The invention also relates to a method for preparing a ground cover of this type, to a dry pulverulent mixture for producing a ground cover of this type and to a method for preparing a biologically degradable ground cover suspension.

A biologically degradable ground cover of the type described in the preamble is known from WO 00/32030. The binder mentioned in this publication is, for example, a latex, such as a natural or synthetic latex or styrene. The ground cover is formed by simultaneously and separately applying 1) an aqueous solution which comprises a binder which solidifies in air, such as a latex, as well as if appropriate fillers and other active substances, 2) a mixture of dry natural fibres optionally mixed with an opacifier to the ground which is to be covered.

Drying of the binder causes the natural fibres to adhere to one another so as to form a cohesive ground cover. One drawback of this way of forming a ground cover in situ is the fact that binding of the fibres is only obtained by drying of the latex.

Therefore, it is not recommended that a ground cover of this type be applied during humid or wet weather. A further drawback is the complexity of applying a mixture comprising dry fibres to the ground. This application step requires specific devices which have to be set accurately and, for example if the moisture content of the fibres is not optimum, make it difficult to achieve homogeneity of the fibre coverage over the ground.

The invention provides an improved biologically degradable ground cover of the type described in the preamble which can be formed in situ on the ground under virtually all weather

conditions without complex devices having to be used, and is characterized in that the organic binder comprises alginate and the biologically degradable fibres are held in a liquid medium.

In this context, the term liquid medium is to be understood as meaning any medium in which the biologically degradable fibres can be well distributed. This liquid medium is expediently water. The solvent for the alginate to be used is also expediently water.

Alginate has binding properties in an aqueous suspension, which means that there is little or no likelihood of it being washed out of the ground cover, which can therefore also be applied to the ground in the form of a suspension.

The term"ground"is to be understood as meaning the type of land which is suitable, for example, for agricultural purposes. The term"biologically degradable" (or biodegradable) is to be understood as meaning that the material in question loses its strength and cohesive nature and can ultimately disintegrate under the action of micro-organisms and/or the influence of weather over the course of time, with the result that the nonwoven which is formed disappears and can easily be worked into the ground. The time which is required for this pattern is preferably less than one year, more preferably less than six months and most preferably less than three months. If suitable fibres are selected, it is even possible for the disintegrated nonwoven material to serve as a food source for plant growth. It is also possible for the nonwoven material to be worked into the ground while it is still intact after use, in which case it can serve as a food source. For this purpose, the material may contain, for example, additional fertilizers. The advantage of a biologically degradable ground cover according to the invention also resides in the fact. that it can be sprayed onto the land, in which the desired plants are already growing, in the form of a liquid medium, preferably an aqueous medium, such as an aqueous suspension. After it has been applied, a continuous nonwoven will form, with the result that the growth of weeds and undesired plants is counteracted in this way. A biologically

degradable ground cover of this type represents an excellent alternative to the plastic sheets which have hitherto customarily been used and are laid in strips over areas of agricultural ground.

The alginate in the ground cover is expediently crosslinked with a crosslinking agent which comprises divalent cations. It is known that alginate can be crosslinked with divalent cations; crosslinking of this nature leads to the formation of a strong structure which can have a sufficient resistance to mechanical loading. The ground cover may even be sufficiently strong to be able to support a person without being damaged.

The crosslinking agent preferably comprises Ca2+ ions. Of divalent ions, it has been found that calcium is the most suitable and allows optimum crosslinking of the alginate.

In connection with the invention, reference is also made to the following literature: US-A 6,029, 395 has disclosed a biologically degradable ground- cover material which is formed by an open-cell foam material and which has to be foamed first of all before the ready-to-use mats are placed onto the ground. There is no mention of a material which can be formed in situ.

EP-A 0 578 107 describes nonwoven materials which are needled in order to be stabilized. At least on the outer side, the nonwoven materials are covered with a layer of biologically degradable material, such as starch or alginate. This publication does not describe a ground-cover material which can be formed in situ.

GB-B 641 280 describes a material, such as a flowerpot or plate- like seed or plant carrier which consists of natural moisture- absorbent fibre material, such as turf, moss or the like, which is mixed with an alginate as binder and if appropriate is coated with a calcium salt solution in order to improve the cohesion.

This publication likewise does not describe a ground-cover material which can be formed in situ.

In the context of the present invention, the term biologically degradable fibres, as has already been explained above, is to be understood as meaning fibres which lose their strength and cohesive nature as a result of the action of micro-organisms and/or the influences of weather over the course of time. The fibres are preferably of vegetable and/or animal origin.

The term"fibres of vegetable and/or animal origin"is to be understood as meaning all fibres which can be obtained and/or produced from animal or vegetable material. Examples of suitable fibres include coir fibres, sisal fibres, wheat straw, rice straw, corn fibres, kapok, flax, linen, cotton, hemp, jute, ramie fibres, wood fibres, paper fibres, cellulose fibres, manure fibres, animal fibres, such as wool, pet and livestock hair, collagen fibres, etc. The fibres are preferably selected from the group consisting of wood fibres, paper fibres, cellulose fibres, manure fibres, fibres of plants or a combination of two or more of these types of fibres. Fibres of this type are inexpensive, impart sufficient strength to the cover and form fertilizers for the ground after the ground-cover material has degraded.

The length of the fibres is preferably between 50-1000 pm. Since the ground cover is preferably applied in the form of a liquid medium, in particular an aqueous medium, it is important that a medium of this type can be pumped successfully without there being any risk of the pump installation becoming blocked. Fibres which are longer than 1000 um require powerful, heavy and expensive pump installations which are difficult to handle out in the fields. It has been found that the pump ability of the medium is good if it has a fibre length of between 50 and 1000 um, even in simple spray installations which are used, for example, to spray crops with agricultural pesticides, herbicides, fungicides and the like. For this purpose, the length of the fibres is preferably between 100-700 um, more preferably between 100-500 um, and most preferably between 100-300 um.

In an attractive embodiment of the invention, the ground cover comprises a light-retarding agent. The term"light-retarding agent"is to be understood as meaning when the agent is included in the ground cover, less light is transmitted through the cover to the ground. Preventing the transmission of light counteracts undesired growth of, for example, weeds and other undesired plants. Examples of light-retarding agents include dyes and pigments, which allow different wavelengths of light to be selectively transmitted or blocked. Examples include carbon, which produces a black colour. If sufficient carbon is included, it is possible to obtain total light absorption. The person skilled in the art will be able to select an appropriate quantity of carbon for the desired effect. Suitable carbon sources are known to the person skilled in the art, such as Norit AA, CN3, SA2 (Norit, The Netherlands). Other suitable dyes and pigments are known to the person skilled in the art; examples include tartrazine (yellow), erythrosine (red), indigotin (blue), chlorophyllin (green). It is also possible to use combinations of pigments or dyes.

The ground cover may also contain dyes in order to impart a suitable ground colour to the cover material, so that the material is not adversely perceived in the landscape. It is also possible, however, to opt for one or more striking colours, in order to be able to distinguish, for example, between separate parcels of land.

The ground cover according to the invention is water-permeable, so that the ground receives sufficient moisture, and may, depending on the incorporation of a light-retarding agent and its concentration, have a desired retarding and/or selective action with regard to the transmission of light.

The air permeability of the ground cover material can also be controlled as a function of the choice of fibres. If large fibres are selected, the air permeability over the course of time will be greater than for a cover material made up of shorter fibres. However, to obtain the correct consistency of

the cover material, it is also possible to opt for a mixture of fibres of different sizes.

It has been found that even a thin nonwoven with a thickness of 0.5 mm can produce a strong ground cover. A layer thickness of this nature has proven to be sufficiently able to withstand external mechanical influences (such as for example hail or torrential rain) and can also be walked on successfully.

Although thicker nonwovens are also possible, they are less attractive for cost reasons.

In connection with the invention as described above, it should also be pointed out that it is important for the ground-cover layer which is formed in situ on the ground to retain its cohesion during the period in which biological degradation of the binder and/or the fibres has not yet occurred to a significant extent. As long as the ground cover still contains some water, it is very stable. However, if periods of high temperature and/or low atmospheric humidity occur, the water content may drop below a desirable value, such as for example to below at least 10%, based on the weight of the dry matter of the material, which can lead to loss of cohesion.

One solution may involve regular moistening of the ground cover in order to keep its moisture content above 10% by weight.

A better solution is to incorporate a plasticizer in the material in order to prevent it from losing its cohesion. The plasticizer primarily influences the binding properties of the optionally crosslinked alginate binder.

Suitable plasticizers can be selected from a wide range which will be immediately obvious to the person skilled in the art. Examples of suitable plasticizers include organic polyols, such as ethylene glycol, propylene glycol, glycerol, polyethylene glycol and the like. Among these materials, glycerol has given good results. The invention also relates to a method for applying a biologically degradable ground cover to the surface of an area of ground, comprising the steps of:

a) preparing at least a first and second liquid medium, the first medium comprising biologically degradable fibres and the second medium comprising alginate, b) applying the media prepared in step a) to the ground.

As has already been indicated above, media of this type, which are preferably aqueous media, can be used to form an excellent biologically degradable ground cover of sufficient strength and durability which, moreover, has the desired air-and water- permeable properties. The media can be prepared in a way which is known in the specialist field and can be applied to the area of ground which is to be covered in a known way, such as for example by spraying, atomizing, etc.

The first medium and the second medium are preferably combined during the preparation step. They can be combined by the first medium and second medium being prepared separately and then brought together, but it is preferable to prepare a combined first and second medium by introducing the biologically degradable fibres and the alginate into a common liquid medium.

The first medium and the second medium, as well as the common medium, are preferably aqueous media. Combining the first medium and the second medium allows them to be applied to the ground which is to be covered in a single step, for example by spraying, atomizing, etc. However, it is also possible for the first medium and the second medium to be applied to the ground separately, in which case it is preferable for the first medium to be applied prior to or at the same time as the second medium.

In an attractive embodiment, step a) also comprises the step of preparing a third liquid medium, which comprises divalent calcium ions. As has already been explained above, the Ca2+ ions act as a crosslinking agent for the alginate which is present in the second medium. This results in a ground cover in which the alginate is crosslinked, thereby increasing the load-bearing properties of the ground cover. It should be noted that an advantageous ground cover can be obtained even without a cross- linking agent being present; in this case, the ground cover can be quickly broken down and can be easily worked into the ground.

If a third medium which comprises divalent calcium ions is used, step b), in an advantageous embodiment of the method according to the invention, comprises the following steps: bl) applying the first medium and the second medium to the ground which is to be covered, and b2) applying the third medium to the ground as obtained in step bl).

Although the media used can be applied to the ground separately or in combined form, it is advantageous for the third, calcium- containing medium to be applied to the ground separately from and after the first medium and the second medium. The first medium and the second medium, optionally in combination, are applied to the ground, after which the third medium is applied to the ground separately. As a result, the crosslinking agent calcium is only brought into contact with the alginate once the alginate has been applied to the ground, so that premature crosslinking which could occur prior to application of the medium to the ground is prevented. However, it is also possible for the second, alginate-containing medium and the third, calcium-containing medium to be combined prior to step b), if appropriate also together with the first, fibre-containing medium, in which case it must be ensured that crosslinking substantially does not occur prior to application to the ground, since a medium which contains crosslinked alginate can become difficult to process on account of its increased viscosity.

In another preferred embodiment, at least the first medium and the third medium are combined. In this embodiment, the fibres and the calcium ions are applied to the ground which is to be covered together, after which the alginate-containing medium can be applied to the ground. Accordingly, step b) of a further attractive embodiment of the method comprises the following steps: bl) applying the first medium and the third medium to the ground which is to be covered, b2) applying the second medium to the ground as obtained in step bl).

In this embodiment, the fibres and the calcium ions are applied to the ground and therefore crosslinking is not yet possible.

Then, the alginate-containing medium is applied, after which crosslinking can take place in order to obtain the ground cover in accordance with the invention.

If the media are applied to the ground separately, it is preferable for the fibre-containing first medium to be applied prior to the other media.

The first medium, or the first medium combined with the second and/or third medium, preferably contains 60/100 g of dry matter per litre of medium. If the dry matter content is higher, the medium to be applied becomes too viscous, making it difficult to pump. If the dry matter content is below 60 g/1, the medium has a relatively low viscosity, which may make it difficult to form a homogenous, continuous nonwoven. The medium preferably contains 70-85, most preferably 75-80 g of dry matter per litre of medium.

The second medium, or the second medium at least combined with the first medium, preferably comprises 2-40 w/w%, most preferably 5-15 w/w%, of alginate. The alginate preferably comprises a mixture of alginate with a high"G block"content and alginate with a high"M block"content."G block"and"M block"are terms which are well known in the specialist field; "G block"relates to a portion of the alginate molecule which comprises polyguluronic acid and forms firm gels."M block" refers to a part of the alginate which comprises polymannuronic acid and forms elastic gels. Alginates of this type are known to the person skilled in the art, for example Manugel DMB (with an M block: G block ratio of 30: 70) and Manucol DM (with an M block: G block ratio of 60: 40). Manugel and Manucol are trade names belonging to Kelco Inc. USA. The ratio of these alginates is one of the important factors in determining the strength and flexibility of the nonwoven which is to be obtained. It will be possible for the person skilled in the art, when considering the desired strength and flexibility of the ground-cover nonwoven, to determine and/or establish the correct ratio in a simple way

by selecting an appropriate combination of the G block content and the M block content in the alginate.

The third medium, or the third medium at least combined with the first medium, preferably comprises 0.1-0. 4 w/w%, most preferably 0.15-0. 25 w/w%, of Ca2+ ions in order to crosslink the alginate.

In particular if the third medium containing calcium ions is combined with the second, alginate-containing medium prior to step b), the alginate which is present will be crosslinked so quickly above 0.4 w/w% of Ca2+ ions that it will be difficult to form a homogenous nonwoven and that spraying installations may become blocked. However, if the Ca2+ ion content is below 0.1 w/w%, the crosslinking is insufficient to strengthen the ground-cover material.

The first, second or third medium, or a combination thereof, may also comprise additional agents, such as buffer materials for buffering any pH differences in the ground or the pH of different types of ground. The pH of the suspension is preferably 5-6, and the suspension is preferably buffered in this pH range. The person skilled in the art will know of suitable buffer substances, such as K2HPO4, NaH2PO. It is also possible, for example, for fillers, such as kaolin, to be included in the suspension. The suspension preferably contains 60-100 g of dry matter per litre of suspension.

As has already been indicated, a plasticizer can be included in the ground cover when the method is being carried out. A plasticizer of this type is used to prevent loss of cohesion between the biologically degradable fibres and the optionally crosslinked alginate, which may occur under high temperature and/or low atmospheric humidity conditions.

Various types of plasticizers can be used; it is expedient for the plasticizer to be selected from, for example, ethylene glycol, propylene glycol, liquid polyethylene glycol, glycerol and the like. Glycerol is advantageously used.

The quantity of plasticizer to be used is not critical; for example, quantities of 0. 1-5% based on the weight of a suspension which is a combination of the first medium and the second medium may be used, and the quantity is preferably 1-5% by weight.

The plasticizer can advantageously also be included in the third medium, which is, for example, a solution of calcium chloride or any other divalent alkaline-earth metal ion which can crosslink alginate in water. The quantity of plasticizer to be incorporated in this third medium (also referred to as the crosslinking or fixing medium) is for example 1-20%, based on the weight of the third medium, preferably 5-20%.

In a preferred embodiment, at least the first, second or third medium or a combination thereof comprises a crosslinking- retarding agent. The inclusion of an agent of this nature ensures that the alginate can be thoroughly mixed with the divalent ions without the crosslinking occurring so quickly that the mixture can no longer be processed. This is important in particular if the second medium and the third medium, and optionally also the first medium, are combined prior to step b).

A crosslinking-retarding agent allows a longer processing time to be used. Crosslinking-retarding agents are known in the specialist field. These agents are preferably selected from the group consisting of EDTA (ethylenediaminetetraacetic acid), phosphates, such as sodium tripolyphosphate, sodium hexametaphosphate, citrates, such as trisodium citrate.

As has already been indicated above, a layer thickness of 0.5-5 mm, more preferably 0.5-2 mm, is applied.

To obtain the desired layer thickness, in step b) the media are preferably applied in an amount of from 8-15 m3 per hectare of ground.

Step b) preferably comprises the step of spraying the media onto the ground which is to be covered.

As has already been explained above, the first medium, second medium and third medium can be applied to the ground separately or, if desired, may be combined with one another prior to step b). If at least two out of the first medium, second medium and third medium are applied separately, it is advantageous to use a spraying installation with two or more spray heads, in which case, by way of example, the first medium, combined with the second medium, is sprayed out of one spray head and simultaneously or sequentially the third medium is sprayed out of the other spray head. It is also possible in this way for the first medium to be combined with the third medium and sprayed out of a first spray head, while the second medium is sprayed out of a second spray head. It is also possible for the first, second and third media to be applied to the ground from three separate spray heads.

The invention also relates to a dry, pulverulent mixture for producing a ground cover which comprises alginate and biologically degradable fibres, for example for producing a ground cover according to the invention. A dry, pulverulent mixture of this type is simple to handle and market. The user merely has to add water in order to obtain a desired suspension for production of the ground cover.

In another embodiment, the invention provides a dry, pulverulent mixture for producing a ground cover, which mixture comprises a divalent calcium salt and biologically degradable fibres. It is merely necessary for an alginate-containing liquid medium, preferably an aqueous medium, to be added to this mixture so that a crosslinkable ground cover according to the invention can be formed. It is also possible for pulverulent alginate and an aqueous medium, such as water, to be added to this pulverulent mixture in order to obtain a suspension which can be applied to the ground which is to be covered.

The mixture according to the invention preferably comprises 60-98 w/w%, preferably 85-95 w/w%, of biologically degradable fibres. Furthermore, the mixture preferably comprises 2-40 w/w% of alginate, most preferably 5-15 w/w% of alginate.

In another attractive embodiment, the mixture comprises 0.4-1. 5 w/w%, preferably 0.6-1. 0 w/w%, of calcium salt, preferably an inorganic calcium salt, and even more preferably calcium hydrogen phosphate, preferably CaHPO4. It is preferable to select a calcium salt which is relatively insoluble, so that Ca2+ is only released into the suspension slowly, so that the alginate is crosslinked less quickly and therefore the suspension remains processable for a longer time.

CaHPO4. H20 is one such example.

The dry, pulverulent mixture according to the invention preferably comprises both biologically degradable fibres and alginate and a divalent calcium salt.

In a further embodiment, the mixture comprises a crosslinking retarder, as has already been mentioned above.

The mixture may also comprise a light-retarding agent, for example in the form of a dye.

The invention also relates to the preparation of a biologically degradable ground-cover suspension, comprising the step of introducing a mixture according to the invention into an aqueous medium. It is preferable to introduce 60-80 g of mixture per litre of aqueous medium, more preferably 70-85 g of mixture per litre of aqueous medium, and most preferably 75-80 g of mixture per litre of aqueous medium.

The invention will be explained in more detail below with reference to the examples, which are not intended to limit the invention.

Examples Example 1 a) preparation of dry base mix Cotton fibres 25% Wood fibres 45% Kaolin 15% Alginate mixture 10% Phosphate buffer 5% The components were mixed to form a homogenous mass. b) preparation of suspension 925 litres of water were pumped into a tank (1500 litres) provided with a stirring mechanism. 75 kg of dry base mix were suspended into this water with vigorous stirring. c) application of the ground cover the tank containing the suspension was placed on an agricultural tractor and while the tractor was driving at a constant speed, the suspension was applied to the ground via a pipe with sprayers (4 mm flat jet) over the width of the area to be covered, at a pressure of approx. 4-6 bar.

It was possible to set the desired layer thickness by means of the tractor speed and sprayer pressure.

A 5% CaClz solution was sprayed onto the first layer via a second sprayer system, parallel to the first, resulting in direct fixing (crosslinking) of the first layer.

The layer formed in this way follows the contours of the surface of the ground and therefore provides an effective cover. The layer is water-permeable and transmits light selectively depending on the pigment used.

The layer is stable during the growth time of the crop and is able to withstand a certain mechanical load.

After the growing time, the layer can be mixed with the ground, after which it is broken down by microorganisms.

Example 2 a) preparation of the dry base mix Cotton fibres 25% Wood fibres 45% Kaolin 4. 75% Alginate mixture 10% Phosphate buffer 5% CaHPO. H2O 10% Sodium hexametaphosphate 0. 25% The components were mixed to form a homogenous mass. b) preparation of suspension The suspension was prepared in the same way as in Example 1. c) use Cf. see Example 1, but without subsequent treatment with CaCl2. The first layer was applied in the same way as in Example 1, but no Ca2+-containing solution was sprayed. Unlike in Example 1, in which gelation took place immediately, gelation occurred gradually and was complete after approximately 1 hour. This gradual dulation provides'improved bonding of the covering layer to the ground. The quality and strength of the layer are similar to those achieved in Example 1.

Example 3 a) preparation of dry base mix Cotton fibres 25% Wood fibres 45% Kaolin 15% CaS04. 2H20 10% Phosphate buffer 5% b) preparation of suspension 75 kg of dry base mix were dispersed in 925 kg of water with vigorous stirring. c) preparation of alginate mix Alginate mixture 10% Wood fibres (maximum length 500 um) 90% d) preparation of alginate suspension 10 kg of mixture as described under c) were dispersed in 200 kg of water with vigorous stirring.

Stirring was continued for a further 10 minutes to obtain an optimum distribution. e) use The suspension described under b) was applied to the ground in the same way as described in Example 1).

The suspension described under d) was sprayed onto this layer, so that a thin, gelated film was formed which adhered well to the ground below, was water- pervious and after drying formed a strong, continuous covering layer which had sufficient elasticity and was resistant to tearing.

Example 4 The same procedure was used as in Example 1. During the preparation of the suspension under b) 25 kg of commercial grade

glycerol were added. Even in the event of prolonged drought (> 1 month) and high temperatures (up to approximately + 30°C), the ground cover retained its cohesion; there was scarcely any breakdown in the cohesion between the fibres used.

Example 5 A suspension was prepared in the same way as in Example 2; 20 kg of glycerol were also added during the preparation.

As in Example 4, no significant loss in cohesion of the ground cover formed in situ was observed in the event of prolonged drought and high temperatures.

Example 6 The same procedure as in Example 1 was adopted; in this case, however, glycerol was incorporated in the calcium chloride solution, in an amount of 25 g/1, as a plasticizer. As in Examples 4 and 5, excellent results were obtained.