GB2161466A - Plant growth medium containing vegetable fibres - Google Patents

Abstract

A plant growth medium comprises a fibrous substantially non-humified vegetable material which has been comminuted to a mean fibre length of less than 100 mms. Preferably, the composition also contains a digested animal waste. The invention also provides compressed and uncompressed compositions for use in the method of the invention and plant growth modules which comprise compressed bodies of the compositions in a loose fitting bag. Upon watering of the composition, it swells to provide a friable growth medium within the container.

Description

SPECIFICATION Plant growth medium The present invention relates to a plant growth medium, notably to one which comprises compressed comminuted substantially un-humified vegetable fibres.

Peat is well known as a growth medium or as a major component of such media. However, peat is a naturally occuring substance and commercially workable deposits do not necessarily exist in the areas of greatest usage. Hence, it is necessary to transport comparatively large tonnages of peat away from the bogs where it occurs to satisfy demand in other areas. Since as much as 70% of the total weight of peat can be water, this is expensive. Also, the supply of peat is finite and in some areas in nearing exhaustion.

Over the years, there have been many proposals for diluting the peat with a compatible carrier or diluent or to replace the peat entirely with a synthetic growth medium. Thus, ithas been proposed to admix the peat with a foamed plastics material or to use a mineral fibre orfoamed plastics material as the growth medium. However, these substitutes and extenders have been expensive and soften give rise to pollution problems since they do not breakdown in the soil.

I have now devised a novel plant growth medium which reduces these problems and which is readily made form materials available over a wide area of the country, thus reducing the cost and transport problems.

Accordingly, the present invention comprises a plant growth-medium which comprises compressed substantially non-humified fibrous vegetable waste material which has been comminuted prior to compression so as to have a mean fibre length of less than 100 mms.

Preferably, the compositions of the invention also contain one or more additional components, notably the solids fraction from the aerobic and/or anaerobic digestion of animal wastes.

The invention further provides a plant growth medium comprising a mixture of comminuted substantially non-humified vegetable fibres and the solids fraction obtained from the digestion of an animal waste.

The term non-humified is used herein to denote a material which has undergone substantially no conversion of the organic matter therein to humus and the invention therefore does not include peat as one of the essential vegetable fibre components of the composition. Peat may be present as an optional ingredient in the compositions of the invention, but only as a minor component, i.e. in less than 50% by weight of the total vegetable fibre constituents of the composition.

The term compressed is used herein to denote material which is subjected to a reduction in its initial volume of at least 50%, preferably the volume is reduced to less than 20% of its initial value.

The term comminuted is used herein to denote a material which has been subjected to a deliberate size reduction step so as to ahieve a desired fibre length reduction. The term is intended to exclude materials which have coincidentally been reduced in size, for example during handling, without any control on the mean fibre length achieved during that size reduction.

The invention can be applied to a wide range of vegetable fibres, but is of especial use with compressible materials comprising a mass of interwoven cellulosic fibres or to the hollow stems of crops.

Thus, the invention is of especial use in the treatment of stem or leaf wastes from the harvesting of arable or other crops and to the fibrous pulp wastes from the extraction of sugar from sugar beet. Typical materials for presentmuse include potato haulms, the leaves from sugar beet, timber felling and pulping residues, legume and grass hay and, most preferably, straws, notably those from wheat or barley. For convenience, the invention will be described hereinafter in terms of straw as the vegetable fibre.

For present use, the vegetable material preferably has a water content of less than 10% on a dry weight basis. This can be achieved either by natural drying, as when straw or hay is allowed to dry in the field after harvesting, or by force drying, as when sugar beet pulp is dried in a forced draft kiln or the like.

The vegetable material for present use is comminuted to the desired fibre length before being compressed. The comminution can be achieved in any suitable manner, e.g. by the use of a straw chopper on the combine harvester used to harvest the barley or other crop. However, it is preferred to harvest the crop in the normal manner and to obtain the straw in the form of a bale or the like which is then fed to a comminution device at the location where the plant growth medium is to be formulated.

Comminution is preferably carried out to give a fibre length of 90% less than 50 mms, as measure by passing the comminuted material over a vibrating screen with a mesh size of 50 mms.

Since the vegetable materials for present use are available over a wide area of the country as waste materials, the problems of transport are reduced and the raw materials for present use are not dependent on a diminishing source.

The plant growth medium of the invention is formed by compressing the vegetable fibres into a block or the like which can then be packed into a suitable container for transport and storage. The container can also act as the container in which plants are grown in the medium, as when a briquette of the plant growth medium is put up in a loose plastics bag or the like for use as a plant growth module when the medium therein is wetted up to form a loose and expanded growth medium in the bag.

Compression can be achieved by any suitable method, as when the vegetable fibres are extruded under pressure or are pelletised in a rotary or other press to form blocks or briquettes. As stated above, compression is carried out to achieve a reduction of at least 50% in the initial volume of the material being compressed. Preferably, the material is compressed to from 5 to 20% of its initial volume and this will usually require a pressure of from 5 to 50 tons per square inch.

At these pressures, little or no added binder is required to retain the compressed form once the material leaves the press. However, if desired, the compositions of the invention may contain other materials which enhance the stability of the compressed product and/or its use as a plant growth medium. Thus, the compositions can contain fertiliz ear salts and/or resin binders notably when incorporated into the straw before comminution and compression to aid intimate admixture therewith.

However, it is particularly preferred to incorporate the solids fraction obtained from the aerobic and/or anaerobic digestion of animal wastes into the compositions of the invention. These provide a binding and bulking effect as well as providing a source of bacteria for the break down of the vegetable fibres, e.g.in the soil after use,-without imposing a major requirement for-bacterial nutrients on the growth medium, since the organic matter therein is already at least partially digested as compared to farmyard manures in which little digestion- has occurred. Also, in some cases the animal wastes contain keratinous fibres which aid the drainage and capillary action of the plant growth media containing them and may supply slow release nitrogen to plants grown therein.

The animal wastes for present use can be derived from a wide range of animals, including sewage or domestic refuse sludhes. Preferably, the animal waste is that obtained from stock houses and farmyards, e.g. chicken houses or, most preferably, from pig houses. Suchwastes typically also contain animal bristles and/or hairs and the preferred wastes for present use are characterised in that they contain keratinous fibres which, as state above, I believe aid drainage ofthe growth media of the invention and of soil into which the compositions are incorporated as soil structuring aids. For convenience, the invention will befurther described in terms of the use of the waste from pig husbandry, notably that from the intensive rearing of pigs.

The animal waste, usually in the form of a slurry obtained directly from the animal house, is subjected to digestion so as to reduce it B.O.D. and C.O.D. and total solids so as to render it suitable for use in the present invention. Typically the digestion is carried outto reduce the B.O.D. of the waste to below 50% of its initial value.

The digestion is typically carried out in a closed vessel under anaerobic conditions to yield methane gas, a liquid phase and a solids phase for present use.The digestion can be carried out using conventional techniques and equipment The digested-material is removed from the digestion vessel either continuously or intermittently and the solids fraction separated off in a settling tank or by a filtration operation. The solids fraction typically contains less than 30% by weight liquids and can be dried before use in the present invention if desired.

Thus, the solids can be force dried in a kiln or the like or can be naturally dried in heaps spread on the floor of a barn or other building over which airflows to remove water by evaporation. Since the bulk of the fluid phase is separated off from the solids fraction before use in the invention, the build up of toxic heavy metal salts therein is reduced.

In a particularly preferred method of operation, pig house waste is digested under anaerobic conditions in a tower like vessel undergoing agitation using the methane generated by the digestion of the waste.

Part of the contents of the tower are displaced as fresh material is fed to the tower. The displaced material is passed through a screen, typically with a mesh size of from 0.5 to 5 mms, to remove the solids fraction for use in the compositions of the invention.

The solids fraction is then naturally or force dried to a water content of less than 10 % by weight on the dry matter content.

The solids fraction can be used directly as such or can be admixed with other ingredients of value in plant growth compositions, for example fertilizers, pesticides and the like, for incorporation into the vegetable fibre component of the compositions of the invention.

The preferred compositions ofthe invention are made by admixing the animal and vegetable waste materials in the desired proportions using any suitable technique. Thus, straw and puverulent digester solids can be fed to a dry mixer or to a chopper in which the straw is chopped up to the desired particle size. It is preferred to use from 1 to 5, notably 2 to 3, portions by weight of vegetable material per 0.2 to 2, notably about 1, portions by weight of digester solids. It is also preferred that the resultant mixture have an overall water content of less than 10% on a dry weight basis.

The compressed vegetable fibre products of the invention find use as a plant growth medium directly or, most preferably, when packed in a loose container, e.g. a plastics bag orthe like, which allow the contents thereof to expand on watering to form a loose plant growth medium within the container.

Where the compositions contain animal wastes as well,they can be used as plant growth media directly without compression thereof, e.g. as soil substitutes, extenders or conditioners. However, it is preferred that these compositions also be subjected to compression to form compact products which can be packed in a loose container for transport and storage, but which expand upon watering to form a plant growth module containing a loose plant growth medium. Typically, the compressed products of the invention are put up as briquettes or blocks of the compressed plant growth medium in a container having a filled volume of from 35 to 50 litres so as to provide a growth module suitable for the growth of 3 or 4 tomato plants therein. The compressed blocks or briquettes will usually provide frdm 3 to 5 Kgs of growth medium on a dry weight basis in the container.

Accordingly, the invention also provides a plant growth module comprising a container having a filled volume of from 35 to 50 litres containing a compressed plant growth medium capable of expansion upon watering to provide a loose plant growth medium in the container, said medium comprising substantially non-humified vegetable fibres comminuted to a mean particle size less than 100 mms, optionally in admixture with the solids fraction of a digested animal waste, preferably contaning keratinous fibres.

The invention further provides a method for raising plants which comprises planting plants in a composition of the invention, preferably after watering thereof to produce a loose material.

The term loose is used herein in respect of the watered compositions of the invention, notably of the compressed compositions, to denote that the composition is penetratable by the roots of plants end preferably is a free flowing substantially aggregate free material. Where a compressed composition is watered, the resultant product may be in the form of a soft friable body which can be readily broken down to give a free flowing product.

The compositions of the invention find use as plant growth media. Since they contain only low amounts of available plant nutrients, there is reduced risk of root scorch with young plants as compared to high nutrient content materials. Due to the presence of animal hairs therein, the compositions are free draining and there is thus reduced risk of damping off of young plants sown in the conpositions. Since the compositions are made from widely available materials, they can be readily made close to the intended site of use, thus reducing the transport problems encountered with peat based materials. Furthermore, since the compositions can be made in a substantially dry form, any transport costs which may be required are reduced.

Where the products of the invention are put up in the form of compressed cylinders, blocks, briquettes or the like, such products offer the user a compact and comparatively lightweight growth medium or growth module which the user can readily carry, in contrast to conventional peat-based products which are often bulky and heavy.

The invention will now be illustrated by the following Example in which all parts and percentages are given by weight unless stated otherwise.

Slurry from a pig husbandry unit was pumped at the rate of 700 litres per hour to a digestion tank in which the slurry was bacterially digested at 35"C to give a liquid of reduced B.O.D. and C.O.D., methane gas (which was recycled through a sparge pipe at the base of the tank to agitate the contents of the tank) and a solid phase which contained digested solids and pig bristles. Part of the contents of the tank (700 litres per hour) were allowed to overflow into a filtration pit as fresh slurry was fed to the tank. The filtration pit contained a wire mesh screen (aperture size 2 mms) which separated the solids from the liquid phase.The liquids were run off to a storage pit and the separated solids were collected and spread out on the floor of a barn or the like to allow the liquid content thereof to reduce to below 10% on a dry weight basis by natural evaporation.

The dried solids were mixed with 2 parts of barley straw, chopped to a mean fibre length less than 2.5 cms. The resultant mixture was fed to a briquetting press where the mixture was formed into cylindrical plugs under a pressure of 40 tonnes per square inch which reduced the initial volume of the mixture to approximately 20%. The plugs were packed three into a conventional plastics growing module bag to give a product weighing 3 to 5 Kgs. The product could be readily transported and stored by a householder.

When required for use, the contents of the bag are wetted up with 45 litres of water. This causes the contents to swell and break up into a friable free-draining plant growth medium in which tomatoes or other plants can be grown as with a conventional plant growth medium. If desired, the plants can be fed with nutrients, eg. as an aqueous drip feed or the like, during their growth. Altnatively, the contents of the bag can be dug into the soil to act as a soil structuring agent, either before or after watering.

Claims (10)

1. A method for raising plants which comprises planting plants in e composition which comprises a fibrous substantially non-humified vegetable material which has been comminuted to a mean fibre length of less than 100 mms.

2. A method as claimed in claim 1 wherein the composition is in the form of a compressed body of the composition in a loose container and the composition is watered to cause the composition to expand within the contsainer.

3. A plant growth medium for use in the method of claim 2 which comprises compressed substantially non-humified fibrous vegetable waste material which has been comminuted prior to compression so as to have a mean fibre length of less than 100 mms.

4. A composition as claimed in claim 3 which also comprises the solids fraction from the aerobic and/or anaerobic digestion of an animal waste.

5. A plant growth medium for use in the method of claim 1 which comprises a mixture of comminuted substantially non-humified vegetable fibres and the solids fraction obtained from the digestion of an animal waste.

6. A composition as claimed in claim 5 wherein the composition has been compressed to a volume which is from 5 to 20% of its initial volume.

7. A composition as claimed in any one of claims 3 to 6 wherein the vegetable matter is a straw.

8. A composition as claimed in any one of claims 4 to 7 wherein the animal waste contains keratinous fibres.

9. A composition as claimed in claim 5 wherein the vegetable and animal wastes are present in dry weight ratios of from 1 to 5:0.2 to 2 respectively.

10. A plant growth module comprising a compressed body of a composition as claimed in any one of claims 3 to 9 in a loose fitting plastics bag having a filled volume of from 35 to 50 litres.