes when supplies of solution are limited. 
FIG. 2 shows, in perspective, a cube 20 according to the invention whose 
base 26 is not level but exhibits a concave cylindrical shape. As 
indicated above, this configuration exhibits the great advantage of making 
the cube rest only on two edges 22 and 24 of the base of the cube. The 
surface of contact then is extremely limited relative to the base surface. 
In practice, even if the material is quite rigid, there is, of course, a 
certain packing down of these edges. Nevertheless, from experience, the 
width of the strip of contact with the support ordinarily does not exceed 
3 to 5 mm on each side. For a cube with a total width on the order of 120 
mm, a contact area results which is much less than a tenth of the base 
surface. 
In the embodiment shown in FIG. 2, height h between the vertex of the 
cylindrical part of the base 26 and the lateral protuberances 22 and 24 is 
advantageously limited. On one hand, as we have indicated, a great height 
is not necessary to prevent the formation of a continuous liquid film at 
the base of the cube. For this purpose, several millimeters between the 
base of the cube and the support on which they rest is sufficient. On the 
other hand, it is preferable to limit this height so that, in a final 
phase of the cultivation, which is performed by placing the cubes on the 
cultivation slabs as shown in FIG. 6, the continuity of the contact of the 
substrate with the slabs is suitably assured. 
Actually, it is important, when the cube is in position on the slab, that 
the roots pass from one to the other without a great discontinuity between 
the cube and slab. If the distance separating the bottom of the cube from 
the upper surface of the slab becomes too great, the space thus formed 
will not promote the passage of the roots due to excessive aeration. In 
practice, since the cubes, like the slabs, consist of a semi-rigid 
material, applying a slight pressure on the cube, when the height h is not 
too great, practically makes it possible to bring the two surfaces into 
contact with one another. To be able to obtain this satisfactory 
installation, the height h is maintained preferably less than about 12 mm. 
If necessary, also to reduce the distance between the cube and the slab, it 
is possible to provide ribs on the surface of the slab in which the 
protuberances of the lower face of the cube are housed. 
The production of such cubes as shown in FIG. 2 can advantageously be 
performed from flat-face cubes which are shaped, for example, by a milling 
machine of corresponding shape. 
FIG. 3 shows a cube 30 exhibiting protuberances 34 in the shape of feet 
placed at the four corners of the lower face of the cube. This time, the 
lower face 32 is level. As above, the surface of contact with the support 
is significantly limited so that the drainage of the cubes can be 
performed rapidily. 
The protuberances 34, as above, advantageously consist of the same material 
as the substrate. The formation of these feet is obtained, for example, by 
cutting. The same above-mentioned considerations relative to height h are 
also applicable to the protuberances of this embodiment. 
In the two disclosed embodiments according to the invention, obtaining good 
drainage between each irrigation operation promotes a satisfactory 
development of the roots. In practice, the roots which preferably tend to 
reach the base of the cube are stopped in their progression by contact 
with the air. Lateral root branches then are created which promote a 
better use of the cube by a more complete colonization of the mass of the 
cube. 
The cubes, for reasons of convenience, ordinarily are marketed in rows 40 
formed of several assembled cubes, as shown in FIG. 4. The cubes are 
generally are joined to one another by lateral adhesive strips (not shown) 
which later can be either withdrawn or cut to separate the cubes. The 
adhesive strips, in this case, are applied to the impermeable film 14 
which surrounds the lateral faces of the cube. 
FIG. 5 shows, in section, a cultivation tank 50 of seedlings. Two 
successive stages of the cultivation are shown there. In the first stage, 
shown in the left part, rows of cubes 40 such as those shown in FIG. 4 are 
placed adjacent to the drain of the irrigation tank 54. In the second 
stage, shown at right, the cubes are disengaged and separated from one 
another. 
In this second stage of the cultivation, the subirrigation of the 
traditional cubes can lead to a movement of the cubes. Particularly if the 
ground is not perfectly horizontal, which is preferred to improve the 
drainage, the cubes can slide on a liquid film formed on the bottom 
surface of the cube. The absence of this film according to the invention 
rules out any risk of movement of the seedlings and therefore the 
obligation of manually reestablishing a momentarily compromised 
distribution. 
FIG. 6 shows the last stage of the cultivation. The cubes 20 are placed on 
larger slabs 60. Ordinarily, the slabs are also coated with an impermeable 
film 64 which limits the losses by evaporation. The impermeable film 64 is 
provided, on the upper part, with openings 62 corresponding to the 
locations of the cubes. 
As indicated above, it is important to assure a good contact between the 
cube and the slab. The latter was obtained automatically when the base of 
the cubes is perfectly level. This contact cannot be complete with the 
cubes exhibiting grooves. 
The use of the cubes according to the invention, either by applying a 
slight pressure when joining the cube and the slab, or by providing 
grooves on the slab, assures a satisfactory joining of the two cultivation 
substrates as long as, in the first case, the height conditions of the 
protuberances set above have been met. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.