This invention relates to a seed germination medium for encouraging the germination and establishment of seeds.

Background of the Invention The use of seed mats or seed strips for planting and germinating seeds has been in use in agriculture and horticulture for a number of years. Such seed mats or seed strips typically comprise a cover layer and a base layer between which seeds are held. It has also been proposed to include in the seed mats and seed strips various substances that assist seed germination and plant growth. U.S. Pat. No. 5,189,833 discloses an arrangement in which lawn grass seeds are germinated in a thin layer of growing medium sprayed over a mat of non-woven polypropylene lying on top of an impermeable membrane. After a few days of germination, the mat carrying the seed-bearing medium can be lifted, rolled and then spread over an appropriately conditioned and prepared lawn bed. Australian Patent Application AU-A-81394/75 discloses a seed bearing mat comprising upper and lower layers bonded together with a latex adhesive, seeds being bonded between the layers. The lower layer is a water permeable material such as straw, coconut fibres, peat moss or wood shavings whilst the upper or covering layer is formed from materials of a finer texture than the lower layer such as coconut fibre dust or sawdust bonded together by latex. The seed bearing mat of AU-A-81394/75 is described as being particularly useful in preparing lawns.

French Patent Application FR-A-2505607 discloses a non-laminar seed germination medium comprising a folded layer of a transparent plastics material such as

polyethylene having bonded to the edges of the underside thereof a water-soluble or degradable seed-bearing medium such as paper. In use, the seeds germinate beneath the transparent plastics layer and, as the seedlings grow, they lift the transparent layer away from the water-soluble/degradable medium. Thus the transparent layer is gradually unfolded and carried upwards by the growing seedlings and therefore remains in place over the top of the plants to maintain a greenhouse effect. French Patent Application FR-A-2440438 discloses a peat-based seed bearing medium comprising a lower layer formed of a water-permeable fibrous material such as cellulose fibres or muslin cloth, an intermediate layer of peat containing seeds and any additives; and optionally an upper layer which is also water-permeable and can be formed from a material such as muslin.

International Patent Application WO-A-96/28010 discloses a seed germination medium in sheet form having upper and lower layers and seeds disposed therebetween. The upper and lower layers are preferably formed from a biodegradable paper material. In order to assist anchoring of the medium in the underlying soil or, in the case of desert areas, sand, the medium is slit longitudinally to enable it to be stretched laterally to form an open lattice.

WO-A-99/22580 (Eurostar Biologicals) discloses a seed-germination medium

comprising an upper layer formed from a biodegradable material which is permeable to gases but substantially impermeable to water in liquid form; a lower layer formed from a water-absorbent biodegradable material; seeds being disposed beneath the upper layer; and the upper layer having a plurality of perforations therein to enable seedlings germinating from the seeds to grow therethrough. WO-A-00/67549 (Terraseed) discloses a seed-germination medium comprising an upper layer formed from a tissue paper having a weight of approximately 10-30 g/m2, the tissue paper being coated or impregnated with a waterproofing agent such that the tissue paper is permeable to gases but substantially impermeable to water in liquid form; a lower layer formed from a water-absorbent biodegradable material; seeds being disposed beneath the upper layer; and the upper layer optionally having a plurality of perforations therein to assist disruption of the upper layer to enable seedlings germinating from the seeds to grow therethrough.

WO-A-2005/099431 discloses a crop production apparatus including an upper layer comprising a flexible sheet of non-degradable or biodegradable material and a seed impregnated or carrying lower layer formed from water-absorbent biodegradable material bonded or otherwise attached to the upper layer and removable therefrom.

A seed germination medium of the type described in WO-A-00/67549 is currently in commercial use. The medium is provided in the form of a roll which is carried on a vehicle and can be gradually fed out from the roll as the vehicle moves across a field or other agricultural site. In order to hold the medium in place, for example to prevent it from being displaced in windy conditions, a layer of sand is deposited over the top of the medium as it is unrolled. Whilst effective, the need to carry a supply of sand on the vehicle not only represents a further expense, but sourcing the right type of sand in large enough quantities can prove problematic. In addition, the need to replenish the laying vehicle's sand supply at regular intervals slows down the laying process.

The Invention

The present invention provides a solution to the problems inherent in the known commercial seed mats described above. Thus, according to the invention, one or both sides of a seed germination medium is coated, either in situ or during the manufacturing process, with a water absorbing substance that acts as an adhesive to stick the germination medium to the underlying substrate (e.g. soil). By coating both the upper and lower surfaces of the seed germination medium, not only can the seed germination medium adhere to the underlying substrate but a thin layer of soil can be placed over the seed germination medium and will stick to the medium and further help to retain it in place.

Accordingly, in a first aspect, the invention provides a seed germination medium comprising a cover layer and a base layer and a plurality of seeds disposed

therebetween, the cover layer and base layer both being formed from a biodegradable material; the cover layer being permeable to water, and the base layer being formed so as to allow roots of germinated seeds to grow downwards through the base layer;

wherein the cover layer has on an upper surface thereof a coating of a water-absorbing substance. In a second aspect, the invention provides a seed germination medium comprising a cover layer and a base layer and a plurality of seeds disposed therebetween, the cover layer and base layer both being formed from a biodegradable material; the cover layer being permeable to water, and the base layer being formed so as to allow roots of germinated seeds to grow downwards through the base layer; wherein the base layer has on a lower surface thereof a coating of a water-absorbing substance.

The seed germination media of the invention are of a laminar construction, and the cover layer and base layer typically comprise layers bonded together in such a manner that they cannot readily be separated without destroying them. In this respect, the media are distinguished from the media disclosed in FR-A-2505607 which are of a non-laminar arrangement in which the upper and lower sheets are connected only at their respective edges such that the upper sheet can be lifted away from the lower sheet by the action of the growing plant. The base layer can be made from a wide range of bio-degradable materials including cellulosic materials such as papers, and in particular papers such as air-laid paper (e.g. an air-laid latex bonded paper, such as a paper formed from fluff pulp and a latex binder); waste or recycled paper; Kraft paper or other fibre-based or waste products. The selection of a suitable material for the lower layer will be dependent on the cost, availability of raw materials, the soil type, irrigation method, degree of capillarity required and the amount of water which must be retained in the medium to facilitate

establishment of the seedling.

In one embodiment, the base layer is formed from a paper. The paper can be either a wet-laid paper (e.g. a Kraft paper) or an air-laid paper.

An advantage of an air-laid paper is that the loose network of fibres making up the paper allows roots to grow through into to the underlying soil. The air-laid paper may have a base weight of 40 and 80 gsm, a thickness of between 1 and 2 mm, and a tensile dry strength typically between 400 and 1500 cN/5cm (Edana test). The air-laid paper is typically manufactured using vinyl acetate/ethylene copolymer (VAE) and/or starch based binders.

Instead of air-laid paper, a wide range of conventional tissue, Kraft, lining and newsprint papers can be used for the base layer instead provided that they do not contain phytotoxic or environmentally harmful substances. Preferably therefore, the papers are made from virgin pulp, or from recycled materials of known provenance where the risk from printing inks etc, can be eliminated (e.g. trimmings from cardboard manufacture). The papers can have, for example, a base weight of 30 to 100 gsm, a thickness of 0.3 to 1 mm, and a tensile dry strength 500 and 2000 cN/5cm. They are typically

manufactured with petroleum-based (e.g. VAE) or starch based binders. Wet-laid papers such as Kraft papers (i.e. paper made by the kraft process) are advantageous in that they are widely available and are significantly less expensive. Although the tighter fibre network typically found in a wet-laid paper can mean that the roots of germinating seedlings are less able to penetrate the paper, this can be compensated for by perforating the paper (e.g. by needling or cutting with blades) in order to create openings through which the roots of seedlings can grow.

The cover layer may also be formed from a cellulosic material such as paper. The cover layer is constructed such that germinating seeds can grow through the layer. Therefore, either a relatively lightweight or loose-textured paper can be used, or a heavier more dense paper can be used but with perforations to allow penetration by seedlings.

In one embodiment, the cover layer is formed from a tissue paper.

The term "tissue paper" paper as used herein refers to a lightweight material with relatively poor mechanical strength typically having a weight of approximately 10 to 30 g/m ² , more usually 15 to 25 g/m ² , for example from 17 g/m ² to 24 g/m ² . The tissue paper typically has sufficient mechanical strength to enable it to remain intact during manufacture and laying but is preferably sufficiently weak when wet to allow stronger seedlings to grow through. For stronger grades of tissue paper, for example papers at the upper ends of the weight ranges set out above, perforations may be present in the upper layer to assist the growth of seedlings, particularly where the seedlings are of insufficient strength to burst or "punch" though the tissue.

The tissue paper can be calendered to give a polished surface and an example of such a calendered paper is sulphite paper available from Kruger Tissue, Church Stretton, Shropshire, UK.

The base layer can be a single layer or it can comprise a plurality (e.g. two, three or four) of layers. As with the cover layer, the base layer is preferably perforated to ensure the penetration of roots emerging from the seeds. The base layer can advantageously be coloured or treated to manipulate climatic conditions (e.g. to absorb or reflect heat) and to suppress weed growth below the medium. For example, the medium, or at least the surfaces thereof, can be provided in a variety of colours to assist soil

warming/cooling or to exclude light so as to suppress weed growth and aid plant establishment. The medium may have different colours on its upper and lower surfaces to enhance or reduce the absorption of radiation on one surface and produce the opposite effect on its other surface.

The seed germination medium of the invention has on either or both of its upper and lower surfaces thereof a coating of a water-absorbing substance. The water absorbing substance, when wet, forms an adhesive layer that serves to stick the germination medium to an underlying substrate such as soil thereby avoiding or reducing the need for the application of sand to the upper surface during laying to prevent displacement by wind or other factors. If a layer of sand is placed over the seed germination medium after laying, the presence of a wet adhesive layer of water-absorbent substance on the upper layer means that sand will stick to the adhesive layer and consequently less sand will be required in order to weigh the medium down and hold it in place. The water- absorbing substance, whether on the upper or lower surface, also serves to keep the seed germination medium moist and prevent it from drying out.

The water-absorbing substance may be one which swells to form a gel or expands to form a foam on contact with water.

The water-absorbing substances can be synthetic or natural materials (such as clay minerals, e.g. bentonite clays), gelatine products, starch-based products, natural gums such as galactomannan gums (e.g. guar gum and locust bean gum) and xanthan gum, polymeric gels such as polyoxyethylene gels (PEO), silica gels, psyllium husk and socalled "super absorbents" such as super absorbent acrylic polymers (e.g.

polyacrylamide), which may be added to the medium at between 5 and 100 gsm, preferably 10 to 40 gsm, for example up to about 30 gsm depending on use.

Polyacrylamide is available for agricultural use from a range of suppliers including, for example, Glowcroft Ltd. Polyoxyethylene gels can be obtained from SmartTech Limited of Glasgow, UK, a particular PEO gel being cross-linked polyethylene oxide co- polyurethane hydrogel.

The water-absorbing substance is one which, when wet, has adhesive properties. As such, it is distinguished from substances such as sand, which, although capable of absorbing water, do not function as adhesives and cannot stick the seed germination medium to components of an underlying substrate or materials deposited onto the upper surface of the medium.

In one embodiment, the water-absorbing substance on the upper surface of the cover layer can comprise starch, a starch-derived material or a superabsorbent synthetic polymer such as polyacrylamide. The coating of the water-absorbing substance may include other optional additive materials as described below. In addition, the coatings may contain one or more substances that can assist gel or foam formation, or can liberate gases to form a foam, or can release, or react with other substances in the coatings or in the underlying (or overlying) substrate to form, oxygen and thereby oxygenate the soil. An example of an oxygen-forming substance is sodium percarbonate.

The base layer of the seed germination medium of the invention may have a coating of a water-absorbing substance on a lower surface thereof. The water-absorbing substances that may be applied to the lower surface of the base layer may be the same as (or different from) the water-absorbing substances applied to the upper surface of the cover layer.

Thus, for example, the water-absorbing substance on the lower surface of the base layer may comprise starch, a starch-derived material or a superabsorbent synthetic polymer such as polyacrylamide.

In one embodiment, the water absorbing substances on the cover layer and the base layer are the same.

The water absorbing substance(s), upon hydration, typically form an adhesive layer which is capable of sticking to substrate particles such as soil and sand particles. The water absorbing substance(s), upon hydration, may form an adhesive gel or foam which is capable of sticking to substrate particles such as soil and sand particles.

The cover and base layers are typically bonded together by means of an adhesive. The adhesive is typically one which is non-phytotoxic, and most preferably is water-based. Examples of such adhesives are starch, starch derivatives, polyvinyl alcohol (PVA) and ethylene vinyl acetate (EVA), collagen glues, dextrin and starch-based glues, polylactic acid (PLA) biopolymer adhesives and hot melt glues, each optionally in combination with other adhesives.

Seeds are held between the cover layer and base layer. The seeds are present in an arrangement and a density that reflects the nature of the crop to be produced from the seeds. Where the base layer is perforated to allow the roots of seedlings to grow through the base layer, the seeds may be deposited so that they are in register with the perforations, e.g. they lie over the perforations. The dimensions of the perforations are therefore selected such that seeds cannot fall through them. In a similar manner, if the upper layer is perforated, the arrangement of the seeds may be such that they are in register with (e.g. lie beneath) the perforations.

In addition to the seeds, a range of optional additive materials can be disposed beneath the cover layer.

For example, fertilizers, micro-nutrients (such as zinc, copper, boron, and seaweed extracts), iron (III) phosphate, soil improving agents, biological agents such as beneficial soil bacteria and mycorrhizal fungi, humic acid, sea kelp, sugars, amino acids, plant growth promoters and hormones such as gibberellins and auxins, pH-regulators such as lime and sulphur, salt binding agents such as gypsum (calcium sulphate) and adsorbents such as activated carbon can be incorporated into the medium either by formulating with the adhesive or by application directly to one or other of the internal surfaces as a spray, granule or dust. The pH-controlling agents can be used to control the acidity of the immediate environment, and agents such as gypsum and activated charcoal can minimise the impact of adverse chemical contaminants and salt in the soil or medium, as well as to improve germination, and/or to aid and accelerate plant establishment. Salt binding compounds, buffering and pH regulating compounds and adsorbents typically are applied at between about 20 gsm and 200 gsm, more usually 50 to 150 gsm, for example approximately 100 gsm. In the case of the adsorbent, activated carbon, lower concentrations are typically used.

A range of microbiological additives can be incorporated into the seed germination media of the invention to assist germination and plant establishment. These are typically mycorrhizal fungi. Mycorrhizae are a group of about 400 fungi that form symbiotic relationships with plants. They live in or on the roots, extend their hyphae into the soil and make phosphate, nitrogen other nutrients and water available to the host plant. They extend the effective root area many hundreds of times so plants grow faster, larger and stronger with less fertiliser and water. Other commercially available biological and chemical agents that stimulate plant defences and encourage beneficial symbiotic mycorrhizal associations may also be included.

The buffering and other chemical organic agents provide a means of counteracting the impact of adverse chemical contaminants in the soil or medium, as well as improving germination, and/or aiding and accelerating plant establishment. Thus, for example, lime provides a buffer against low pH, gypsum provides a means of counteracting high salinity, whereas clay minerals such as zeolite, kaolinite, calcium bentonite and montmorillonite counteract high levels of fertiliser or chemical contamination in the soil.

Fertiliser and micronutrients may be added to the medium either by incorporation with the adhesive or applied directly to one or other of the internal surfaces as a spray, granule or dust. If applied at high levels, fertilisers will produce a high level of EC (electro-conductivity) in the medium, which will scorch and kill emerging seedlings. Consequently the rate of application, the type of fertiliser used and the rate of release generally require careful control. Typically, organic based fertilisers are used since such fertilisers release nitrogen more slowly allowing higher rates to be included in the medium without risk of damage to seedlings. A typical application would be of a granular, organic-based material at between 10 and 100 grammes per square meter (gsm), more typically 30-80 gsm. Fertilisers can vary considerably in their potassium, phosphorus and nitrogen contents, but one fertiliser useful in the media of the invention contains 16% nitrogen, 10% phosphorous and 10% potassium plus micro-nutrients. The optional additive materials can be present between the cover and base layers but instead, or in addition, they may be present in the coating of water absorbent substance on the base layer and/or the cover layer.

The nature of the adhesive used to bond the cover layer to the base layer may be selected so as to give a desired rate of release of the optional additive materials. Thus, the adhesive used to bind the cover layer to the base layer can also be used to slow down the release of additives (fertilizer, pesticide, mycorrhiza etc.). A rapid release of additives can be phytotoxic to young seedlings and a delayed release can be beneficial and allow a higher loading than could be applied as a seed dressing.

Additives can also be placed at some distance from the seed, further increasing this advantage. Tests carried out looking at the rate of release of dye in combinations with PVOH and Acrylic adhesives have shown immediate release with 100% PVOH, with no immediate release with acrylic binders. After 10 days 100% release from the acrylic adhesive was achieved with a graduated response with mixtures of the two adhesives

Alternatively, or additionally, any one or more of the optional additive materials may be encased in a release-controlling coating so as to obtain a desired rate of release of the materials. Such release controlling coatings are well known and can comprise natural or synthetic polymers. Any such polymers must be compatible with the plants to be grown from the seeds and should ideally be non-phytotoxic.

The combination of cover and base layers with the seed and optionally other materials disposed therebetween (the "uncoated seed germination medium") can be prepared by the general methods described in our earlier International patent application

WO00/67549. Thus, a process for manufacturing the uncoated seed germination medium can comprise:

(i) providing a first web formed from a material which will constitute the base layer; (ii) optionally forming a plurality of perforations in the first web;

(iii) depositing seeds onto the first web; (iv) providing a second web formed from a material which will constitute the cover layer,

(v) optionally forming a plurality of perforations in the second web, where such perforations are not already present;

(vi) optionally depositing adhesive on one or both of the first and second webs; and

(vi) bonding the first and second webs together.

The uncoated seed germination medium can then be coated with the water absorbing substance on the lower surface of the base layer and/or the upper surface of the cover layer in a separate step or steps. In one embodiment, the uncoated seed germination medium is coated with the water absorbing substance in liquid form at the point of use of the medium. In this

embodiment, a slurry, paste, gel or other aqueous liquid form of the water absorbing substance can be coated onto the uncoated seed germination medium while the seed germination medium is being deposited onto a substrate. In another aspect, the invention provides a method of depositing seeds or a bioactive substance onto an agricultural or horticultural substrate; which method comprises laying over the substrate a biodegradable membrane containing the seeds or bioactive substance; wherein at least a lower surface of the membrane has coated thereon a substrate-adherent substance that adheres the membrane to the substrate. The substrate-adherent substance may be a water-absorbing substance of the type defined herein, and references to "substrate-adherent substance" may be taken to include any one or more of the water-absorbing substances defied herein.

The substrate-adherent substance may be a biodegradable substance. The term "biodegradable substance" as used herein refers to a substance that degrades under the influence of environmental conditions. Thus, it may be degraded biologically by bacteria, fungi, microfauna, or may be degraded chemically, for example by hydrolysis, oxidation or photodegradation; or may be degraded mechanically by shearing or frictional forces applied to or within the soil.

At least a lower surface of the membrane has coated thereon a substrate-adherent substance that adheres the membrane to the substrate. More usually, however, an upper surface of the membrane also has coated thereon a biodegradable substance which is capable of sticking to substrate particles such as soil and sand particles.

The substrate-adherent substance may be coated onto the membrane in the form of a slurry, paste, gel or other aqueous liquid form of the water absorbing substance and can, for example, be coated onto the uncoated seed germination medium while the seed germination medium is being deposited onto a substrate.

The substrate-adherent substance may be applied to the membrane immediately before the membrane is laid over the substrate.

The substrate-adherent substance may be applied to the membrane in a variety of different ways but typically it is applied to the membrane by spraying or extrusion or by means of a roller applicator.

In one embodiment, the substrate-adherent substance is coated onto the membrane in the form of a foam or gel. One or more foaming or gelling agents may therefore be included in compositions of the substrate-adherent substance to be applied to the substrate. The foaming agents can be, for example, biocompatible surfactants.

Compressed gases such as compressed air may be passed through the coating composition to form a foam before application to the membrane. Alternatively, carbon dioxide may be generated in situ by the inclusion of effervescent couples comprising an acid and a bicarbonate salt or carbonate salt, for example in the form of ground chalk. Oxygenating agents may also be included in the coating compositions. In one embodiment, the coating composition comprises an inorganic peroxide such as sodium percarbonate as an oxygenating agent.

The membranes used in the method of the invention may have a laminar structure and comprise a cover layer and a base layer as defined above. Thus, the membrane may be an uncoated seed germination medium as hereinbefore defined.

The membrane contains seeds and may also include any one of more of the optional additive materials as hereinbefore defined.

In one embodiment, the membrane contains one or more bioactive substances selected from pest control agents, weed control agents and growth promoting substances (such as auxins and gibberellins). The agricultural or horticultural substrate onto which the membrane is laid is typically selected from soil and sand and mixtures thereof.

The membrane may be laid onto the substrate by uncoiling from a roll and the substrate-adherent substance coated onto the membrane as it is uncoiled from the roll. For example, the substrate-adherent substance may be sprayed, applied or extruded onto the membrane as the membrane is uncoiled from the roll.

In a further aspect, the invention provides a method of depositing seeds or a bioactive substance onto an agricultural or horticultural substrate; which method comprises coating one or both of the upper and lower surfaces of a biodegradable membrane with a substrate-adherent substance as hereinbefore defined, wherein the seeds and/or bioactive substance and any optional additive materials as hereinbefore defined are contained in, or held against the membrane by, the substrate-adherent substance; and then laying the coated membrane onto the substrate.

In one variant of this process, seeds and/or the bioactive substances are deposited onto an upper surface of the membrane before the coating of substrate-adherent substance is applied to the membrane.

In another variant of the process, seeds and/or the bioactive substances are

incorporated into the substrate-adherent substance before it is applied to the

membrane. In a further variant, a mixture of the substrate-adherent substance and loose-fill fibre materials (typically fibres from natural products) and the seeds and/or bioactive substances is coated onto the upper or lower surface of the membrane before laying the membrane onto the substrate. In one embodiment, the mixture is applied to the upper surface only and a coating of substrate-adherent substance containing no seed or bioactive substance is applied to the lower surface. In another embodiment, the mixture is applied to the lower surface only and a coating of substrate-adherent substance containing no seed or bioactive substance is applied to the upper surface. In a further embodiment, the mixture is applied to both upper and lower surfaces.

In another variant of the above process, the substrate-adherent substance and loose-fill fibre materials are applied to an upper surface of the membrane, seeds are then deposited onto the coated membrane, optionally an overcoating of the substrate- adherent substance is applied to cover up the seeds and/or bioactive substance, and the membrane is then laid onto the agricultural or horticultural substrate.

In each of the foregoing aspects and embodiments of the invention, the membrane can be formed from a cellulosic material such as a paper as hereinbefore defined. The paper may be an air-laid or wet-laid (e.g. Kraft paper) as hereinbefore defined and may be perforated to assist root and plant growth from the germinating seeds.

The membrane may be supplied and used in a pre-perforated condition, or perforations may be created by appropriate machinery in situ during the laying process.

Brief Description of the Drawings Figure 1 is a schematic illustration of an embodiment of the invention in which a coated seed germination medium has been coated in situ before laying onto a soil substrate.

Figure 2 is a view of the region marked A in Figure 1 but with the inter-row plants omitted for clarity.

Figure 3a is a plan view of a length of uncoated seed germination membrane formed from one combination of paper layers.

Figure 3b is a plan view of a length of uncoated seed germination membrane formed from an alternative combination of paper layers.

Figure 3c is a schematic sectional view of the membrane of Figure 3a but with one seed shown as having germinated. Figure 3d is a schematic sectional view of the membrane of Figure 3b but with one seed shown as having germinated.

Detailed Description of the Invention

The invention will now be illustrated but not limited by reference to the accompanying drawings 1 , 2, and 3a to 3d. Figures 1 and 2 show a seed-containing membrane (seed germination medium) 2 after laying in a shallow trench 4 in the ground. The seed containing membrane contains seeds 8 and is covered by a layer 6 of a gel formed from a water absorbent substance. The gel comprises a cross-linked polyacrylate and may optionally include natural fibres and various additive materials such as plant growth promoters, soil improvers, trace elements and fertilisers. The underside of the membrane is also coated with the polyacrylate gel.

The structure of the seed-containing membrane is shown in more detail in Figures 3a to 3d.

In one embodiment, as shown in Figures 3a and 3c, the membrane comprises a cover layer 10 formed from a tissue paper. The tissue paper is formed from recycled or virgin pulp with no binder and is typically a single ply tissue having no wet strength.

A base layer 12 of an air-laid paper is bonded to the cover layer 10 by means of an ethylene vinyl acetate emulsion adhesive, an example of which is the E3383-C

Emulsion Adhesive available from Terraseed Limited, of Kingsclere Road, Tadley, Hants, UK. The base layer 12 and cover layer 10 together form a laminar structure which contains an array of seeds 14 sandwiched between the layers.

Because the air-laid paper from which the base layer 12 is formed has a fairly open structure, the seed radicles of germinating seeds can grow through the paper as shown in Figure 3c. There is no need to perforate the base layer. The germinating seed can also grow up through the cover layer of tissue without the need for perforations in the cover layer.

An alternative combination of paper types is used in the membrane shown in Figures 3b and 3d.

In the embodiment shown in Figures 3b and 3d, the membrane comprises a cover layer 10 formed from a tissue paper of the type described above for the embodiment of Figures 3a and 3c.

However, the base layer 16 is formed from a wet-laid paper such as a Kraft paper. The layer 16 of wet-laid paper is bonded to the cover layer 10 by means of an ethylene vinyl acetate adhesive as described above. The base layer 16 and cover layer 10 together form a laminar structure which contains an array of seeds 14 sandwiched between the layers.

Because the wet-laid paper from which the base layer 16 is formed has a more dense structure, the seed radicles of germinating seeds cannot readily grow through the paper as they can with the paper shown in Figure 3a and 3c. Therefore, the base layer 16 is provided with an array of cuts or slits 18 through which the seed radicles can grow as shown in Figure 3d.

The membranes shown Figures 3a to 3d are manufactured by a process analogous to that described in WO00/67549 but omitting the water-proofing coating on the upper surface of the cover layer. The membrane thus formed is stored in the form of a roll and transported to the location where it is to be used. It can then be rolled out from a moving vehicle and deposited in the shallow trench 4. Before it is deposited into the trench, it passes over a roller applicator where a layer of an aqueous slurry of a gel-forming polyacrylate is applied to the under-surface of the membrane. At approximately the same time, a mixture of the same gel-forming substance together with a loose fill natural fibre material is applied to the upper surface. Once the coated membrane has been deposited in the shallow trench, the gel coating on the lower surface of the membrane adheres the membrane in place on the underlying soil and the weight of the fibre- containing gel coating on the upper surface further helps to anchor the membrane in place. In addition to helping prevent the membrane from being dislodged, for example by wind, the gel substances provide a source of moisture for the germinating plant and help prevent the membrane from drying out.

A further advantage of the gel coatings is that they can be used as carriers for a wide variety of substances that assist plant growth as described above. It will readily be apparent that numerous alternations and modifications could be made to the medium shown in the accompanying drawings and described in the Examples without departing from the principles underlying the invention and all such modifications and alterations are intended to be within the scope of this application.