GB2249463A - Device and method for irrigating plant roots - Google Patents

Abstract

Plants generally prefer water and other liquids such as fertilizers to be applied at root level. By using an irrigation tube 1 buried in soil adjacent to a plant, liquid from within the tube percolates radially through foraminous ports in the lower section of the tube. The ports 2 are preferably formed by a number of holes occluded by porous felt-like material 6 in the wall of a plastics tube sealed at its lower end with a bung 4. A removable cap 5 to prevent foreign bodies from falling in the tube may be located on the open upper end of the tube which projects above the soil surface. <IMAGE>

Description

TITLE: DEVICE AND METHOD FOR IRRIGATING PLANTS The invention particularly relates to a tube inserted into the soil adjacent to the plant and through which liquid percolates slowly into the soil.

BACKGROUND TO THE INVENTION: When plants, shrubs or tress (for convenience denoted generally by the term plant hereinafter) are planted, problems arise in maintaining the correct wetness in the soil around the root system of the plant. Typically, water is applied to the soil surface around the plant and this percolates through the spaces between the soil particles to reach the root system. However, much of the water is lost within the soil before it reaches the deep roots of the plant; and often the top layers of the soil can become compacted and prevent the penetration of water, which is then lost through run off. Similarly, where fertilizer or other plant nutrients are applied to the soil, much is lost before it is taken up by the plant root system.

In order to reduce these problems, it has been proposed, see for example US Patents 3,755,966 and 4,726,143, to sink a tube into the soil amongst the root system of a tree or shrub. The upper end of the tube is accessible to a gardener to feed water or nutrient solution to the tube.

The base of the tube has a plurality of openings which allow water and nutrient solution to seep into the surrounding soil at about the level of the root system. However, such devices are relatively costly and of comparatively complex construction and require to use of a gravel or similar bed within the tube to prevent flushing of solids from the tube through the basal openings. The need to use such a gravel bed reduces the usable volume of the tube.

With such known devices any erosion of the soil takes place below the tube which may cause it to sink into the ground below the level required for successful irrigation of the root system.

The method and device according to the present invention for irrigating plant root systems provides a radial flow of liquid. Also by controlling the rate at which the liquid percolates into the soil the risk of erosion is reduced and the need for gravel within the tube is eliminated.

SUMMARY OF THE INVENTION According to the present invention there is provided a method for irrigating the root system of a plant growing in soil, providing a reservoir of liquid in a hollow tube located substantially upright in the soil adjacent to the root system, restricting the flow of the liquid from the tube through a filter material so that it percolates radially into the soil only along a first section of the tube remote from the surface of the soil.

According to a second aspect of the invention there is provided a plant root irrigation device comprising a hollow tube open at one end and having a foraminous first section through which liquid can percolate in a substantially radial direction relative to the longitudinal axis of the tube.

According to a further aspect of the invention there is provided a plant root irrigation device comprising a hollow tube having a first section and a second section, in which the second section is interjacent a first open end of the tube and the first section, and in which the first section is interjacent the second section and the other end of the tube characterised in that the first section includes a number of ports containing a filter material arranged to permit liquid to percolate radially through the ports from within the tube to the soil so that, in use, the roots of a plant located close to the device are irrigated.

Preferably the tube is of plastics material which is provided with a plurality of apertures in the first section which extends from the closed end of the tube for up to 35% of the length of the tube. Preferably the filter material is a continuous sleeve supported on the outside of the tube along the entire length of the tube. However, the filter material may be provided in discrete patches across each of the apertures. Alternatively, the entire first section of the tube may be formed from filter material providing it is sufficiently rigid to retain its tubular form when used.

With such an arrangement the entire second section of the tube forms the port through which the liquid percolates. It has been found that a suitable filter material is a nonwoven felt-like sheet of synthetic fibres as produced in Denmark and distributed in the United Kingdom under the trade name Fibertex Geotextiles by Tex Steel Tubes Limited.

By selecting the grade of filter material the rate of flow of liquid into the soil may be controlled. Preferably the filter materials restricts the flow of liquid into the soil to a slow weep, so that erosion of the soil around the device is minimised.

It will be appreciated that the liquid may be water or a nutrient or other horticultural solution which is slowly released into the soil close to the root system.

The tube may be plastics, metal, ceramic or other suitable tubing material having a circular, square or other cross sectional shape. For convenience the invention will be described hereinafter in terms of a right circular cylindrical tube. The open upper end of the tube may be provided with a cap to prevent soil or other extraneous matter from accidentally entering the tube. The cap also prevent evaporation of the liquid. Preferably the cap is a push fit on to the end of the tube but it will be appreciated that, if necessary, it may be screwed or otherwise clamped in position. If desired, the uppermost end of the tube can be provided with an external shoulder to seat the tube at : a desired depth in the soil.

Alternatively, the first section of the tube may be provided with a number of rims or, in the case where the filter material encases the entire tube, the filter material on the first section of the tube may be printed with lines indicating various depth levels from the remote end of the tube, or from the level at which the main flow of water occurs.

The lower end of the tube is closed by a transverse member, or bung to retain the liquid in the tube. If desired this lower end wall formed by the bung may also contain apertures forming ports across which filter material is located to allow the liquid to percolate slowly therethrough. Although this is not the radial flow preferred in most applications there are certain applications which may benefit from axial flow also. It is preferred that the bung is removable so that, if necessary, the interior of the tube can be cleaned, or so that a porous bung may be inserted when-required.

The side wall of the tube is provided with apertures in the form of axial or transverse slots although, preferably, the apertures consist of eight diametrically opposed holes four of which are positioned immediately adjacent to the bung and the other four of which are spaced at a distance from the bung depending upon the depth of stratum of soil which it is desired to irrigate. It will be appreciated that more than two levels of holes may be provided and that they may be vertically aligned or staggered. In certain circumstances, it may be preferred to provide the holes only over a segment of the tube so that the water percolates from the tube radially over an arc which embraces the root system of the plant.

Preferably the tube is formed from a plastics material which is not affected by water or horticultural liquids. Such materials may be thermoplastic materials such polyvinyl, polyalkylene or polystyrene homopolymers or copolymers such as are used in the construction of plastic drainage or land drainage pipes.

The apertures serve to constrict the flow of liquid from within the tube into the soil. The flow is further constrained by the filter material. The optimum size of the apertures and the selection of the grade of filter material will therefore depend upon the desired liquid flow rate and the nature of the type of flow required. Typically, the apertures are diametrically opposed slots from 0.5 mms to 5 mms wide and extending over the lower portion i.e. the second section, of the tube. The slots may extend for up to 35% of the length of the tube and, typically, the length of the slots may be up to 150 mms but preferably extend from about 20 mms from the end of the tube to about 125 mms from the end of the tube.

The tube may be provided with filter members which restrict the flow of water or nutrient solution within the housing to the surrounding soil through the apertures. The filter members may be provided by individual patches of suitable material glued or otherwise affixed over each of the apertures. However, it is preferred to provide the filter member as a sleeve member which can be internal, or more preferably external, and which is a close fit upon the wall of the tube. The sleeve can thus be formed as a sleeve of a foamed or porous plastic, ceramic or other suitable material which is a push fit within or externally upon the tube. However, it is preferred to form the sleeve member with a pore size which decreases progressively with the radial distance from the tube longitudinal axis.

Preferably, the pore size is smallest at the radially outward face of the sleeve member. This can be achieved by forming the sleeve from a plastic material which has been expanded progressively using techniques known in the plastic foaming art. Alternatively, the sleeve member can be formed as a laminated material from layers of material having the desired pore sizes. Thus, for example, the sleeve member can be formed from an inner layer of coarse felted coconut or other fibrous material and one or more outer layers of felted finer fibrous material. A particularly preferred filter material for present use is a non-woven sheet of polymeric fibres, notably of polyethylene or polypropylene fibres. In an alternative embodiment the porous material may be self supporting which obviates the need for a plastics support tube.

The optimum sleeve member for present use will depend upon the size of the tube and the head of water held within the tube as well as the soil conditions in which it is to be used. - However, satisfactory results will usually be achieved with a sleeve member which satisfies the following test. The sleeved tube is filled with water to its maximum operating level and the tube is suspended in air to allow water to drain freely through the apertures and the sleeve member. The sleeve member should reduce the flow of water out of the apertures to the point at which the water does not jet from the apertures but weeps down the exterior of the sleeve. Typically, the sleeve member will reduce the rate of flow of fluid from the tube to from 0.5 to 15 centilitres of fluid per minute per square cm of the wetted area of the sleeve member, preferably to from 2 to 10 centilitres.

The use of the sleeve member to regulate the flow of water through the apertures in the tube wall enables erosion of soil around the buried tube to be minimised; enables comparatively large apertures in the tube wall to be used, which greatly facilitates manufacture of the tube as compared to fine aperture tubes; and avoids the need to use gravel or other beds within the tube, which restrict the usable volume of the tube for holding water or nutrients.

The tube and sleeve member assembly can readily be made using conventional techniques. However, a particularly preferred method of fabrication is to form a tube having the apertures and the sleeve member extending throughout its length, for example by winding a suitable fibrous filter member onto a continuous length of land drainage or similar pipe having apertures throughout its length. Tubes for use in the invention can then be cut from such a continuous length.

It is preferred, as indicated above, that the apertures should be located or be effective only at or slightly above the level of the root system so that water or nutrient solution is not released into the upper soil levels significantly above the root system where it might be lost to the root system. This is achieved by locating the apertures in the basal portion of the tube. However, where the apertures extend beyond this, as when the tube is cut from a continuous length of wrapped apertured tube as described above, the effective length of the apertures will need to be reduced so that fluid does not drain through the upper portion of the tube wall. This can be achieved by sheathing the required length of the tube with a water impervious material to prevent escape of fluid from the sheathed length of the tube.The sheathing can, for example, be achieved by fitting a plastics or similar sleeve over the outside of the filter sleeve so that the plastic sleeve extends from the upper end over the desired, say, 70% of the length of the tube. The plastic sleeve can then be heat shrunk onto the tube to hold it in place and prevent release of fluid over the sheathed length of the tube.

In use, the tube carrying the filter sleeve and optionally the sheath where necessary to reduce the effective length of the apertures is buried to the desired depth in the soil, peat or other growth medium in which the plant is growing or to be grown. The upper end of the tube is exposed at or above soil level, so that the cap or other top closure can be removed and water, solid nutrient or nutrient solution can be charged to the interior of the tube. The tube can be supplied already charged with a suitable particulate nutrient, for example a slow release nutrient of any suitable type. Alternatively, any nutrient, pesticide, plant growth regulant or other horticultural liquid can be provided in solution in the water or other fluid fed to the tube as required.

By virtue of the combination of the apertures, the sleeve member and any sheathing member, fluid does not flow freely out of the tube into the soil, but percolates radially slowly into the surrounding soil at a predetermined distance below the soil surface so as to minimise erosion of the soil around the tube. By virtue of the length of the tube and the positioning of the apertures and any sheathing member, the water and nutrients are delivered into the soil at the level of the root system of the plant and are largely made available to the plant and although there is vertical travel of liquid in the soil of a small amount of the liquid very little is lost in the upper layers of the soil or by way of run off. By locating the tubes within the root plan area of the plant, it is possible to adjust the nutrient fed to one plant independently of that fed to another adjacent plant.

DESCRIPTION OF THE DRAWINGS: The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a cross section through a plant root irrigation device; Figure 2 shows an alternative form of aperture to tube for the device of Figure 1; Figure 3 shows the device insitu within a plant root system; and Figure 4 shows graphically the relationship between depth under the soil surface and water seepage from the device.

Referring now to Figure 1 of the drawings the device comprises a length of plastics tube with apertures in the form of holes 2 as shown in Figure 1 or slots 3 as shown in Figure 2 cut in the lower end of the tube. The tube may be formed of PVC or polyethylene. Preferably there are eight holes each of 5 mm diameter formed on two levels four centimetres apart. The lower set of four diametrically opposed holes are adjacent to a plug or bung 4 which seals the lower end of the tube 1. The upper end of the tube l is open but may be sealed by a demountable push fit cap 5. The internal diameter of the tube 1 is 57 mms and the wall thickness is 2 mms. The apertures 2 are drilled at 16 millimetres and 46 millimetres respectively from the end of the tube.Each aperture is 20 square millimetres so that the ratio of the wall area of the tube to aperture area is approximately 44:1.

The tube 1 is covered with a foraminous felt-like material either in the form of an external sheath 6 as shown in Figure 1 or an internal sheath or alternatively patches which may be stuck over the apertures 2 or slots 3. The sleeve material 6 is preferably a non-woven synthetic material sold under the trade name Fibertex Geotextiles as distributed in the UK, by Tex Steel Tubes Limited. By selecting a suitable grade of Fibertex Geotextile material it is possible to restrict the flow of liquid into the soil so that it percolates slowly into the soil surrounding the roots to be irrigated. In the form of construction shown in Figure 1 the sleeve 6 has been wound continuously upon the outside of the tube 1, for example, using conventional land drain wrapping techniques.

If apertures are provided along more than the lower third of the tube, or if the slots extend beyond this limit it is possible to inhibit the flow by masking the apertures in the upper section of the tube. This may be achieved by fitting a plastics sheath around the exterior of the sleeve 6 or by providing a close fitting tube within the tube 1 to close the upper apertures. The open apertures 2 form a port through which liquid such as water, plant nutrient or other horticultural liquid which is poured into the top of the tube percolates through the filter material of the sleeve 6 into the soil.

Referring now also to Figures 3 and 4, Figure 3 shows an irrigation device 7 mounted substantially vertically in the soil surrounding the root system 8 of a plant. Figure 4 illustrates graphically the seepage of liquid from the tube 7 into the soil. The vertical axis represents the depth D to which the device is buried. The horizontal axis S represents the seepage volume at varying depths. Graph 9 represents the seepage from the upper level of apertures which, when combined with the graph of seepage 10 from the lower level of holes provides the graph 11 illustrating the total seepage from the device. It will be seen that although some of the liquid percolating through the filtered ports flows in a vertical direction the majority of the liquid is distributed radially at the level of the apertures.

In operation, the tube is placed vertically close to the root system of a plant. Liquid is introduced into the tube through the open upper end and, if necessary, the upper end is then capped to prevent foreign material falling into the tube. The size of apertures and the restriction to flow provided by the foraminous material determines how quickly the liquid percolates into the soil. This will determine how frequently the tube requires re-filling with liquid.

The tube can be supplied empty or with the charge of slow release fertilizer granules which gradually dissolve in water fed to the tube. It will be appreciated that a number of irrigation devices may be positioned around the plant to encourage even distribution of the root system.

Although the invention has been described with reference to a plastics tube it will be appreciated that the tube 1 may be formed from ceramic or other self-supporting material sufficiently rigid to provide a support for the flexible filter material. However, it is possible to use a foraminous material which has sufficient rigidity to obviate the need for a further support tube. The irrigation device may be used for different plants whose root systems occur at different depths. It is therefore possible to have one or more flanges or other indicia such as printed level marks on the upper end of the tube to act as depth gauges for recommended depths at which root growth is to be encouraged.

In a particular embodiment of the invention the circular ports of 0.3cm radius were located at two levels 4cm apart in the axial direction of the tube. The ports had a total area of 2.63cm and the four ports were symmetrically provided at each of the two levels to provide even radial flow around the entire circumference of the lower section of the tube. The internal bore of the tube was 5.7cm, and the total length 30cm having a 0.2cm wall thickness. The lower level of ports was located 1.7cm from the end of the tube so that when the bung was inserted 1.2cm into the lower end of the tube, the lower level of ports was just above the bung so that in use, the total capacity of 0.7 litres can slowly percolate into the soil.

It has been found that the flow rate may be varied by using other grades of Fibertex material from 2.31 centilitres per minute to 6.93 centilitres per minute. The choice of material will depend upon the particular circumstances of use, for example soil structure and composition, general climatic conditions and the plant to be irrigated.

It will be appreciated that by extending the width or the length of the tube the volume of liquid which is held in the reservoir formed by the hollow tube may be varied as required. -Although the tube according to the preferred embodiment is a right circular cylindrical tube in which the apertures are equally spaced around the circumference of the tube at a number of levels, the tube may be of any cross section and the apertures may be provided at only a single level or only over a limited arc of radius so that the liquid may be directed in a selected radial direction from the device.

It will also be appreciated that the device may be removed from the soil and cleaned for re-use as required.

Claims (16)

What I claim is:

1. A plant root irrigation device comprising a hollow tube open at one end and having a foraminous first section through which liquid can percolate in a substantially radial direction relative to the longitudinal axis of the tube.

2. A plant root irrigation device comprising a hollow tube having a first section and a second section, in which the second section is interjacent a first open end of the tube and the first section, and in which the first section is interjacent the second section and the other end of the tube characterised in that the first section includes a number of ports containing a filter material arranged to permit liquid to percolate radially through the ports from within the tube to the soil so that, in use, the roots of a plant located close to the device are irrigated.

3. A device as claimed in Claim 1 or Claim 2 in which the tube is a self supporting structure.

4. A device as claimed in Claim 1 or Claim 2 in which the tube consists of an apertured support tube closed at one end and supporting a sleeve of porous material.

5. A device as claimed in Claim 4 in which the sleeve of porous material is supported on the outside of the tube.

6. A device as claimed in any preceding claim in which the tube is constructed of plastics material.

7. A device as claimed in any preceding claim in which the tube is a right circular cylinder.

8. A device as claimed in any preceding claim including a cap demountably mounted on the open end of the tube.

9. A device as claimed in any preceding claim in which the tube is provided with one or more indicia to mark the depth to which the tube is to be buried in the soil.

10. A device as claimed in Claim 9 in which at least one of the indicia is a flange.

11. A method of irrigating the roots system of a plant growing in soil, comprising providing a reservoir of liquid in a hollow tube located substantially upright in the soil adjacent to the root system, restricting the flow of the liquid from the tube through a filter material so that is percolates substantially radially into the soil only from a first section of the tube remote from the surface of the soil.

12. A method as claimed in Claim 11 in which the first section of tube is within the lowermost third of the tube.

13. A method as claimed in Claims 11 or 12 in which a nutrient or horticulturally active ingredient is added to water to form the liquid in the tube.

14. A method as claimed in Claims 11 to 12 in which the rate of percolation of the liquid into the soil is selectable.

15. A method of irrigating the root system of a plant growing in soil substantially as hereinbefore described with reference to the accompanying drawings.

16. A device substantially as hereinbefore described for use with the method as claimed in any of the Claims 11 to 15.