CA1338795C - Mineral wool-based growing compounds - Google Patents

Abstract

The invention consists of mineral wool compounds used for soil-less cultivation.
The compound for soil-less cultivation as defined in this invention, is composed of mineral-fibre felt, processed in the form of blocks (10) suitable for the cultivation of a multiplicity of seedlings. The main feature of this compound is that the structure of the blocks is such that, when in use, the fibres are arranged essentially in the vertical plane (9).
As defined in this invention, the compound brings about an improvement in the performance of seedlings.

Description

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 1 - ~L
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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 '!, X
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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 ~'X

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-1 33~795 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 X~
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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 1 X.
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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 X
~ . ~;, 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 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 ', X

, 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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, -t 338795 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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Claims (6)

1) A plant growing compound comprising a block having upper and a lower surface and side surfaces, the block consisting of mineral wool fibres, said fibres extending from the lower surface to the upper surface of the block, so that when the block is in the plant growing position on a support, the fibres are vertically orientated with respect to the support.

2) The growing compound of Claim 1 including a sheath means wrapped around the compound.

3) The growing compound of Claim 2 wherein the sheath means is a plastic sheath.

4) The growing compound of Claim 3 wherein the sheath is in the form of a sleeve rendered a close fit to one or more of the outer surfaces of the growing compound.

5) The growing compound of Claim 1 in multiplicty with fibres orientated in similar manner with the close fit sleeve of Claim 4.

6) The growing compounds of Claim 5 in multiplicity with fibres orientated in dissimilar manner within the close fit sleeve of Claim 4.