AU2010202359A1 - Soil beds - Google Patents

Description

Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (ORIGINAL) Name of Applicant: COLIN AUSTIN Actual Inventor(s): COLIN AUSTIN Address for Service: SANDERCOCK & COWIE 180B SLADEN STREET CRANBOURNE VICTORIA 3977 Invention Title: SOIL BEDS Details of Associated Provisional Application(s): No(s): Australian Provisional Application No. 2009902826 Filed: 10 June, 2009 The following statement is a full description of this invention, including the best method of performing it known to me: - 1- - la TITLE: SOIL BEDS FIELD OF THE INVENTION 5 This invention concerns a method of using water for irrigation, a system for plant propagation using irrigation, a method of recycling waste organic material to improve soil quality for embedding carbon into the soil and reducing atmospheric carbon, a method of reusing wastewater and a kit for assisting the construction of the system.

-2 BACKGROUND OF THE INVENTION In conventional irrigation water any water close to the surface will quickly evaporate so a proportion of the irrigation water will be lost by evaporation, particularly if only a small 5 irrigation is applied. This can be reduced by applying a larger irrigation however any water passing the root zone will be lost to the plant and may cause contamination of the ground water and river systems. If there is a subterranean impervious clay layer, the percolating water sinks through the 10 soil and forms an underground pond of stagnant, nutrient rich water. This would turn anaerobic and remain a putrid mess inhibiting plant growth. Roots need air as well as water and the best result is when water occupies the air spaces in the soil during percolation and the spaces refill with air as the water drains lower. 15 SUMMARY OF THE INVENTION A method of subterranean irrigation, comprising excavating a trench, lining the trench with a waterproof liner, at least partially filling the lined trench with coarse, void-creating organic waste, covering the waste with soil intended to support plants, and adding water 20 to the subterranean organic waste. The organic waste produced by photosynthesis and hence already containing captured atmospheric carbon dioxide is covered with water and decomposes slowly to integrate with the soil, under semi anaerobic condition with anaerobic bacteria and fungi, thus making a method of capturing carbon from the atmosphere. Accordingly, the lignin in the coarse organic waste is prevented from entry 25 into the rapid part of the carbon cycle and instead is utilised by fungi to grow extensive hyphae which lock up carbon. Some of the lignin composts slowly to long chain cellulose derivatives. Plants, bacteria and fungi trap atmospheric carbon in a quantity which is about thirty times the quantity of carbon in manmade emissions. 30 The trench may be 200-300mm deep if a raised soil bed is to be built and 600-800mm deep if a ground level bed for orchard or commercial operations is required. The dimensions of the trench depend on the intended use. If the lining only extends part way -3 up the sides of the trench, the soil on both sides of the trench will be wetted by wicking. The waste can be as coarse as twigs and weeds from suburban mulchers and mill waste woodchips which are of irregular shape and consequently do not pack together, giving 5 a large void content. This saturate coarse aggregate can increase the water capacity by up to five times that of regular soils with rounded particles at field capacity. The organic matrix allows water to wick up to the overlying soil. Inorganic materials such as sand or gravel aggregate can also be used but are not as effective in their wicking action. 10 If the irrigation occurs in marginal rainfall areas, extra water capture is possible by this method if the liner is extended out of the trench as an inclined margin just below ground level. In this way rainwater percolates downwards until it contacts the liner extension and runs into the trench by gravity. The entire margin around the trench may be utilised in this way but this requires more work in preparing the site and checking levels to ensure 15 that the water will collect in the trench. The result is that plants which normally die as a dry spell ensues do not die in the area above the trench. They receive water from the subterranean cache and are more likely to live through intermittent dry spells. In a commercial operation where some but insufficient water is available for irrigation, 20 the trench may be given periodic stored water by laying a pipe in the trench before adding the coarse organic waste. An agricultural pipe of flexible construction with multiple perforations is suitable, however a pipe with slots in the base only is less likely to become clogged. It is useful to lay this substantially level with the ends raised, ending at or just above ground level so that the water level can be inspected when the liner is given a 25 substantial volume of water. The water stays confined by the liner and forms a subterranean pond with much of the volume occupied by the immersed organic waste. The evaporation from such a bed is a fraction of what it would be if the bed had been wetted by water spraying or flooding. 30 If rapid growth is required such as for growing vegetables and night time root temperature is important the irrigation method could include building a soil layer on the coarse waste layer to form a raised bed above surrounding soil levels. Raised beds are -4 particularly beneficial in region subject to wet conditions or flooding. As an alternative to making the wicking bed in the ground the entire system may be enclosed in a box or other suitable container. 5 The porosity of the soil layer whether raised or at ground level may be improved by the addition of suitable types of earthworms. Worms of the Amyuthus species which is a large, deep-feeding worm, will burrow and produce a sponge-like texture in the bed. This improves permeability and assists C0 2 capture. 10 Fungi can also improve soil quality by forming an aerated structure and fungi will decompose material with less emission of carbon dioxide than aerobic bacteria. Surface tension allows soils to hold a certain amount of moisture against the pull of gravity. Water in the larger pores is pulled down by gravity while the water in the small 15 pores, where surface tension is higher, can resist gravity. The equilibrium amount of water held in the soil is called the field capacity and varies widely depending on the pore size. The finer the pore size the more water can be held; hence clays hold far more water than sand. 20 On the other hand plants have to pull water out of the soil and again the finer the pore size the more difficult it is for the plant to extract water. The wilt point sets this lower limit and generally the difference between field capacity and wilt point, (the readily available water) does not vary that much between soil types and is typically of the order 25 of 10%. The wicking bed uses an impervious water barrier to form an underground pond or reservoir. In this pond the soil is saturated e.g. all pores are full of water. Whereas the large pores are normally empty of water they are now full. This water in these large 30 pores, with weak surface tension forces, can now readily wick upward by the action of surface tension to wet the soil above the pond.

-5 Here the soil is not saturated but moist with a gradually reducing moisture content above the pond. Water will generally wick upwards about 300mm after which surface tension can no longer lift water any further. Plants need a combination of air and water in the soil so in there is always a level which has just the right combination of air and water for 5 maximum growth. Wicking beds work best if the medium in the pond is coarse with a large pore size, waste organic material is often used as it can hold a large amount of water when saturated but allows water to wick up through the organic material. A wicking bed may have two 10 zones, the pond itself with large pores and the layer above with finer pores. A drainage system must be incorporated to drain off any excess water so the soil above the bed does not become saturated for any length oftime. A particularly effective method of ensuring drainage is to enclose the upper growing region in a porous medium such as 15 shadecloth. This allows a large area for the water to escape from in times of heavy rain and also allows air to permeate the soil in normal conditions. The permeable membrane used to enclose the soil may be in the form of a raised bed above the normal ground level or the upper portion of a wicking box as shown in the attached drawing. 20 In one version a porous medium is placed in the bottom of the trench to allow water to flow along the trench, this could be a conventional drainage pipe (ag pipe), but could equally be stones, rocks, sticks or any porous soil or even a readily available local material such as bamboo or bubble film to distribute water through the wicking material when required. When using stones it is advisable to cover the stones with a plastic sheet 25 to prevent soil silting up the spaces. One particularly effective method of transporting the water and increasing the water holding capacity is to use any form of container with an open bottom, such as a pipe split along its length or perforated as shown in the enclosed drawing. The trench is backfilled with soil, preferably containing a high organic content and vermacast (worm casting plus eggs). The trench is then partially or 30 completely filled with water which runs through the porous medium. The trench may be divided into horizontal sections by a small barricade so water only -6 flows over into the next section when the first section is filled. This gives a cascade effect to ensure that water is flushed from bay to bay to give maximise flushing. In a second alternative version as an alternative to using a porous medium is to use either 5 a surface pipe with regular spaced holes or surface furrow to ensure the water is distributed along the trench. Surface tension or wicking forces will allow the water to soak up and along into the surrounding soil so irrigating any nearby plants. This wicking action is significantly 10 enhanced by using organic material and worm casts in the soil. A typical configuration of the wicking bed is some form of container or waterproof membrane in the ground which is capable of storing water. It is also possible to form a waterproof underground container by compacting heavy clay in the base of the trench or 15 mixing a small percentage of cement mix with the soil. An inlet pipe will deliver water to this container, preferably to the bottom of the container so that the water level rises from below during the filling process. 20 The top of this container will generally be positioned below the normal surface of the soil, the depth below the surface may typically be 100mm but may be smaller or larger for different sized plants. One purpose for positioning the container below the surface is to provide a means of the water to drain away such that the roots are not immersed in water for any period of time. More effective drainage can be obtained by raising the 25 upper layer above ground level to form a raised bed which may be enclosed by a porous medium such as shadecloth. Alternatively a drainpipe may be fitted into the side of the container such that excess water can drain away without the roots being submerged in water for any length of time. 30 A common application is to cascade wicking beds so that the drainpipe from one bed forms the inlet pipe to the next bed.

-7 In normal use the plants will access the water by a combination of water wicking up from the reservoir of water below and the roots growing down to the water level. The preferred operation is that the surface soil is dry to prevent evaporation of water. 5 With young plants or small seedlings it is desirable to provide water closer to the surface while their root systems develop. While this water may be provided by conventional overhead watering, an improved method is to temporarily close the drainpipe while the bed is being filled with water such that the entire depth of the soil is flooded. 10 Once the flooding is completed, the drain can be opened to allow the excess water to drain away. In addition to the propagation of seeds and very young plants, this process of flooding and draining can have significant horticultural benefits. For example, the flooding of the 15 soil expels all air and gases, while the draining of the water sucks fresh air into the soil. It is known that plants need a supply of oxygen to the roots systems and that certain gases normally developed in the soil such as carbon dioxide and ethylene act as inhibitors to plant growth. This process of flooding and draining replaces such gases with oxygen. 20 It has also been found that certain crops, particular root crops with bulbous tubers such as radishes turnips etc., will benefit and show additional growth by this periodic flooding and draining. 25 Another method aspect of the invention proposes the method of increasing the water holding capacity of the soil by having a water container in the ground under the plant such the soil is saturated and such that water can wick up to the roots of the plants and the container may be filled by a pipe directing water to the bottom of the container so is fills from underneath and excess water may be drained away from the container so only 30 saturating a portion of the soil profile. The water may be drained from the saturated layer beneath one plant to supply the soil -8 beneath a second plant by gravity. The depth of the saturated layer may be adjusted by varying the depth of the drain. The drain carrying water to the lower level may be opened or closed to allow temporary 5 saturation of the fill soil depth followed by drainage to the desired level. In this way a soil flush is possible followed by ingress of air to the drying soil. Once a saturated layer beneath the plant is established, water will wick up to the roots above. 10 In many areas there is insufficient irrigation water. The wicking bed system can be modified to capture and amplify rainfall by simply adding wings or extension to the wicking bed to capture water. If for example the area of the wings is equal to the area of the bed, this effectively doubles the rainfall. 15 The amplification is much greater than this as small rains landing on soil only wet the surface and the water will quickly evaporate. The wings are made from an impervious material such as plastic sheet covered with stones. The water is not absorbed but instead flows down to the base of the water reservoir where it is protected. This makes use of 20 small rains and dew otherwise wasted and is an important part of water harvesting. BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention is now described with reference to the accompanying 25 drawings, in which: Figure 1 shows a cascade system for rows of vegetables. Figures 2a-2d shows the stages of construction of a wicking bed. 30 Figure 3 is a diagrammatic section through a raised bed on a wicking bed.

-9 Figure 4 is an exploded view of an aboveground box with a pervious bag and a waterproof liner inside the bag. Figure 5 is a section of a wicking bed with margins for rain capture. 5 DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS A soil bank is cut into terraces 2 which are drained by trench 4. Plastic containers 6, 8, 10 are laid next to the terrace step to stabilise the bank and filled with soil 12. Water 10 supply pipe 14 trickles into container 10, saturates the layer shown before it drains through drain pipe 16 to container 8. In turn container 8 drains into container 6. Valves 18, 20, 22 allow the operator to saturate the full depth of any of the containers. Referring now to Figures 2a-2d, an in-ground bed is prepared as shown. The size of the 15 bed is fixed by excavating a trench 30 1500w x 30001 x 400d in the garden site. A sheet of black polyethylene sheet is trimmed to fit as a liner 32 in the trench to a height of 300mm. The corners are folded into triangular flaps to create a waterproof pond when the liner fills with rain. A 4.5mm length of ag pipe 34 is placed diagonally along the trench with the ends upstanding as shown. Alternatively the water reservoir may be 20 formed from a fabricated plastic liner. The lower part of the trench is backfilled with sugar cane waste 36 to a height of 300mm and then a batch of earthworms, their eggs and casts are added. Worm food is provided in the form of kitchen waste and the worms are covered with soil. Water is supplied to 25 the pipe and visible in the pipe. If watering continues until the liner is full, the excess will flow over the edge of the liner and escape into the surrounding ground. 30 If the bed is constructed above ground as a raised bed with blocks or timber, an overflow pipe can be inserted at a suitable height. Figure 3 shows such a composite bed with a worm house 38 on top.

- 10 Figure 4 shows a box for containing a wicking bed in a situation where there is space but perhaps no garden as in a citiscape. A frame 40 is made of tubes and couplings and stood in a sunny position, for example a balcony. 5 A rectangular sheet of shadecloth 42 is folded to form a bag which fits inside the cuboid frame and the edges of the bag are laid over the frame edges and slits 44 are made to receive plastic cable ties 46 which embrace the frame tubes. A plastic liner 48 sits inside the bag but extends to about half the height of the bag. A U-shaped plastic water pipe 50 with water release holes 52 is inserted diagonally across the liner so as to be supported 10 by the frame. The liner is filled with the coarse organic waste and the waste is covered with dry soil. Water is poured into the upstanding leg of the pipe enabling the voids in the waste to be filled. Excess water will spill over the edge of the liner. The soil above the liner will moisten and become suitable as a propagation bed. 15 The top surface will remain dry and evaporation will be minimised. This type of bed is economical in its use of water and as the water level in the liner falls air is drawn into the voids in the waste. The addition of extra water displaces the air and this cycle shows the return of carbon 20 dioxide to the atmosphere while creating conditions for rapid carbon capture through photosynthesis. In use, a variety of fibrous material suffices for the lower layer. They decompose at different rates and need replacement eventually. For this reason it is helpful to protect 25 the liner against perforation by garden tools by covering the floor of the liner with a protective mat such as discarded carpet. The bed consumes less water than a bed watered from the top down. The wicking effect is observable upon inspection and yields are above average. The addition of liquid or solid manures and fertilisers is unimpaired. 30 The benefits are as follows: There is no seepage of water into the sub soil and there is virtually no loss of water by - 11 evaporation from the surface of the soil due to a dry crust forming on the surface which protects the loss of water and organic material from the moist biologically active region below. Therefore less rainfall and irrigation water is wasted when directed straight into the subsurface layer, giving significantly higher production per unit of water. 5 The subsurface water container holds a considerable volume of water, such that irrigation need only be conducted at infrequent intervals. As the water level in the subsurface container can be readily inspected by a small hole or 10 pipe in the ground or readily detected by a water sensor such as a float valve, it is easily determined when the subsurface container needs refilling and so only the exact amount of water is applied to meet the plant needs without the need for sophisticated irrigation scheduling and irrigation automation. 15 As there is no seepage of water into the ground, and there is a biologically active moist subsurface layer, it is particularly suitable for the recycling of waste organic material such as waste or contaminated water (grey and sewage water). As there is a continuous supply of water, it generates ideal moist conditions for the propagation of suitable breeds of worms and microbes and fungi which can process organic waste which is recycled to 20 improve soil quality and capture carbon which would otherwise enter the atmosphere so producing an agricultural system which is removing greenhouse gases from the atmosphere rather than contributing to greenhouse gases in the atmosphere. The moist subsurface layer fed by wicking action is biologically active providing a 25 balance of air, water and nutrients which improves plant productivity. Construction and operation of such beds provide a method whereby waste organic material which may present disposal problems can be recycled for benefit. Wastewater such as sewage which may contain contaminants or pathogens can be more safely used 30 for irrigation as the water can be transported directly to the subsurface and is not in direct contact with the plants.

- 12 The Figure 5 variant of the bed is useful in a semi-arid region where grass germinates after rainfall but subsequently withers and is eaten perhaps by termites. A trench 60 is dug by a tractor and the margins 62 at the sides of the trench are scraped into an incline by surface soil removal. Strips of overlapped plastic sheet 64 are laid over the margins 5 and the inclines are stabilised with stones 66. Finally the margins are covered with the returned soil and the trench is filled to the margin height. The margins drain percolated rain into the trench. Pasture develops in strips 68 and acts as a windbreak. I have found the advantages of the mesh type bed to be: 10 1. Evaporation is reduced. 2. Nutrients are not flushed away as in conventional growing. 15 3. Water content of the soil is increased from normal field capacity by x2 to x3. 4. The coarse organic waste is inexpensive. 5. Provides a method of capturing atmospheric carbon by photosynthesis to produce 20 organic waste which decomposes under semi-anaerobic conditions often underwater such that the organic material decomposes very slowly and is incorporated by micro-biological action particularly fungi and worms into the structure of the soil. 25 6. Provides a mean of beneficially disposing of solid waste organic material. 7. Provides a means of beneficially disposing of contaminated wastewater such as sewage and taking advantage of any nutrients. 30 It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word "comprising" does not exclude the addition of other elements.

- 13 It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.

Claims (15)

1. A method of constructing a bed for growing plants, comprising forming a growing recess, lining the recess at least partially with a water impervious layer 5 to create a water reservoir, at least partially filling the recess by depositing coarse particulate wicking medium on the lining, depositing growing medium on top of or adjacent to the wicking medium, and introducing water into the wicking medium. 10 2. A method as claimed in Claim 1, wherein the recess is a cavity in the ground and the lining is a sheet of flexible material, a layer of compacted clay or a layer with cement mixed with soil or a layer of concrete.

3. A method as claimed in Claim 1, wherein the recess is the interior of a box or a 15 trench.

4. A method as claimed in Claim 1, wherein the recess is the interior of a bag supported by a frame. 20 5. A method as claimed in Claim 2, including placing the growing medium in soil in contact with surrounding soil.

6. A method as claimed in Claim 3 or 4, including avoiding contact between the surrounding soil and the growing medium when it is soil. 25

7. A method as claimed in any one of Claims 1-6, including distributing a pipe in the water reservoir in order to admit water to the wicking medium when required.

8. A method of operating a bed constructed by the method of Claim 1, including the 30 addition of earthworms and organic material containing fungi or soil bacteria to the growing medium. - 15 9. A method as claimed in Claim 8, including planting deep rooted legumes in the growing medium.

10. A method as claimed in Claim 8 or 9, including the addition of water obtained 5 from sewage.

11. A method as claimed in any one of Claims 8-10, including installation of a drain at a level which prevents the growing medium from reaching saturation. 10 12. A method as claimed in any one of Claims 8-11, including restricting the supply of water so as to keep the exposed surface of the growing medium dry in order to minimise evaporation.

13. A method as claimed in any one of Claims 8-12, wherein water is supplied to the 15 reservoir at or near the lowest level thereof in order to minimise stagnation.

14. A method as claimed in any one of Claims 8-13, wherein the water level in the reservoir is periodically replenished to maintain the growing medium in the root zone moist but not saturated. 20

15. A method as claimed in any one of Claims 1-6 including covering the liner with bubble wrap whereby the bubbles contact the wrap and define flow passages for introduced water. 25 16. A wicking bed for growing plants, comprising a waterproof liner deployed underground in soil, forming a water reservoir, a coarse, particulate layer of wicking medium on top of the liner, and a layer of growing medium on top of the wicking medium. 30 17. A wicking bed as claimed in Claim 16, wherein the liner is extended beyond the reservoir as an inclined margin below ground level for draining rainwater into the reservoir. - 16 18. A wicking bed as claimed in Claim 16 or 17, wherein the liner surface is 200 300mm deep for raised beds and 600-800mm deep for subterranean beds.

19. A wicking bed as claimed in any one of Claims 16-18, wherein the bed is 5 extended to form one or more adjacent beds which cascade, whereby the reservoir of the higher bed drains into the reservoir of the lower bed.

20. A wicking bed as claimed in Claim 16, wherein the bed is raised above ground level and the liner is deployed within a porous open topped bag, the liner being 10 at least partially filled with coarse particulate wicking medium, the volume of the bag above the liner being filled with growing medium.

21. A method of constructing a bed for growing plants, comprising forming a growing recess, lining the recess in order to create a water reservoir depositing 15 growing medium on the lining which increases the water content of the medium from field capacity toward saturation.

22. A method of reducing atmospheric carbon by storing organic waste material in a subterranean cavity which is lined to create a water reservoir and immersing the 20 material so that anaerobic or intermittent anaerobic decomposition prolongs carbon capture and prevents rapid conversion to carbon dioxide.