NZ583765A

NZ583765A - Irrigation system and adding carbon dioxide

Info

Publication number: NZ583765A
Application number: NZ583765A
Authority: NZ
Inventors: Robert Lloyd
Original assignee: Windfuel Mills Pty Ltd
Priority date: 2007-08-10
Filing date: 2008-08-08
Publication date: 2011-07-29
Also published as: WO2009021272A1; AU2008286683A1

Abstract

An irrigation system 10g comprising a hollow tube 210, a temperature controller 160 or a temperature adjustor, a carbon dioxide injector 100 or a dosing device, a control unit 40 and one or more carbon dioxide sensors. The tube 20, 210 has a tube wall 220 with pores 250 extending through it. The tube wall 220 defines a tube interior 230 from which water can pass through the tube wall 220 via the pores 250. The temperature controller 160 will control the temperature of the water. If a temperature adjustor is used instead it will adjust the temperature of the water. The carbon dioxide injector 100 will inject a gas containing carbon dioxide into the water before the water passes out of the tube 20, 210. If the dosing device is used instead, it will add a substance capable of releasing carbon dioxide into the water before the water passes out of the tube 20, 210. The control unit 40 will adjust one or more of the following parameters - the temperature of the water, the rate of injecting carbon dioxide into the water and the rate of addition to the water of the substance capable of releasing carbon dioxide and pH of the water. The one or more carbon dioxide sensors are located downstream of the injector or dosing device. The sensors will send a signal relating to carbon dioxide concentration in the water to the control unit.

Description

1 Irrigation system Technical Field The present invention relates to an irrigation system and to a method of using the system.

Background of the Invention Australia is one of the driest continents on earth. The constant pressure on farmers to produce a reliable and cost effective food source for the ever growing communities is straining the farming sector. Australia is currently witnessing a one in one hundred year drought which is nationwide and many farmers are suffering significant hardship as a result. Many farming communities are at crisis point, and new ideas and technologies are needed to ensure generational change for the nation's food bowl. Much of these problems can be alleviated by a more ready or efficient supply of water. Rainfall may provide short term relief, however other water saving technologies are required in order to provide long term strategies for sustainable agricultural production.

There are problems in growing crops and fodder in dry areas due to lack of sufficient water. Thus there is a need for a system capable of supplying the minimum amount of moisture required within the area of the roots of the crop to be grown. It is estimated that the water requirement at the plant roots is only about 6-7% of that required for spray-on flood irrigation, in which water is wasted by evaporation and by irrigating soil that does not have crops growing. A further problem is the nature of the water available in such dry areas and the acidity of the land. Various water supplies are available, such as wells, bores, dams, etc., however the nature of the water is in many cases unsuitable due to saline content or other impurities.

There is therefore a need for an irrigation system which is capable of providing water with reduced wastage, at a quality suitable for irrigation. It would be preferable if such a system could be supplied at low cost, thereby making it available for use in third world countries.

Object of the Invention It is the object of the present invention to at least partially satisfy at least one of the above needs.

Summary of the Invention An irrigation system is described herein. The system comprises a hollow tube, said tube comprising a tube wall having pores extending therethrough, said wall defining a 2 tube interior, whereby water can pass from the tube interior through the tube wall via said pores. The irrigation system may also comprise any one or more of the following in any combination: • a source of water coupled to the tube interior, said source being capable of passing water to said tube interior under pressure, optionally at a constant pressure; • a gas injector for injecting one or more gases into the water prior to said water passing out of the tube and/or a dosing device for adding into the water a substance capable of releasing the one or more gases; • means to control or adjust the pH of the water; • means to control or adjust the temperature of the water; and • a chemical addition system for adding chemicals to the water.

The irrigation may comprise one or more carbon dioxide sensors locatable in soil surrounding the tube of said system. The carbon dioxide sensor(s) may be coupled to a controller for adjusting one or more parameters which affect carbon dioxide concentration in the water. Such parameters include temperature of the water, pH of the water, pressure of the water, rate of injecting carbon dioxide into the water and rate of addition to the water of a substance capable of releasing carbon dioxide gases prior to said water passing out of the tube. Thus for example if in use the carbon dioxide sensor indicates that there is insufficient carbon dioxide in the soil for efficient growth of a crop, the temperature of the water may be reduced so as to increase the solubility of carbon dioxide in the water so as to allow more carbon dioxide to be present in the water, or the pH of the water may be increased so as to allow more carbon dioxide to dissolve in the water, or the addition rate of either carbon dioxide itself or a carbon dioxide releasing substance may be increased so as to supply more carbon dioxide to the water, or more than one of these steps may be taken in conjunction.

The means to control or adjust the pH may comprise a pH controller for controlling the pH of the water to a desired pH. It may comprise a pH adjuster. The means to control or adjust the temperature may comprise a temperature controller for controlling the temperature of the water. It may comprise a temperature adjuster.

The irrigation system may comprise: • a hollow tube comprising a tube wall having pores extending therethrough, said wall defining a tube interior, whereby water can pass from the tube interior through the tube wall via said pores; and 3 • a source of water coupled to the tube interior, said source being capable of passing water to said tube interior under pressure, optionally at a constant pressure.

The irrigation system may comprise: • a hollow tube comprising a porous tube wall having pores extending therethrough, said wall defining a tube interior, whereby water can pass from the tube interior through the tube wall via said pores; • a source of water coupled to the tube interior, said source being capable of passing water to said tube interior under pressure, optionally at a constant pressure; and • a gas injector for injecting one or more gases into the water prior to said water passing out of the tube.

The following options are available for the irrigation system, and any one or more of these options may be used in the irrigation system described above, either individually or in any suitable combination.

The tube may be surrounded by a mulch. The mulch may be at least partially surrounded by a lining. The lining may be either porous or it may be degradable in soil or it may be both porous and degradable in soil. In this context porous may refer to a material having water channels therethrough. It may for example be a mesh, a woven or non-woven material or some other material through which water can pass, or may comprise more than one of these. The lining may be biodegradable. The mulch may comprise an ash.

The one or more gases may comprise carbon dioxide, nitrogen, ammonia or a mixture of any two or more thereof.

The desired pH may be between about 6 and about 8.

The means to control or adjust the temperature may be capable of controlling the temperature of water to a temperature suitable, or conducive, for growing a crop.

The irrigation system may be adapted to being located in soil.

The irrigation system may comprise: • a hollow tube comprising a porous tube wall having pores extending therethrough, said wall defining a tube interior, whereby water can pass from the tube interior through the tube wall via said pores; • a source of water coupled to the tube interior, said source being capable of passing water to said tube interior under pressure, optionally at a constant pressure; and • a dosing device for adding into the water prior to said water passing out of the tube a substance capable of releasing one or more gases. 4 The irrigation system may comprise: • a hollow tube comprising a porous tube wall having pores extending therethrough, said wall defining a tube interior, whereby water can pass from the tube interior through the tube wall via said pores, said tube being surrounded by a mulch; • a source of water coupled to the tube interior, said source being capable of passing water to said tube interior under pressure, optionally at a constant pressure; • a gas injector for injecting carbon dioxide, nitrogen, ammonia or a mixture of any two or more thereof into the water prior to said water passing out of the tube; and • a pH controller for controlling the pH of the water to between about 6 and about 8; wherein the tube is adapted to being located in soil.

A method for irrigating soil is also described herein. The method comprises: • providing an irrigation system as described above, wherein the tube is at least partially buried in the soil, and • passing the water to the tube interior under pressure, optionally at a constant pressure, such that the water passes out of the tube through the tube wall via the pores thereof and passes into the soil.

The method may additionally comprise the step of injecting one or more gases into the water prior to said water passing out of the tube. Alternatively or additionally it may comprise adding to the water a substance capable of releasing one or more gases. The one or more gases may comprise carbon dioxide, nitrogen, ammonia or a mixture of any two or more thereof.

The method may comprise controlling or adjusting the pH of the water. It may comprise controlling or adjusting the temperature of the water. It may comprise adding one or more chemicals to the water. The chemicals may include one or more of a fertiliser, a nutrient, a trace mineral, a pesticide and a weedicide, and may comprise other suitable chemicals, or a combination of any two or more of the above.

The soil may have a crop therein. In this case the tube may be located in the soil beneath the crop.

A method of growing a crop is also described. The method comprises: • providing an irrigation system as described above; • burying the tube of the irrigation system in soil; • planting the crop in the soil above the tube; and • passing the water to the tube interior under pressure, optionally under a constant pressure; such that the water passes out of the tube through the tube wall via the pores thereof and passes into the soil, thereby irrigating the crop.

The method may additionally comprise the step of injecting one or more gases into water using the gas injector prior to the water passing out of the tube. Alternatively or additionally it may comprise adding to the water a substance capable of releasing one or more gases, using the dosing device.

The following options are available for the method of growing the crop, and any one or more of these options may be used in said method either individually or in any suitable combination.

The method may enable harvesting the crop more than once per year. It may enable harvesting the crop 2, 3 or 4 times per year. It may enable harvesting the crop more frequently than would be the case in the absence of the irrigation system of the present invention.

The irrigation system may comprise means to control or adjust the pH of the water, e.g. a pH controller, and the method may comprise the additional step of adjusting the pH of the water, or of controlling the pH of the water to a pH suitable for growing the crop. This additional step may be conducted before injecting the gas(es) and/or adding the substance capable of releasing one or more gases or may be conducted after injecting the gas(es) and/or adding said substance.

The irrigation system may comprise means for controlling or adjusting the temperature of the water, e.g. a temperature controller or a temperature adjuster, and the method may then comprise the additional step of adjusting the temperature of the water, or of controlling the temperature of the water to a temperature suitable for growing the crop. The controlling or the adjusting may comprise heating and/or cooling the water.

A crop when grown by the method described above is also described.

Brief Description of the Drawings The present invention will now be described in detail with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic illustration of different tube configurations for use in the irrigation system described herein; and Figure 2 is a diagram showing a cross-section of a portion of an irrigation system in use. 6 Detailed Description of the Invention The technology described herein provides farmers with the ability to improve farm production by more efficient use of water. Various forms of the invention provide one or more of the following benefits: • reduced water losses; • improved soil structure and quality; • year-round crop growth; • improved crop reliability; • improved income and assets for farmers; and • utilisation of waste gases from coal burning.

The system of the present invention may be capable of growing crops using as little as about 6% of the quantity of water used by conventional irrigation systems. The system will commonly use about 5 to about 50% of the water used by conventional irrigation systems, or 5 to 20, 5 to 10 or 10 to 50%, e.g. about 5, 6, 7, 8, 9, 10, 20, 30, 40 or 50% thereof. Alternatively it may use similar quantities of water but provide greater productivity from the crops. In some instances it will use less water and provide greater productivity.

The present invention relates to an irrigation system comprising a hollow tube having a tube wall defining a tube interior. The tube wall has pores so as to allow water to pass out of the tube therethrough. In the context of the present specification, "water" should be understood to refer to any aqueous liquid which may be used for irrigating a crop. It may, in addition to the water, comprise one or more other materials such as pH adjusting components (acids, bases, buffers), nutrients, fertilisers, pesticides, weedicides, trace elements and other substances required or preferred by a plant for healthy growth. The water may therefore be an aqueous solution and/or emulsion and/or microemulsion.

The tube may be rigid, or it may be flexible, or it may have rigid portions and flexible portions. It may be a hose or a pipe. It may have an annular cross-section. The outer cross-section and the inner cross-section may, independently, be a circle, an oval, an ellipse, a square, a pentagon, a triangle, a polygon having between 3 and 20 (or between 6 and 20, 10 and 20 or 6 and 12) sides, or may be any other suitable shape. The tube is such that water can pass from the tube interior through the tube wall. The tube wall may be porous. It may be foraminous. It may comprise an open celled foam (in which the pores of the wall represent flow channels through the foam) or it may comprise a plurality of discrete pores or holes leading through the tube wall so as to allow water to pass 7 therethrough. The pores or holes may be distributed along the length of the tube. They may be distributed evenly along the length of the tube. They may be distributed evenly around the circumference of the tube. They may be distributed unevenly around the circumference of the tube such that water comes preferentially out of one side of the tube, for example the side that is uppermost when the tube is buried in soil. They may be distributed unevenly along the length of the tube.

At least some, optionally all, of the pores or holes may communicate with side tubes. The side tubes may be of sufficient length that, in use, they extend above the surface of the soil in which the tube is located, so that water exiting the pores coupled to the side tubes exits said side tubes above the surface of the soil. They may extend between about 0.1 and about 2m above the soil or more than 2m, depending on the nature of the plants growing in the soil. This may enable a portion of the water provided by the system to be provided to the soil from above, or to leaves of plants growing therein directly. It may also allow another portion of the water to be provided below the surface of the soil (e.g. directly through the walls of the tube). In some embodiments the tubes extend above the leaves of the plants so that water exiting the tubes falls on the upper surfaces of the leaves. In other embodiments the tubes do not extend above the leaves. This enables the water to irrigate the soil. In the event that side tubes are present, they may be spaced about 0.2 to 2m apart, or about 0.2 to 1, 0.2 to 0.5, 0.5 to 2 or 1 to 2m apart, e.g. about 0.2, 0.3, 0.4, 0.5, 1, 1.5 or 2m apart. They may be distributed along the tube so that each plant growing in the soil in which the pipe is located, in use, has at least one side tube associated therewith. The side tubes may, for example, have an internal diameter of about 5 to about 20mm, or about 5 to 10 or 10 to 20mm, e.g. about 5, 10, 15 or 20mm. The side tubes may be porous or may be non-porous. They may be open ended or, in the event that they are porous, may be closed ended. Side tubes with holes along their length may enable water exiting the tubes to both irrigate the soil and moisten the leaves of the plants.

The tube may have an outside diameter of between about 1 and about 20cm, or between about 1 and 10, 1 and 5, 1 and 2, 2 and 20, 5 and 20, 10 and 20, 2 and 10, 2 and 5 or 5 and 10cm, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20cm. It may have an inside diameter of between about 0.5 and about 19.5cm, provided that the inside diameter is smaller than the outside diameter. It may have an inside diameter of between about 0.5 and 18, 0.5 and 15, 0.5 and 10, 0.5 and 5, 0.5 and 2, 0.5 and 1, 1 and 19.5, 2 and 19.5, 5 and 19.5, 10 and 19.5, 1 and 10, 1 and 5, 1 and 2, 2 and 5 8 or 5 and 10cm, e.g. about 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 19.5cm. The wall thickness of the tube should be sufficient to withstand the pressures applied to it, and will depend on the nature of the material from which it is fabricated. It may be between about 0.1 and about 5cm, or between about 0.1 and 2, 0.1 and 1, 0.1 and 0.5, 0.1 and 0.2, 0.5 and 5, 1 and 5, 2 and 5, 0.2 and 5, 0.2 and 1, 0.2 and 0.5, 0.5 and 5, 0.5 and 2, 0.5 and 1, 1 and 5, 2 and 5 or 1 and 2cm, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5cm. It is preferable that the wall thickness is minimised, consistent with the tube having the required strength (i.e. crush resistance and burst resistance). The tube may have a porosity between about 1 and about 60%, depending in part on the nature of the pores and on the nature of the material from which the tube is made. The porosity may be between about 1 and 50, 1 and 20, 1 and 10, 10 and 60, 20 and 60, 10 and 50, 10 and 30 or 30 and 50%, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60%. The pore size may be sufficient to permit the desired flow of water through the tube wall at the pressure used. The mean pore size may be between about 0.01 and about 2mm or more, or between about 0.05 and 2, 0.1 and 2, 0.2 and 2, 0.5 and 2, 1 and 2, 0.01 and 0.5, 0.01 and 0.1, 0.01 and 0.05, 0.1 and 0.5, 0.1 and 0.2 or 0.2 and 0.5mm, e.g. about 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2mm. The pores maybe in the form of a network of holes (as for example in an open cell foam), or may comprise discrete pores or holes between the outside and inside of the tube (optionally radially therebetween). In some cases the pores or holes may be larger than 2mm in diameter, e.g. 3, 4, 5, 6, 7, 8, 9 or 10mm in diameter. In some instances the pressure may vary along the length of the tube. In this case, there may be a variation in pore size along the length of the tube to compensate for the pressure drop, i.e. in areas of the tube with relatively low pressure, the pore size may be relatively large so as to achieve a relatively constant flow rate out of the tube along its length. It may in some instances be useful to provide a fine filter outside the tube in order to prevent particles from the soil, mulch etc. from entering or clogging the pores of the tube. This may be particularly beneficial in the event that the mean pore size is about the same size or larger than the mean particle size of the surrounding material (soil, mulch etc.). The fine filter, if present, may have a pore size of less than about 500 microns, or less than about 200, 100, 50, 20 or 10 microns, or of about 10 to about 500 microns, or about 10 to 200, 10 to 100, 10 to 50, 50 to 500, 100 to 500, 200 to 500, 50 to 200, 50 to 100 or 100 to 200 microns, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450 or 500 microns. 9 The length and other dimensions of the tube will depend on the nature of the crop to be irrigated and the area of soil to be irrigated. Thus a crop having plants which are large and/or require a large quantity of water, may require a longer and/or larger diameter tube. The tube may be for example between about 1 and about 100m long, or between about 1 and 50, 1 and 20, 1 and 10, 1 and 5, 5 and 100, 10 and 100, 20 and 100, 50 and 100, 10 and 50,10 and 20 or 20 and 50m long, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100m long, or may be longer, e.g. about 150, 200, 250, 300, 350, 400, 450 or 500m long. The tube may be made from any suitable material that has the required strength and chemical/biological resistance. Thus it should be made of a material that will not burst or crush under the forces applied to it in use. This will of course also depend on the dimensions of the tube. It should not be biodegradable or otherwise degradable in the conditions of use. It may for example be made of a metal (e.g. steel, aluminium etc.), a plastic (e.g. polypropylene, polyethylene, polymethylpentene, polyvinylchloride, polyamide such as polyamide-6, -6,6, -5,7, -11 etc.), a rubber (e.g. natural rubber, polyurethane rubber, polybutadiene, styrene-butadiene rubber), a ceramic or of some other suitable material. It may comprise a combination of such materials. It may have portions that are made of different materials, e.g. different metals, different plastics or some portions plastic and some portions metal. The pores of the tube may have hydrophilic walls, to facilitate the passage of water therethrough.

The irrigation system also may also comprise one or both of: • a source of water coupled to the tube interior, said source being capable of passing water to said tube interior under pressure, optionally at a constant pressure; and • a gas injector for injecting one or more gases into the water prior to said water passing out of the tube and/or a dosing device for adding into the water a substance capable of releasing one or more gases.

The source of water may comprise a pressure regulator for ensuring that the water is supplied to the tube interior under pressure, optionally at a constant pressure. It should be noted that the constant pressure refers to the pressure at the point where the water enters the tube. Due to frictional losses and other losses, there will generally be pressure variation, commonly pressure drop, along the length of the tube. The source of water may comprise a pump, e.g. a pump capable of providing a constant output pressure. It may comprise a reservoir at a fixed height above the tube. The reservoir may have a level switch (e.g. a ball valve) to ensure that the water level therein is constant, and thus that a constant pressure of water is supplied to the tube. The required height of the reservoir may be readily calculated from the desired pressure in the tube from the formula: height (in metres) = pressure (in kg/m ) x 10" A suitable pump for use in the source of water may be a windmill, or a solar powered pump, or some other pump powered by renewable energy, or by energy that is not obtained from an electricity grid. This feature may make the irrigation suitable for use in remote areas where electricity from a power grid is irregular, unreliable or unavailable. Alternatively the pump may be connected to the electricity grid. The source of water may be coupled to one end of the tube. In this instance the other end (the distal end) of the tube may be blocked or sealed, to ensure that the water in the tube interior passes through the tube wall in use. Alternatively the source of water may be coupled to both ends of the tube. The source of water should be capable of delivering water to the tube interior at a sufficient pressure that the desired flow of water through the tube wall may be maintained when the tube is buried in the soil. The irrigation system may comprise one or more moisture sensors (locatable in soil) for sensing the moisture content of soil surrounding the tube. The system may also comprise a feedback system from said sensor(s) to the pressure regulator so that, in use, the pressure regulator can adjust the pressure to ensure a desired moisture content of the soil. The pressure will depend on several factors including the desired flow and the pore size and porosity of the tube wall and optionally on the desired moisture level of soil surrounding the tube in use. When water is supplied to the tube, the pressure along the tube may not be constant along its entire length. The variation in pressure along the tube may be dependent on such factors as the flow rate through the tube wall and the length of the tube. In the event that the flow through the tube wall is low, the pressure may vary only slightly along the length of the tube. A suitable pressure may be between about 1 and about 5 atmospheres, or about 1 to 4, 1 to 3, 1 to 2, 1 to 1.5, 1 to 1.2, 1.5 to 5, 2 to 5, 3 to 5, 1.5 to 4, 1.5 to 3, 1.5 to 2, 2 to 4, 2 to 3, 1 3 to 1.6 or 1.5 to 1.8 atmospheres, e.g. about 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.5, 4, 4.5 or 5 atmospheres, although in some circumstances it may be greater than 5 atmospheres, e.g. 6, 7, 8, 9 or 10 atmospheres.

The distal end of the tube, or tubes, may be fitted with flush valves to allow flushing of the tubes. This may be part of a regular maintenance schedule. The flush valves may be connected to a flush tube which leads above the soil so that any flush water may be collected, and optionally recycled or reused. The flush tubes may in some cases be connected to a flush manifold. Alternatively or additionally the system may comprise a 11 water feed line to collect water from near the crops and feed it to the water source. Thus for example, crops may be planted in such a manner that there are furrows or troughs near the plants. Water may collect in these furrows or troughs, from rain water, hose irrigation or from irrigation using the system of the present invention. The water feed line may take this water and pass it to the water source. It may be fitted with a pump to assist this process. It may be fitted with a water treatment system, for example a filter and/or settling system, for treating (e.g. filtering) the water prior to it entering the water source.

The gas injector may be any suitable injector for injecting gases into the water. The gases may comprise carbon dioxide, nitrogen, ammonia, a mixture of any two or more thereof, or some other gas. In some circumstances it may be beneficial to inject oxygen, and the gas injector may therefore be connected to a source of oxygen for injecting oxygen into the water. The gases may be injected separately through separate injectors, or may be mixed and the resulting mixed gas injected through a single injector. Carbon dioxide is important for promoting the healthy growth of plants, and when passed into the soil in the water used in the present irrigation system, the carbon dioxide can exit the soil under the leaves of the crop plants, and provide a high carbon dioxide environment conducive to improved growth. Certain crops, legumes, also can utilise molecular nitrogen directly in growth. Legumes able to fix atmospheric nitrogen, due to a symbiotic relationship with certain bacteria known as rhizobia found in the root nodules. The ability to form this symbiosis reduces fertilizer costs for farmers and gardeners who grow legumes, and means that legumes can be used in a crop rotation to replenish soil that has been depleted of nitrogen. Thus when growing legumes, it may be advantageous to inject nitrogen into the water, so as to supply nitrogen directly to the roots of the crop rather than relying on diffusion from the atmosphere. The source of the gases to be injected may be any convenient source. It may be from gas cylinders or from gas generators. Carbon dioxide may be obtained by combustion. It may for example be obtained as a waste product from a process that incorporates a combustion step. Certain farming practices require burning of plant material, and in this case the carbon dioxide may be obtained from this burning.

Either instead of or in addition to the gas injector, the irrigation system may comprise a dosing device for injecting into the water a substance capable of releasing one or more gases. The substance may be capable of releasing the one or more gases slowly. It may be capable of releasing the one or more gases over an extended period of time, e.g. over a period of at least about 1 day, or at least 2, 3, 4, 5 or 6 days, or at least about 1, 2, 12 3, 4, 5, 6, 7, 8, 9 or 10 weeks, or over a period of about 1 day to about 10 weeks, or about 1 to 10 weeks, 2 to 10 weeks, 5 to 10 weeks, 1 day to 1 week, 1 to 3 days or 2 days to 2 weeks, e.g. about 1, 2, 3, 4, 5 or 6 days, or at about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 weeks. The substance may have the gas(es) dissolved or otherwise bound therein, so as to be able to release the gases slowly. The substance may be capable of decomposing so as to release the gases. In one example the substance is ammonium carbonate or ammonium bicarbonate. These substances can decompose to form ammonia and carbon dioxide. In this case the ammonia can be slowly released into the soil to act as a fertiliser for the crop, and the carbon dioxide can be released so as to form a high carbon dioxide region in the vicinity of the leaves of the crop so as to promote growth of the crop. Ammonium carbonate and/or ammonium bicarbonate may be added to the water as a solid salt or mixture thereof or as a solution, or by adding both carbon dioxide and ammonia gases to the water, optionally in stoichiometric on near stoichiometric amounts. The ammonia and carbon dioxide may for example be added in a molar (or volume) ratio of between about 1:1 and about 2:1 ammonia to carbon dioxide, or about 1:1 and 1.5:1, 1.5:1 and 2:1 or 1.7:1 and 1.3:1, e.g. about 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1.

The nature of the dosing device for adding the substance will depend on the nature of the substance. For example if the substance is a liquid (e.g. a solution) the dosing device may comprise a pump together with a suitable pipe or other conduit for adding the substance to the water. If the substance is a solid a solid transfer device may be used. Such devices are well known. In use, the dosing device may add the substance to the source of water (e.g. to a reservoir or a tank or other source of water) or may add the substance to the tube. Addition of the substance as a liquid, e.g. a solution, may provide the advantage of easier, more accurately quantitated, addition of the substance to the water. Addition of the substance as a solid may provide the advantage of a slower rate of decomposition prior to addition to the water.

In addition to providing gases through the water, the system of the invention may comprise means to control the atmosphere in which the crop is grown. The means may comprise an enclosure for at least partially surrounding or enclosing the crop. It may for example comprise a greenhouse. It may comprise a gas supply line. The gas supply line may be disposed so as to supply gas to the interior of the enclosure. The gas may comprise for example carbon dioxide and/or nitrogen, or may comprise air supplemented with one or both of these. The means to control the atmosphere may comprise a plurality 13 of such lines. In some embodiments, a supply line is provided to each of the plants of the crop so as to provide a controlled atmosphere to said plants. The supply line may open near the foliage of the plants. The flow rate of the gas through the supply line may be sufficient to control the atmosphere in the vicinity of the plants sufficiently to promote or improve growth of the plants. It will be understood that this flow rate will depend on the nature of the plants, the composition of the gas, the number of plants, the configuration of the supply line(s), the proximity of the supply line(s) to the plants, the size of the enclosure (if present) etc. The system may comprise means to control the temperature of the atmosphere surrounding the plants. This may comprise a temperature adjuster and/or controller fitted to the supply line so that gas supplied therethrough is at a suitable temperature, or it may comprise some other form of temperature controller/adjuster. The enclosure, if present, may itself serve as a temperature controller/adjuster by preventing loss of heat from the plants, and/or by restricting air movement (e.g. wind) in the vicinity of the plants. Other temperature adjusters/controllers such as radiators may be used.

The irrigation system of the present invention may additionally comprise any one, two, three, four or five of the following features or may comprise all of the following features: a filter - this may prevent fine material from the water source, or generated by addition of one or more substances to the water from the source, from fouling the pores of the tube. Natural waters may comprise fine particulate material, and precipitates may form for example by precipitation of salts of low water solubility. These may progressively foul the pores of the tube of the present system. They may be at least partially removed, thereby preventing or slowing the fouling, by filtration of the water prior to it entering the tubes. The location of the filter may be dependent in part on the nature of the fouling. For example if fine particulates are present in the source water, it may be preferable to locate the filter immediately after the exit from the source. If the particulates are due to precipitation caused by addition of substances to the water, it may be preferable to locate the filter as far downstream from the addition point as possible (providing that it is upstream of the pores of the tube) to allow time for the precipitate to form and if possible aggregate. There may be filters in both these locations, or either location. Suitable filters include media filters, membrane filters, sand filters etc. The filter may be a backflushable filter, in order to reduce the fouling of the filter in use. Backflushing of the filter, or other suitable cleaning (e.g. chemical cleaning) may be part of a regular maintenance schedule for the system. 14 a flush system - this may be used to clean the system once some degree of fouling of the pores has occurred. The flush system may comprise a series of valves, and optionally bypass tubes, in order to allow for a high flow through the tubes. This high flow may be used to sweep the internal surface of the tube(s) of the system in order to remove deposited matter and reduce fouling. The flush system may comprise flush valves at the distal end of the tube, or tubes. The, or each, flush valve may be connected to a flush tube which leads above the soil so that any flush water may be collected, and optionally recycled or reused. The flush tubes may in some cases be connected to a flush manifold. In some cases it may be beneficial to add cleaning or defouling agents to the flush water in order to assist in removing foulants. These may comprise antimicrobial agents, e.g. chlorine, iodine etc. and/or chemical agents such as acids, chelators etc. for removing non-biological fouling agents. The system may therefore also comprise a dosing pump for adding the cleaning agents and/or defouling agents to the flush water and a cleaning/defouling agent reservoir for supplying the cleaning/defouling agent to the dosing pump. a backflow preventer - this may be provided to prevent water from the system returning to the water source. In some instances the water source may provide water for other uses than irrigation. If water is permitted to return to the source, it may add substances (e.g. fertilisers) to the source that make it unsuitable for the other uses, e.g. for drinking, or may lead for example to algal growth in the water source. The backflow preventer may comprise an antisiphon valve. It may comprise a one-way valve, e.g. a leaf valve, a ball check valve, a swing check valve or some other type. It may comprise a check valve. It may comprise a double check valve. The backflow preventer may be located near the exit from the water source. It may suitably located between the water source and the first point in the system at which a substance is added to the water. a water treatment system - the water in the water source may contain substances which impair the operation of the system. For example the water may comprise high levels of calcium and/or magnesium. These are commonly found in ground water sources, and can interact with additives to the water (e.g. with carbon dioxide) to produce insoluble carbonates, which can precipitate and form scale in the tube. The scale can partially block the pores of the tube and thereby reduce the flow rate of water through the wall of the tube. High levels of iron can similarly result in precipitates forming in the tube and fouling the pores. Additionally, the water may comprise particulate matter, e.g. colloidal matter, that can foul the tubes. It may also comprise microorganisms that can form biofilms in the tubes and thereby foul the pores. As noted above, foulants may be at least partially removed by flushing, particularly with appropriate chemical agents for removing the foulants, however pre-treatment of the water can reduce the rate of fouling and thereby reduce the required frequency of flushing. The water treatment system may comprise a filter, a prefilter, a microfilter, an ultrafilter, a reverse osmosis unit, a deioniser, a softener, an ion exchanger, a settler or a combination of any two or more of the above. Alternatively or additionally it may comprise a steriliser for killing or removing microorganisms in the water. This may prevent or inhibit fouling of the pores of the tube, and may also prevent or inhibit exposure of the plants irrigated by the system to harmful microorganisms that could cause plant disease. The steriliser may be in the form of a filter, a microfilter, an ozoniser, a radiation (e.g. UV) steriliser or some combination thereof. control system — any or all of the valves and/or pumps of the system may be remotely controllable valves and/or pumps, e.g. solenoid valves may be used, so that they can be controlled by a control system. The control system may comprise one or more sensors to determine various parameters in the system. For example the sensors may determine flow rate, pressure, temperature, etc. in the system. There may additionally or alternatively be sensors in the soil surrounding the tube, optionally near the roots of the plants. These may detect levels of carbon dioxide, nitrogen and/or moisture and various nutrients such as potassium, phosphorous in the soil. The sensors may be coupled to a control unit, e.g. a computer or PLC (programmable logic controller) so as to provide a signal to the controller relating to the parameter detected. That signal may be used by the processing unit to control electrically controllable valves such as solenoid valves so as to control the composition and/or flow rate of the water so as to optimise the growing conditions for the plants irrigated by the system. For example, one sensor may measure moisture level near the roots of the plant. When the moisture level drops below a predetermined level, the sensor relays this to the controller, which sends a signal to valves controlling the flow of water to the tube in order to increase the water flow rate. Another sensor may measure the temperature of the soil near the roots of the plant. When the temperature is outside a predetermined range, the sensor would signal the controller, which would control a temperature controller to correct the water temperature. In a further example, a pressure sensor in the system may determine when pressure exceeds a predetermined threshold. This may signal the controller to institute a flushing routine (e.g. opening flush valves, adding chlorine to the water, adjusting the pH of the water to acidic) 16 in order to flush the tube and remove fouling. Another sensor may measure flow rate. If the flow rate increases this may signal a leak in the tube, and an alert may be sent to an operator that maintenance is required. The system may additionally comprise a rain sensor, so that the system provides water at a lower rate, optionally stops providing water, when it is raining, so that water is not wasted in being provided through the system when it is available through rain. The control system may be capable of controlling the timing of addition of substances (gases, other chemicals, pH control chemicals) to the water and/or the temperature control/adjustment. It may therefore comprise a timer. It may control these independently. It may control them so that the substances are each added at a time that they are required by the plants and are not added at a time when they are not required by the plants. For example carbon dioxide, which is used in photosynthesis, may not be required at night, and therefore the controller may control the system so that carbon dioxide is not supplied at times of low light. It may be capable of controlling on a regular on-off regime. It may be capable of regulating the level of addition on a regular basis. a chemical addition system - apart from pH control and addition of gases, it may be advantageous to add other chemicals to the water in order to improve growing conditions for the crop being irrigated. Suitable chemicals include fertilisers, nutrients, trace minerals, pesticides, weedicides etc. The addition of these through the present system enables them to be delivered directly to the roots of the plants. This has the benefit that they are made available where they are needed, and may also reduce the consumption of these chemicals. This may represent a cost saving to the farmer, and also reduce pollution due to escape of these chemicals into the broader environment. It may also restrict the growth of weeds by restricting the area over which these beneficial chemicals are available. The chemical addition system may comprise suitable tanks, valves, pipes etc. to dose the chemical(s) into the water. It may also comprise one or more sensors to determine the levels of the chemicals in the soil and/or in the water. The sensor(s) may be coupled to a controller which is capable of controlling the dosing rate of the chemicals. The chemical addition system may be capable of supplying the chemicals to the water at a variable rate so that the chemicals are added only as needed, or according to a predetermined schedule.

In an irrigation system according to the present invention, there may be one tube, or there may be two or more tubes. There may be between 1 and 500 tubes or more than 500 tubes. There may be between 1 and 200, 1 and 100, 1 and 50, 1 and 20, 1 and 10, 10 and 17 500, 50 and 500, 100 and 500, 10 and 200, 10 and 100, 10 and 50, 10 and 20, 50 and 200 or 100 and 200, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90,100, 150, 200, 250, 300, 350, 400, 450 or 500 tubes. If more than one tube is used, these may be manifolded, using one or more manifold (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 manifolds). This may be useful in cases where a field has multiple rows of crops to be irrigated by the irrigation system. Thus the tubes may be coupled to the source of water via a manifold. In this event, there may be one or more gas injectors in the manifold, so that the gas passes into the water before it enters the tubes. Alternatively or additionally there may be separate injectors in one or more of the tubes. This may be particularly useful if the different tubes are to be used to irrigate different crops which have requirements for different gases, or for different concentrations of gases. In an alternative, one long tube may be used and may be shaped so as to provide irrigation to multiple rows of crops.

Some tube configurations are shown in Fig. 1, although it will be readily appreciated that other configurations are also possible, and are envisaged by the present inventor. In Fig. 1, irrigation systems 10a, 10b, 10c, lOd, lOe, lOf, lOg and lOh comprise one or more hollow tubes 20. Each tube 20 comprises a tube wall having pores (not shown) extending therethrough, said wall defining a tube interior, as illustrated in Fig. 2. The tubes 20 are buried in the soil, below crop plants 30, as also shown in Fig. 2. Commonly crop plants 30 are sown in rows, and these will be arranged so that each plant is above a portion of a tube 20. The irrigation systems also comprise a source of water 40 coupled to the interior of tube(s) 20. Source 40 is capable of providing water to tube(s) 20 at a constant pressure, which pressure is sufficient for the water to pass through the tube wall via the pores thereof and into the soil. Source 40 may for example comprise a windmill, or some other pump, designed to maintain a constant pressure to tube(s) 20. Systems 10a to lOh all have gas injectors for injecting one or more gases into the water, although these are not shown in systems 10a to 10c for reasons of simplicity.

With reference to the individual configurations of Fig. 1, system 10a shows a single tube 20 coupled to source 40, and sealed at end 50 distal to source 40. Tube 20 follows a first row 60 of crop plants, then bends to return along a second row 70 of crop plants, continuing down the remaining rows of plants. In use, water from source 40 passes into tube 20 and penetrates through the tube wall along the length thereof, thereby irrigating plants 30. System 10b is similar to system 10a, however tube 20 initially passes around 18 the perimeter of the group of crop plants 30 and then progresses further towards the centre of the group of plants in a rectangular spiral-like fashion as shown.

System 10c is a manifolded system. Thus in system 10c, tubes 20 are connected at one end to manifold 80, which couples tubes 20 to source 40 via manifold feed line 90. Each of tubes 20 of system 10c are sealed at end 50 distal to manifold 80. Each tube 20 passes below a row of crops 30. In use, water provided by source 40 passes though feed line 90 into manifold 80. Manifold 80 feeds water to tubes 50 roughly evenly, and the water penetrates through the walls of tubes 20 along the length thereof, thereby irrigating plants 30. In some embodiments of the invention, manifold 80 and/or tubes 20 may be designed so that the flow into different tubes 20 is different. This has the effect that plants 30 above some tubes 20 receive different water flows to plants 30 above other tubes 20. This may be desirable if the irrigation system is used for irrigating different types of crops. For example certain farming practices require alternation of rows of two different crops. In this case, if the different crops have different water flow requirements, the manifold (e.g. the bore of the connections to tubes 20) may be adjusted, or the nature (e.g. porosity, pore size, wall thickness, internal diameter etc. of the tubes may be adjusted) to ensure that each tube provides the water flow that is appropriate for the crop growing above it. In Fig. 10c, tubes 20 are shown as straight, however it will be understood that these may in practice be any convenient shape. For example they may be curved in order to follow the contours of a hill.

System lOd is a manifolded system similar to that described above and shown in Fig. 10c. System lOd, in addition to the components described for Fig. 10c, comprises gas injector 100, connected to gas source 110 by gas line 120. It also comprises pH controller 130, connected to pH control solution reservoir 140 by line 150. It also comprises temperature controller 160. The operation of system lOd is similar to that of system 10c. Prior to water from water source 40 entering manifold 80, it is pH adjusted by means of pH controller 130. Thus a pH control solution contained in reservoir 140 passes through line 150 and is dosed into the water by means of a dosing device at a rate suitable to achieve the desired pH. The pH control solution may be a base, an alkali or a suitable buffer. Controller 130 may comprise a pH probe, which determines the pH of the pH adjusted water to provide feedback in order to control the dosing device to achieve the desired pH. After pH adjustment, the water passes to temperature controller 160, which adjusts the temperature of the water to a desirable temperature for growing plants 30 (allowing for temperature changes which may occur through manifold 80 and tubes 20). 19 Controller 160 may be a heater, or may be a cooler, or may comprise both a heater and a cooler to accommodate variations either side of that desired in water source 40. Following temperature adjustment, suitable gases, commonly carbon dioxide and/or nitrogen and/or ammonia, are injected into the water from source 110 through line 120, by means of injector 100. Commonly injector 100 will comprise a means for injecting the gas into the liquid, e.g. a sparge, as well as a means to agitate the liquid to ensure good dissolution of the gas into the water. This may for example comprise baffles to encourage turbulent flow of the water. In this manner, water of the desired pH, temperature and gas concentration is fed to manifold 80 and passes to plants 30. It will be understood that temperature controller 160 may be located before or after either injector 100 or controller 130. Commonly pH adjustment will be conducted before gas injection. In this way, when carbon dioxide is fed to the water it will become more acidic. When this acidic water is passed into the soil, the carbon dioxide will pass up through the soil to the plants, leaving the water at the desired adjusted pH.

System lOe is also similar to system 10c, however in this system gas injectors 100, temperature controllers 160 and pH controllers 100 have been fitted individually to each line 20. The operation of these is as described for system lOd. However in system lOe it is possible to provide different growing conditions, suitable to different crops, for each line 20, since adjustment is conducted after the water has left manifold 80. This may be desirable in cases in which different crops are to be irrigated by the same irrigation system.

System lOf, as with system lOd, comprises gas injector 100 connected to gas source 110 by gas line 120. It also comprises pH controller 130 connected to pH control solution reservoir 140 by line 150 and temperature controller 160. Additionally system 1 Of has chemical addition injector 200 for adding a liquid chemical to the water and which is connected to chemical reservoir 210 by line 220. Feed line 90 connects source 40 to inlet manifold line 80, which is closed at distal end 50. Tubes 20 are in the form of side lines from manifold line 80, each of tubes 20 passing under one of plants 30. Tube 20 may be coiled or otherwise disposed so as to increase the length of tube 20 that is underneath each plant 30, so as to enable higher water flow under the plant where it is needed, if this is required. The distal ends of tubes 20 are connected to outlet manifold line 240, and each line 20 has a check valve 230. Manifold line 240 can output in the direction of arrow 250, and may, if desired, be connected back to source 40 so as to recycle water from manifold line 240. Thus in use, water from source 40 passes through line 90. As it does so, pH controller 130 adjusts the pH of the water to the desired pH using pH control solution from reservoir 140, temperature controller 160 adjusts the temperature of the water to the desired temperature, and gas injector 100 injects gas from gas source 110, as described previously. Additionally, chemical addition injector 200 adds liquid chemicals (which may be solutions of active chemicals) from reservoir 210 as required. These may be for example fertilisers or other soluble nutrients required by plants 30 for healthy growth, and should be miscible with water. The addition may be in some cases intermittent, or it may be continuous, as required by the nature of plants 30 and the prevailing conditions. The water at this stage is suitable for delivery to plants 30, and passes from inlet manifold line into tubes 20, where it can pass through the walls of tubes 20 underneath plants 30 to encourage growth thereof. Under normal operation, check valves 230 are closed, so that water entering the system from source 40 is all delivered through tubes 20 to surrounding soil. However if partial blockage is detected, or as a matter of routine maintenance, check valves 230 may be opened and a high flow passed through tubes 20 in order to flush out foulants etc. The flush water then passes through valves 230 into outlet manifold 240. It may be discarded, or may be returned to source 40, preferably after suitable treatment to remove foulants etc.

System lOg, as with system lOd, comprises gas injector 100 connected to gas source 110 by gas line 120. It also comprises pH controller 130 connected to pH control solution reservoir 140 by line 150 and temperature controller 160. In system lOg, feed line 90 connects to manifold line 80 and is fitted with gas injector 100, pH controller 130 and temperature controller 160. It is also fitted with filter 260 for removing solid matter from the water which might otherwise foul the pores of tubes 20. Tubes 20 are in the form of side lines from manifold 80, and project upwards therefrom. They are closed at their distal ends so as to force water out of the pores in the walls thereof. Manifold 80 is also blocked at its distal end 50 for similar reasons. System lOg is suitable for use with plants in pots 280, which can be placed over tubes 20 when required such that tubes 20 penetrate into the soil in pots 280. Tubes 20 may be connected to manifold 80 by non-porous connectors 270 if desired, so that all water is directed into pots 280. Pots 280 (with plants 30 therein) may be easily removed and replaced by other pots as desired. This may be particularly suitable for use in a plant nursery for example. Thus in use, water from source 40 passes through line 90 and is adjusted to an appropriate pH and temperature using pH controller 130 and temperature controller 160. Suitable gases, e.g. carbon dioxide and nitrogen, are added through gas injector 100. Any solid matter is removed by filter 260, 21 which may be for example a sand filter, or a microfilter, before entering manifold 80. The water then passes from manifold 80 through connectors 270 and into porous tubes 20, from where it passes into the soil in pots 280 and is provided to plants 30.

System lOh comprises gas injector 100, connected to gas source 110 by gas line 120. It also comprises pH controller 130, connected to pH control solution reservoir 140 by line 150, and temperature controller 160. Additionally system lOh has chemical addition injector 200, which is connected to chemical reservoir 210 by line 220. Line 90, which leads from source 40 to line 20, is fitted with non-return valve 290 to prevent water that has been dosed with various chemicals (e.g. pH adjusters, fertiliser etc.) from returning to source 40. Alternatively, source 40 may comprise a pump for passing the water through system lOh, said pump comprising a non-return facility. Downstream of injector 200, detector unit 300 is provided to monitor the condition of the water entering line 20. Unit 300 may for example comprise one or more of a temperature probe (e.g. thermocouple, thermometer), a pH probe, a gas concentration probe and a sensor for chemicals added by injector 200. It may also have probes to detect pressure and/or flow rate through line 90 so as to be able to determine leaks, blockages etc. Unit 300 is connected to controller 310 by line 320, which conveys signals from the probes to controller 310. Controller 310 is capable of monitoring the signals from the probes, and of controlling injectors/controllers 100, 130, 160 and 200 (via control lines 360, 340, 350 and 365 respectively), so as to provide the desired temperature and concentrations of additives to the water. Controller may also be capable of controlling source 40, in particular a pump thereof, by means of control line 330. Filter 260 may also be provided to remove any particulate matter from the water, so as to minimise fouling of tube 20. Commonly filter 260 will be located upstream of unit 300, so as to also protect the probes in unit 300 from fouling. Filter 260 should be located a suitable distance, e.g. at least about 2-3m, downstream of injector 200, so as to allow for thorough mixing, and for formation of precipitates that may form due to combinations of additives in the water, so that these may be removed prior to entering tube 20. At the distal end of tube 20 is check valve 230, which is connected to return line 370 leading to source 40. Line 370 should be provided with filter 380 to remove particulate matter from the water prior to it returning to source 40.

In operation of system lOh, water from source 40 passes into line 90 and is provided with gases, pH control solution and other chemicals (fertiliser etc.), and has its temperature adjusted, by controllers/injectors 130, 160, 100 and 200 (in order of action). 22 Non-return valve 290 prevents water returning these materials to source 40 in case of unwanted pressure fluctuations. The water then passes through filter 260, which removes any residual particulate matter, and thence to detector unit 300. Detector unit 300 provides signals to controller 310 so as to provide feedback control to controllers/injectors 130, 160, 100 and 200 in order to maintain the desired temperature, gas concentration, additive concentration etc. in the water entering tube 20. Importantly unit 300 also measures pressure and flow rate of the water. Increased flow rate and/or reduced pressure may be indicative of a leak in tube 20, which may require maintenance. Thus increased flow rate and/or reduced pressure may be signalled to an operator by an appropriate warning on a panel or monitor of controller 310. Reduced pressure and/or increased flow rate may indicate blockage of the pores of tube 20, and may therefore indicate the need for cleaning. A cleaning regime may be instituted manually, following signalling of the problem in the controller. Alternatively an automatic cleaning regime may be instituted, as described below. In normal operation however, the filtered and dosed water passes to tube 20, where it passes out through the pores to irrigate plants 30. In doing so, it may pass through a mulch layer (note shown, but see Fig. 2) surrounding tube 20, thereby picking up nutrients which can be passed to the roots of plants 20. The irrigation, as described elsewhere, also provides increased carbon dioxide to the leaves of the plants in order to encourage growth. It may also provide fertiliser (from reservoir 210) to the plants. In order to ensure that water exits tube 20 through the pores in the walls thereof, check valve 230 is in a closed position in normal irrigation operation. As noted above, it may be necessary to flush the system in order to remove fouling (either due to precipitates, accumulated particulate material or biofouling, or a combination thereof). This may be scheduled regularly as preventative maintenance or may be in response to an increase in pressure or reduction in flow rate detected by unit 300. The flushing may comprise an increase in flow rate through the system in order to mechanically remove foulants. In this case, it may be preferable to cease additions through injectors/controllers 130, 100 and 200 and to cease temperature control. In some systems, a bypass line, together with appropriate valves (note shown in system lOh), may be provided in order to bypass injectors/controllers 130, 100 and 200 and temperature controller 160. This may reduce the danger of damage to these components of the system due to high flow rates, and may also allow for higher flow rate by providing a larger diameter bypass. In order to flush the system, valve 230 may be opened (either manually or automatically due to a signal from controller 310 through a control line, not shown) and the pump of source 40 23 may be signalled via control line 330 to increase flow rate. Additionally or alternatively, to the increase in flow rate, cleaning solution may be added to the water in order to chemically remove foulants and/or to loosen their attachment to tube 20. Suitable cleaning solutions include chlorine solution (sodium hypochlorite solution) and acid (e.g. sulfuric acid or nitric acid). If cleaning solution is added, it may be preferable not to recycle the flush water to source 40, or else to treat it to neutralise it and remove harmful chemicals from it before returning it to source 40. In any event, flush water should be filtered using filter 380 before returning to source 40 in order to remove solids. Filter 380 may conveniently be a sand filter, a media filter, a microfilter, a settler, or a combination of these. Following cleaning with the flush water, the system may additionally be flushed with clean water (which, following filtration, may be returned to source 40) in order to remove residual cleaning chemicals. In order to resume normal irrigation, source 40 should be signalled to resume normal pump operation to restore normal irrigation pressures, and check valve 230 should be closed.

It will be understood that different configurations to those illustrated by systems 10a to lOh may be suitable. For example in system lOe, gas injectors 100 may all be fed from a single gas source rather than from separate gas sources, and other options have been mentioned in the above discussion. Additionally it will be understood from the earlier discussion that gas injectors 100 in the options of Fig. 1 may be replaced by a dosing device, for example comprising a pump and a tank, for adding a liquid to the water, whereby the liquid is, or comprises, a substance that can decompose to one or more gases. For example the liquid may be ammonium carbonate solution, which can decompose to generate carbon dioxide and ammonia.

In the description of the invention provided herewith, where mention is made of "a tube" of an irrigation system according to the invention, this may refer to multiple tubes of an irrigation system if these are present, as described in systems 10c to lOg of Fig. 1.

Various options are available for use with the present invention, as described below. Mulch. The tube may be at least partly surrounded by, or embedded in, a mulch. It may be surrounded around its entire circumference by the mulch over at least a portion, optionally the majority, of its length, or of the length that is to be buried in the soil. Mulches are well known in the horticulture and farming industries. Mulches commonly contain organic matter such as leaves, straw, or peat or other vegetable derived matter, optionally partially rotted. Mulch may serve to reduce evaporation of water and the freezing of roots. It may also serve to provide nutrients, which may be leached from the 24 mulch by the water leaving the tube of the irrigation system into the soil, so that those nutrients are made available to the crops irrigated by the irrigation system. The mulch may comprise or contain or be mixed with carbon and/or ash. This may be derived from burning waste plant materials. In certain farming practices it is common to burn off old crops. In other cases waste plant material may be obtained from land clearing, removal of weeds and/or other sources. The ash from this burning may be used in the mulch of the present invention. Additionally, if the burning is done in the appropriate equipment, in which the carbon dioxide can be collected and optionally stored, the carbon dioxide generated may be used in the gas injection step of the invention. The carbon and/or ash commonly comprise micronutrients and/or trace elements derived from the plants which were burned. This enables these materials to be recycled to promote healthy crop growth.

The mulch may be at least partially surrounded by a lining. The lining may serve to contain the mulch. Thus prior to being buried in the soil, the tube may be provided surrounded by mulch contained in the lining, so that when the tube is buried in the soil, the mulch is also present. The lining should be such that the water can pass through the mulch and into the soil once the tube and surrounding mulch are buried in the soil. The lining may be either porous, so that the water can pass out of holes in the lining, or it may be degradable in the soil, so that the lining degrades so as to allow the water to pass into the soil. The lining may be made of any suitable material. It may be for example be made of a polymeric film, a paper sheet or some other material. It may be made of a soluble sheet of material, so that in use, when exposed to water from the tube, the lining dissolves in order to allow the water to penetrate into the surrounding soil. The lining may be for example made from polyethylene, polyamide, polylactate, cellulose or an ester or ether thereof (e.g. methyl cellulose) or some other material. It may comprise a pressed fibre. It may be a fabric, for example a woven fabric. It may for example comprise cotton fabric. In some embodiments of the invention, the lining is non-porous, prior to the tube being buried in soil, and, while laying the tube (surrounded by mulch and lining) in the soil, or thereafter, holes or perforations may be formed in the lining. Thus for example, the tube, with mulch and lining, may be laid in a trench or ditch, and the lining may then be perforated with a knife or other suitable implement prior to the trench being filled with soil. In this manner, the perforations would be primarily in the uppermost portion of the lining. This favours direction of water from the irrigation system upwards towards the roots of a crop, and discourages direction of the water downwards to where it can be lost for example by diffusion to the water table.

Alternatively there may be no lining. In this case, the tube of the irrigation system may be embedded in the mulch when embedding the tube in the soil. Thus, for example, a suitable process may be to dig a trench to hold the tube, fill mulch into the bottom of the trench, lay the tube over the mulch, fill further mulch into the trench so as to cover and surround the tube, and then fill the remainder of the trench with soil.

Gases. The one or more gases may comprise carbon dioxide, nitrogen, ammonia or a mixture of any two or more thereof. Carbon dioxide is known to be essential for plant growth. Providing an increased concentration of carbon dioxide in the atmosphere surrounding the leaves of a plant can improve plant growth. It may provide more rapid growth. It may provide healthier growth. It may provide growth to a larger plant. It may improve crop yields. The present system provides the possibility of providing such an increased concentration directly to the plant by providing carbon dioxide in the irrigation water. From there it can pass up through the soil to the leaves which can absorb it. Nitrogen gas can be absorbed by legumes. In this case, nitrogen can be provided by the water exiting the irrigation system of the present invention directly to the roots of the legumes in order to provide improved delivery of the nitrogen. In the absence of such a system, plants would rely on diffusion from the atmosphere to the soil. This may be slow, particularly in the case where soils are relatively impermeable (e.g. clayey soils). For plants that are incapable of utilising nitrogen gas directly (such as non-leguminous plants), it may be advantageous to use a gas containing nitrogen, for example ammonia or an amine (e.g. methylamine).

The gases may be injected into the water by means of an injector. This may comprise a sparge, a frit, a porous injector or some other suitable injector. The injector may be located upstream of the tube, so that the gases are injected into the water before they enter the tube. Alternatively the injector may be located in the tube. For example the injector may take the form of a porous injection tube within (e.g. concentric with) the tube of the irrigation system. There may be more than one injector along the length of the tube. Thus, for example, there may be a gas tube running parallel to the tube, with injectors for passing gas from the gas tube to the water in the tube at intervals along the length. The injectors may be spaced at distances of about 5 to about 50m, or about 5 to 25, 5 to 10, 10 to 50, 25 to 50 or 10 to 30m, e.g. every 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50m along the length. They may be evenly spaced along the tube or may be unevenly spaced therealong.

The gas(es) may be in solution in the water when it exits the tube into the soil (or into the mulch) or it may be in the form of bubbles, optionally microbubbles, or it may be 26 partially in solution and partially present as bubbles. As noted elsewhere, the irrigation system may have a temperature controller for controlling the temperature of the water. In cases where the water needs to be cooled prior to use, it may be advantageous to perform the cooling prior to injecting the gases. It is known that gases are more soluble in cold liquids than in hot liquids. Thus cooling the water prior to injection of gas may improve the absorption of gas by the water. pH Control: The irrigation system may additionally comprise a pH controller for controlling the pH of the water to a suitable pH for growing a crop, e.g. between about 6 and about 8. The pH may be controlled to between about 6 and about 8, or about 6 to 7, 7 to 8, 6.5 to 7.5, 6.8 to 7.2, 6 to 6.5, 6.5 to 7, 7 to 7.5 or 7.5 to 8, e.g. about 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9 or 8. The optimum pH will depend on the nature of the plant to be irrigated by the irrigation system. The pH controller may dose a pH controlling liquid into the water. The pH controlling liquid may be stored in a reservoir. The pH controlling liquid may be an acid, an alkali or a buffer. There may be more than one pH controlling liquids, each stored in a separate reservoir, and the pH controller may control the different feed rates of these liquids to achieve the desired pH. The pH controlling liquid may comprise a buffer in order to achieve the desired pH. It may for example comprise a phosphate based buffer or some other type of buffer. The pH controller may comprise a pH sensor (e.g. a pH electrode) for detecting the pH of the unadjusted and/or adjusted water. In particular, there may be a feedback system so that the pH controller can provide the appropriate pH control depending on the pH of the adjusted water. It may be desirable to adjust the pH before addition of carbon dioxide to the water. It will be understood that dissolving carbon dioxide in water can lower the pH of the water. If the pH of the water is adjusted after addition of carbon dioxide, then, when carbon dioxide leaves the water and is passed into the atmosphere surrounding the leaves, the pH of the water may rise to a level that is not conducive to growth of the crop. If it added after adjustment, the water in the tubes may be at a lower than optimum pH for crop growth, but may return to a desirable pH once the carbon dioxide comes out of solution. In this case, since the pH of the water will be relatively low, the carbon dioxide is likely to readily come out of solution as desired.

Temperature Control: The temperature controller may be capable of controlling the temperature of water to a temperature suitable for growing a crop. The suitable temperature may be between about 10 and about 40°C, depending on the nature of the crop, or may be outside this range. The temperature may be about 10 to 30, 10 to 20, 20 to 27 40, 30 to 40, 20 to 30, 15 to 30 or 15 to 20°C, e.g. about 10, 15, 20, 25, 30, 35 or 40°C. The desired temperature may be adjusted depending on the preferred temperature (e.g. the temperature for optimum growth or optimum yield) of the crop to be irrigated, and also depending on the solubility of the gases added to the water. Thus for example, if a summer crop is to be grown in winter, the water may be heated to a temperature suitable for the summer crop. Alfalfa has a preferred germination temperature of about 25°C. If alfalfa is to be sown in winter, it is preferable that the water be heated sufficiently to bring the soil temperature to about that temperature. Similarly, eggplant have a minimum germination temperature of about 16°C, so to germinate these in a cold winter climate, the water should be heated sufficiently to bring the soil temperature to at least this temperature, and preferably to about 24-32°C (the preferred germination temperature for eggplant). In some cases, if a cool climate crop is to be grown in a hot summer climate, it may be preferable to cool the water so as to cool the soil surrounding the crop. Rapeseed has a preferred germination temperature of about 15 to 20°C. Thus in hot summer temperatures it may be preferred to cool the water for this crop so as to achieve this soil temperature range. A heater for use in a temperature controller/adjuster may be powered by geothermal and/or solar energy, e.g. by conversion of the geothermal energy and/or solar energy into electricity and use of that electricity to power the heater, or else by direct use of the solar and/or geothermal energy for heating. A cooler for use in a temperature controller/adjuster may also be powered by geothermal and/or solar energy, e.g. by conversion of the geothermal energy and/or solar energy into electricity and use of that electricity to power the cooler. As noted earlier, the method of the invention may comprise adding a substance that can decompose to produce one or more desired gases. In this case, the decomposition rate may depend on the temperature of the water, and thus the temperature may be adjusted to achieve a desired decomposition rate, i.e. a desired rate of evolution of the gas(es). The temperature control may use a natural source of energy. It may be a solar powered temperature controller or temperature adjuster. It may be a geothermal powered temperature controller or temperature adjuster. The temperature controller or temperature adjustor may comprise a solar collector or a geothermal collector. Thus solar power and/or geothermal power may be used in order to power the controller or adjustor (optionally to provide heat therefore). The temperature controller or adjuster may be capable of raising the temperature of the water in the tube by sufficient to achieve the desired temperature. It may be capable of raising the water temperature by between about 5 and about 40 Celsius degrees, or about 5 to 30, 5 to 20, 5 to 10, 10 to 40, 28 to 40 or 10 to 20 Celsius degrees, e.g. about 5, 10, 15, 20, 25, 30, 35 or 40 Celsius degrees. The temperature controller or adjuster may comprise a temperature measurer, e.g. a thermocouple, a thermometer etc. for measuring the temperature of the water. It may comprise a thermostat for ensuring that the desired temperature, or a temperature within a desired temperature range, is achieved. Since the water may lose heat as it passes along the tube, there may be more than one temperature controller or adjuster along the length of the tube. These may for example be spaced at distances of about 5 to about 50m, or about 5 to 25, 5 to 10, 10 to 50, 25 to 50 or 10 to 30m. They may be spaced so as to maintain the temperature of water in the tube (or exiting the tube) within a desired range (e.g. within about 5°C, or within about 4, 3, 2 or 1°C) along the length of the tube. They may be evenly spaced along the tube or may be unevenly spaced therealong. The tube may be constructed from a thermally insulating material. This may reduce thermal losses from the water through the wall of the tube. It may reduce the number (and/or increase the spacing) of temperature controllers along the length of the tube. The thermally insulating material may for example comprise a polymeric material, e.g. a polyolefin or polyurethane.

Location in Soil: The tube, optionally surrounded by mulch may be adapted to be buried in soil. This may involve providing a tube of appropriate flexibility, strength, resilience, degradation resistance (especially biodegradation resistance) etc. to resist the process of burying it in the soil and to resist degradation and/or damage whilst in the soil. It may be designed to resist that degradation and/or damage for at least 1 year, or at least 2, 5, 10, 20, 50 or 100 years, or for up to at least 1, 2, 5, 10, 20, 50 or 100 years, or about 1 to about 100 years, or about 2 to 100, 5 to 100, 10 to 100, 20 to 100, 50 to 100, 1 to 50, 1 to 20, 1 to 10, 1 to 5, 5 to 50, 10 to 50 or 20 to 50 years, e.g. for about 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100 years. It may be made of a suitable material, and have suitable wall thickness, to avoid mechanical damage.

In order to facilitate burying the tube in the soil, it may be advantageous for the tube to be at least partially flexible. It may be advantageous to have rigid portions of the tube connected by flexible portions. In some embodiments the flexible portions are concertinaed so as to facilitate flexing thereof. In some embodiments it may be advantageous to have porous rigid portions of the tube connected by non-porous flexible portions thereof. For example in system 10a of Fig. 1, the rigid portions may be adapted to pass under the crop plants 30, whereas the flexible portions may be suitable for forming the bends at the ends of rows. In other embodiments it may be advantageous to 29 have porous rigid portions of the tube connected by flexible porous portions thereof. This may be advantageous in cases where the rows of crops to be irrigated are very long. An at least partially flexible tube may facilitate transportation. In other embodiments the tube may be supplied in portions adapted to be connected together, for example by screw threading at the ends of the portions, gluing, matching flanges at the ends of the portions (which may be clampable or joinable in some other fashion, e.g. by bolts). In this case the portions of the tube may be laid in place in the soil prior to being joined together to form the tube.

The specification also describes a method for irrigating soil. The method comprises providing an irrigation system as described herein wherein the tube is at least partially buried in the soil. One or more gases may be injected into the water, which is then passed to the tube interior at a constant pressure, such that the water passes out of the tube through the tube wall via the pores and passes into the soil.

The soil may have a crop therein, so that the irrigation of the soil facilitates or improves, growing the crop. In the context of the present specification, a "crop" may be any intentionally grown plant or group of plants. It may be grown for sale of the entire plant, or for the purposes of harvesting fruit or leaves for sale or consumption by humans or animals or for the purpose of extracting a medicinal substance or for some other purpose. The crop may be any crop that requires irrigation. It may be a fruit, a vegetable, a grain, a stock feed, medicinal crop or some other type of crop. It may be for example a legume. It may be a tree, a bush, a shrub, a grass or some other type of crop. The tube may be located in the soil beneath the crop. It may be located beneath the roots of the crop, or it may be located amongst or beside the roots of the crop. In many cases, the crop may initially be planted above the tube, and the roots of the crop may grow down and around and/or past the tube as the crop grows and matures. The tube may be made of a material that is resistant to rupture by the growing roots of the crop.

Thus the invention also provides a method of growing a crop. In this method the tube of an irrigation system according to the invention is buried in soil. The crop is then planted in the soil above the tube. Water is passed from a water source to the tube interior under a constant pressure. The water then passes out of the tube through the tube wall and passes into the soil, thereby irrigating the crop. One or more gases may be injected into water using a gas injector prior to the water passing out of the tube.

The water may pass out of the tube, via the pores of the tube wall, into the soil at a rate suitable for growing the crop. This will depend on the nature of the crop, and may also depend on such factors as the rainfall, other sources of moisture in soil, ambient temperatures etc. The water flow rate may be between about 0.01 and about 10 litres per hour per metre of tube length, or about 0.01 to 5, 0.01 to 1, 0.01 to 0.5, 0.01 to 0.1, 0.01 to 0.05, 0.01 to 0.02, 0.05 to 10, 0.1 to 10, 0.5 to 10, 1 to 10, 5 to 10, 0.05 to 5, 0.05 to 1, 0.05 to 0.5, 0.05 to 1, 0.1 to 1, 0.1 to 0.5 or 5 to 1 litres per hour per metre of tube length, for example about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 litres per hour per metre of tube length, or may be some other rate, depending on the factors outlined above.

As noted earlier, the tube of the irrigation system may be provided with surrounding mulch, optionally encased in a lining. The mulch surrounding the tube may between about 0.1 and about 10 times the thickness of the tube, or about 0.1 to 5, 0.1 to 2, 0.1 to 1, 0.1 to 0.5, 0.5 to 10, 1 to 10, 2 to 10, 5 to 10, 0.5 to 5, 0.5 to 2, 0.5 to 1 or 1 to 2 times the thickness of the tube, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 times the thickness of the tube. The thickness may be between about 1 and about 50cm, or between about 1 and 40, 1 and 30, 1 and 20, 1 and 10,1 and 5, 2 and 50, 5 and 50, 10 and 50, 20 and 50, 5 and 2, 5 and 10 or 2 and 5cm, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45 or 50cm.

The step of burying the tube in the soil may comprise the steps of: a) forming (e.g. digging) a trench or ditch in the location where the tube will be buried; b) optionally locating mulch and/or other required material (e.g. fertiliser, for example slow release fertiliser, moisture release pellets, trace minerals, pesticide etc.) in the tube; c) locating the tube, optionally surrounded by mulch, in the trench; d) optionally locating further mulch and/or other required material in the trench; and e) filling the remaining trench with soil.

Step a) may be conducted manually, or using machinery, e.g. a tractor. The decision as to whether to form the trench manually may depend on the length and required depth of the trench. The trench should be sufficiently wide to accommodate the tube as well as any mulch and other required materials that are used. It should be sufficiently deep to accommodate the tube as well as any mulch and other required materials that are used. In addition, sufficient depth should be allowed for additional soil to be added above the tube and/or mulch. The depth of additional soil may be sufficient to allow for the root system 31 of the plant, or may be greater than that (to allow for a distance between the root system and the tube) or less than that (so as to allow the root system to at least partially surround the tube. The trench should be approximately the same length as the desired length of a row of the crop. Thus the trench may, depending on the size of tube, presence or absence and (if present) thickness of mulch, and nature of the crop, be between about 10cm and about lm deep or more. If may for example be about 10 to 50, 10 to 20, 20 to 100, 50 to 100, 20 to 50 or 30 to 70cm deep, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100cm deep, or may in some circumstances be deeper, e.g. 1.1, 1.2, 1.3, 1.4, 1.5,1.6, 1.7, 1.8, 1.9 or 2m deep. It may be between about 5cm and about lm wide, or about 5 to 50, 5 to 20, 5 to 10, 10 to 100, 20 to 100, 50 to 100, 20 to 50 or 30 to 60cm wide, e.g. about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100cm wide.

If the region in which the tube is located is sloped, it is preferable that the tube runs down the hill (i.e. the water enters the tube at the higher end) if the slope of the region is less than about 2°. This helps to reduce pressure drops along the tube and reduces energy consumption. If the slope is greater than about 2°, it may be preferable to run the tube across the contour of the region in order to obtain a more even pressure distribution along the tube. If long and/or steep downhill portions of tube are necessary, it may be advantageous to install pressure reducers at one or more locations along the tube inside the tube in order to reduce the pressure drop and thereby provide a more even water flow rate along the tube.

In step b), the mulch and/or other required material is preferably located along the length, or the majority of the length, of the trench. In step c) the tube may be at least partially embedded in the mulch and/or other required material. In the event that the tube is provided in portions, step c) may comprise locating the portions in the trench and coupling them together to form the tube, or it may comprise coupling the portions together to form the tube and then locating the tube in the trench, or it may comprise coupling some portions together to form larger portions, locating the larger portions in the trench and then coupling the larger portions together to form the tube. The tube (i.e. the centre of the tube) may be buried in the soil to a depth of between about 10 and about 100cm, or about 10 to 50, 10 to 20, 20 to 100, 50 to 100, 20 to 50, 30 to 45 or 30 to 70cm, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100cm. Step d) may comprise at least partially burying the tube in the mulch. It may comprise surrounding the tube with the mulch. It should be noted that even in the event that the tube is provided surrounded by 32 mulch (encased in a lining) further mulch or other required materials may be used in steps b) and d).

Once the tube is buried in the soil, the crop may be planted, preferably above the tube. Alternatively seeds of the crop may be included in the soil used to bury the tube in the soil, or in the mulch used to cover the tube in the soil. In some cases the tube may be provided with surrounding mulch (as previously described) wherein seeds of the crop are located in the mulch, so that, once provided with water from the tube in use, the seeds can grow. This step may use any of the well known processes for planting crops. It may comprise hand planting or machine planting. It may use a tractor. In some instances it may comprise scattering or sowing seed over an area having one or more tubes buried therein and connected to a water source according to the present invention. The planting may comprise planting seeds or it may comprise planting plants. The irrigation of the crop according to the present method may be continuous or it may be discontinuous. Thus a continuous pressure of water may be applied to the tube interior, leading to a roughly constant flow of water out of the tube through the pores of the tube wall. Alternatively the flow may be controlled (optionally by a controller, for example a computer) so that a cycle of alternating flow periods and no-flow, or low flow, periods is implemented. For example flow periods may be for between about 1 hour and about 24 hours (or about 1 to 18, 1 to 12, 1 to 6, 1 to 3, 3 to 24, 6 to 24, 12 to 24, 3 to 12, 3 to 6 or 6 to 12 hours, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 hours) and no-flow, or low flow periods may be between about 1 hour and 24 hours (or about 1 to 18, 1 to 12, 1 to 6, 1 to 3, 3 to 24, 6 to 24, 12 to 24, 3 to 12, 3 to 6 or 6 to 12 hours, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 hours). In this context, "low flow" should be taken to refer to a flow rate lower than that during the flow periods. It may be for example about 10 to 90% of the flow during the flow periods, or about 10 to 50, 10 to 20, 20 to 90, 50 to 90 or 20 to 50% thereof, e.g. about 10, 20, 30, 40, 50, 60, 70, 80 or 90% thereof. In some cases the low flow may be even lower, e.g. about 5, 2 or 1% of the flow during the flow periods. This may be sufficient to retain some residual moisture in the soil, particularly in desiccating environments such as desert summer climates. In some embodiments continuously varying flow may be implemented, for example a sinusoidal variation of flow with time. Other varying flow regimes may be implemented depending on the requirements of the crop and the prevailing conditions. The flow may be controlled by means of the water source (by varying the applied water pressure) or by means of valves or flow controllers 33 in the tubes or, in the case of a manifolded system, in the manifold. It has previously been discussed that different flow rates, temperatures etc. may be applied to different tubes in a manifolded irrigation system. In the same way, different flow cycles may also be applied to different tubes, for example to optimise irrigation for different crops using a single manifolded irrigation system.

The irrigation system of the present invention may comprise a controller, e.g. a computer based controller, for controlling the different components of the system, such as the gas injector and/or dosing device, the temperature controller, the pH controller and the flow controllers. The controller may also receive input from sensors (e.g. temperature sensors, flow sensors, pH sensors and gas concentration sensors) in order to provide feedback for the control of those components.

The invention also provides a crop when grown by the method described above. The crop may be grown more rapidly and/or with greater yield and/or with improved quality relative to the same crop grown in the absence of irrigation according to the present invention.

Features which may be present in the irrigation system described herein include the following: 1. Mulch: The mulch may serve one or more of the following functions: minimising water losses, providing slow release of trace elements and/or other nutrients into the soil, and provide structure for the soaker hose (tube). The nature of the mulch may be adapted to the specific requirements of the crop which is grown using irrigation from the irrigation system. For example, a particular crop may require a high level of potassium, and consequently a mulch containing high potassium levels may be used. By ensuring that the tube of the irrigation system is surrounded by the mulch (optionally that the tube is located in the middle of the mulch), the amount of water lost into ground water is reduced, and therefore more water is accessible by the roots of the plants of the crop. As the mulch slowly decomposes, it improves the structure of the soil as trace elements leach from the mulch into the soil. 2. Mulch lining: Commonly a mulch will provide much of its own structure. A biodegradable lining may be used in order to facilitate the process of laying the tube surrounded by the mulch into the soil. Alternatively a lining having holes therein may be used to facilitate the tube laying process. In this event, water, nutrients, trace elements etc. may pass from the mulch to the soil surrounding it through the holes. The holes may be of 34 a size, number and spatial distribution to permit sufficient passage of water, nutrients and trace elements to pass substantially unimpeded into the soil from the mulch. 3. Water purity/quality: The purity and quality of the water used in the present irrigation system is important in the use of the system. The quality and purity of the water may be adapted to the specific crop to be irrigated by the irrigation system. Many crops require a neutral or close to neutral pH (i.e. pH about 7) for optimum growth. When the pH is outside the optimum range for the particular crop, growth may be stunted or prevented. The provision of water of an appropriate quality and purity may aid in maintaining soil structure, soil quality and available micro and macro nutrients for the crop. As noted, the irrigation system may comprise a pH controller for controlling the pH of the water to an appropriate pH for the crop. The appropriate pH may depend on the nature of the crop, and may be between about 6 and about 8. In some embodiments of the invention the system may additionally comprise one or more injectors for injecting nutrients and/or other substances (trace elements etc.) into the water. This may be particularly useful in cases where no mulch is used in the system, or where the mulch that is used does not contain sufficient of the nutrients and/or other substances required by the specific crop for optimum growth. The injector(s) may also be used for injecting one or more herbicides into the water in order to prevent or inhibit growth of unwanted plants such as weeds. These herbicides should not prevent growth of the plants of the crop to be irrigated by the system. 4. Reduced soil soakage and water loss: A problem with previous irrigation systems is that much of the water is lost through evaporation and leaching. Most of the losses through evaporation occur on the surface of the soil whilst much water is lost into the water table by leaching (especially in sandy soils). Soil leakage and water losses are reduced in the present irrigation system by the following: • by pumping water into the soil beneath the surface, evaporation is minimised. With low water loss through evaporation, more water is available to the roots of the crop, thus promoting growth. Less water is required in order to grow a crop using the present irrigation system than with conventional irrigation systems. This is important under conditions of limited water availability. • the presence of mulch may serve to reduce water losses through leaching of subsurface water. Leaching through the soil into the water table is a major problem with traditional irrigation methods. As the water leaches to the water table, nutrients may also be leached to the water table. The presence of mulch therefore may improve availability of water and of nutrients to the roots of the crop. Additionally, mulches commonly contain trace elements and other nutrients, and can act as slow release fertilisers.

. Carbon: In some embodiments the mulch, if present, contains a form of carbon. This may for example be ash from burnt trees, shrubs and bushes. This ash commonly contains micronutrients, trace elements etc. enabling the ash to act as a fertiliser. In this way it may act as a natural equivalent of conventional fertilisers such as pot ash super which is commonly used in farming systems. Commonly the ash acts as a fast acting fertiliser and the remainder of the mulch acts as a slow release fertiliser. In broad acre cropping much of the stubble from previous crops is burned and then ploughed into the soil. This provides the soil with trace elements, however much of these are lost through the ash not being available directly at root level for the subsequent crop. In use, the present irrigation system provides such trace elements etc. at the root level of the crop, thereby reducing the loss of carbon and micronutrients, trace elements etc. 6. Soil type correction: Many soils in Australian have been depleted through over cropping and loss of nutrients to the water table, thereby making the soils acid or alkaline. Soils may be corrected through use of appropriate fertilisers or crops may be grown which have a resistance to a particular soil problem. For example lucerne, which is a drought tolerant crop, will grow in slightly acid soils. Both of these corrections are unsustainable due to cost and the need for crop rotation. Using the irrigation system of the present invention, correction of soil types may be conducted below the soil surface. The mulch and carbon may ensure that the soil contains nutrients, trace elements etc. required by the crop, and the gas(es) introduced into the water ensure that the crop has an adequate supply of these. This ensures that the crop does not deplete the soil of the nutrients etc. to the extent that the soil contains insufficient of them to sustain healthy crop growth. The mulch and/or ash may be selected for the particular deficiencies of the soil in which the irrigation system is used. For example, when used in an acidic soil (pH 4.5 to 6) a desirable mulch may contain organic alkaline components. This would allow the alkaline components to be slowly released into the soil in order to raise the pH to a more suitable level, for example between about 6 and about 8. The mulch may be combined with suitable additives in order to provide appropriate materials to the soil. For example gypsum may be used to increase the pH of the soil, fertilisers may be used to increase the nutrient level of the soil etc. It will be understood that the nature and quantity of such additives will depend on the nature of the soil, the requirements of the crop to be irrigated 36 etc. Additionally or alternatively, additives may be added to the water to promote healthy growth of the crop. For example soluble nutrients, pesticides etc. may be dosed into the water prior to its exiting the tube so as to promote crop growth. 7. Gas injection: For healthy growth, plants require carbon dioxide (CO2) and nitrogen. Carbon dioxide is absorbed from the atmosphere through the leaves. Nitrogen is absorbed from the soil through the roots. Many plants absorb nitrogen in the form of nitrates and/or organic nitrogen compounds. Certain plants, legumes, are capable of directly fixing nitrogen through specialised root nodules. Plant metabolism provides growth and generates oxygen (O2) which is given off into the atmosphere. Other plants require supply of nitrates or other nitrogen compounds. Nitrates may be generated by the action of lightning atmospheric nitrogen and may be subsequently brought into the soil by rainwater. Other nitrogen compounds may be provided by fertilisers.

In the present irrigation system carbon dioxide and/or nitrogen and/or ammonia may be injected into the water as gases in order to provide these to the roots of the crop if required. This enables direct utilisation of these gases by the crop. Carbon dioxide injected into the water can diffuse up through the soil to be absorbed by the leaves. Nitrogen will be concentrated around the roots, and, for plants that are capable of fixing the nitrogen, will be taken up by the roots as required. Ammonia may be utilised by the roots of plants that can not fix nitrogen. Carbon dioxide may be obtained by burning of coal or other carbonaceous materials. 8. Water temperature: A problem with growing crops in Australia is that of extreme temperatures. The problem of extreme heat in summer and/or frost in winter often dictate which crops can be grown in which locations and when. By adjusting the temperature of the water which enters the tube of the irrigation system, the soil temperature may be maintained at a suitable temperature for growth of a particular crop. This provides farmers with the advantage of being able to grow a particular crop year round. Adjusting the water temperature also ensures that the nutrients which reach the plants are accessible to those plants. 9. Heat transfer: Heat energy for heating the water in the present irrigation system (if required) may be obtained from any suitable source. It may be electrical heating, or it may be solar heating or it may be geothermal heating or it may be heating from combustion of a suitable fuel. The fuel may be gas (e.g. natural gas). It may be plant material, whereby the heat energy may be used for heating as described, and the residual ash may be used in the mulch (if present) surrounding the tube of the irrigation system. It may be coal, in 37 particular it may be clean coal, so as to produce relatively minor quantities of pollutants. The heat energy may be obtained by eddy current heating, as described in W01995/025416, the contents of which are incorporated herein by cross reference. The heat energy may be stored prior to its use for heating the water. It may be for example stored in a solid graphite heating block.

Figure 2 illustrates an irrigation system according to the present invention. Fig. 2 shows a cross-section of the tube of the irrigation system in operation. Irrigation system 200 comprises hollow tube 210 comprising tube wall 220 having pores (not shown in Fig. 2) extending therethrough. Tube wall 220 defines tube interior 230, whereby water can pass from tube interior 230 through tube wall 220 via the pores. Tube 220 is conveniently made of PVC, and has pores, or holes, of about 1mm diameter regularly along its length, to allow water to pass through wall 220. Tube 220 has an outside diameter of about 20 to about 40mm, and an inside diameter of about 15 to 35mm, and a wall thickness of about 2 to 5mm. Tube 210 is surrounded by mulch 240, which contains particles of ash 250. These may be obtained from burning of timber cleared from the land in order to plant crops. The thickness of mulch 240 is about 5cm. When laying tube 210, it is convenient to enclose mulch 240 in a lining to facilitate burying tube 210 and mulch 240 in the soil. However in use, the lining may biodegrade, and after a period of use, no lining may remain.

Interior 230 is coupled to a source of water (not shown in Fig. 2), said source being capable of maintaining a constant water pressure in interior 230. Tube 210 is coupled to a gas injector for injecting a mixture of carbon dioxide and nitrogen into the water prior and also to a pH controller for controlling the pH of the water to between about 6 and about 8. Neither the injector nor the pH controller is shown in Fig. 2. Tube 210 is buried in soil to a depth of about 30-45 cm. Crop 260 is growing above tube 210, with root system 265 extending below the soil surface towards tube 210. Growth of plant 260 is encouraged by sun and rain in the natural way. In operation of irrigation system 200, water having the appropriate concentration of nitrogen and carbon dioxide is fed to tube interior 230 and passes through holes in wall 220 into mulch 250. In passing through mulch 250 the water can extract nutrients, trace minerals etc. to make them available to plant 260. Some of the water exiting tube 210 may diffuse in the direction of arrows 280 towards the water table and be lost. This may in some cases be discouraged by having more holes in the upper side of tube 210 than in the lower side. In any event, much of the water passing out of tube 210 will pass upwards in the direction of arrows 290, and be available to roots 270. 38 This provides both water and nutrients to these roots. Additionally, water passing out of tube 210 may release its dissolved gases. Nitrogen, if used, will be available for use directly by roots 270 (in the event that plant 260 is capable of fixing nitrogen). Carbon dioxide will pass upwards through the soil and enter the atmosphere in the direction of 5 arrows 290. This provides a high carbon dioxide atmosphere in the vicinity of plant 260, thereby encouraging growth.

Received 10 June 2009 I ' 39 ' .

Claims

Claims:

1. An irrigation system comprising: • a hollow tube, said tube comprising a tube wall having pores extending therethrough, said wall defining a tube interior, whereby water can pass from the tube interior through the tube wall via said pores; • a temperature controller to control the temperature of the water or a temperature adjustor to adjust the temperature of the water; • either a carbon dioxide injector for injecting a gas comprising carbon dioxide into the water prior to said water passing out of the tube, or a dosing device for adding into the water a substance capable of releasing carbon dioxide prior to said water passing out of the tube; • a control unit for adjusting one or more of temperature of the water, rate of injecting carbon dioxide into the water, rate of addition to the water of the substance capable of releasing carbon dioxide and pH of the water; and • one or more carbon dioxide sensors located downstream of the injector or dosing device, said one or more sensors being coupled to the control unit for sending a signal relating to carbon dioxide concentration in the water to the control unit.

2. The irrigation system of claim 1 wherein the temperature controller or temperature adjustor comprises a solar collector and/or a geothermal collector.

3. The irrigation tube of claim 1 or claim 2 wherein said hollow tube is adapted to be buried in soil.

4. The irrigation tube of any one of claim 1 to 3 wherein said tube is made of a material that is resistant to rupture by growing roots of a crop.

5. The irrigation system of any one of claims 1 to 4 additionally comprising a source of water coupled to the tube interior, said source being capable of passing water to said tube interior under pressure.

6. The irrigation system of claim 5 wherein the source is capable of passing water to said tube interior under constant pressure.

7. The irrigation system of any one of claims 1 to 6 comprising one or more moisture sensors for sensing the moisture content of soil surrounding the tube and a feedback system from said sensor(s) to a pressure regulator in the source so that, in use, the pressure regulator can adjust the pressure to ensure a desired moisture content of the soil. Amended Sheet IPEA/AU 40 PCT/ATO008/001153 Received 10 June 2009

8. The irrigation system of claim 1 comprising one or more carbon dioxide sensors locatable in soil surrounding the tube of said system, said sensor(s) being coupled to the control unit.

9. The" irrigation system of any one of claims 1 to 8 additionally comprising a pH controller for controlling the pH of the water to a desired pH or a pH.. adjustor for adjusting the pH' of the water to the desired pH.

10. The irrigation system of claim 9 wherein the desired pH is between about 6 and about 8.

11. The irrigation system of any one of claims 1 to 10 additionally comprising a chemical addition system for adding chemicals to the water.

12. The irrigation system of any one of claims 1 to 11 wherein the tube is at least partly surrounded by a mulch.

13. The irrigation system of claim 12 wherein the mulch is at least partially surrounded by a lining.

14. The irrigation system of claim 13 wherein the lining is either porous or is degradable in soil or is both porous and degradable in soil.

15. The irrigation system of claim 13 or claim 14 wherein the lining is biodegradable.

16. The irrigation system of any one of claims 13 to 15 wherein the mulch comprises an ash.

17. " The irrigation system of any one of claims 1 to 16 comprising a fine filter outside the tube capable of preventing particles from the soil or mulch from entering or clogging the pores of the tube.

18. The irrigation system of any one of claims 1 to 17 additionally comprising a flush system for cleaning the system once some degree of fouling of the pores has occurred.

19. The irrigation system of claim 18 wherein said flush system comprises a dosing pump for adding cleaning agents and/or defouling agents to flush water.

20. The irrigation system of any one of claims 1 to 19 comprising more than one hollow tube, said tubes being manifolded using one or more manifold and -each of said tubes comprising a tube wall having pores extending therethrough, said wall defining a tube interior, whereby water can pass from the tube interior through the tube wall via said pores.

21. A method for irrigating soil comprising:

Amended Sheet

IPEA/AU 41 *;PCT/AU2008/001153 Received 10 June 2009;• providing an irrigation system according to any one of claims 1 to 10, wherein the tube is at least partially buried in the soil,;• either injecting carbon dioxide into the water prior to said water passing out of the tube or adding to the water a substance capable of releasing carbon dioxide;;• detecting a concentration of carbon dioxide in the water;;• generating a signal relating to said concentration of carbon dioxide;;• controlling or adjusting one or more of the temperature of the water, a rate of injecting carbon dioxide into the water, a rate of addition to the water of the substance capable of releasing carbon dioxide and pH of the water in response to said signal; and;• passing the water to the tube interior under pressure,;such that the water passes out of the tube through the tube wall via the pores thereof and passes into the soil.;22. The method of claim 21 wherein the pressure is a constant pressure,;23. The method of claim 21 wherein the pressure is controlled so that a cycle of alternating flow periods and no-flow, or low flow, periods is implemented. .;

24. The method of any one of claims 21 to 24 wherein the pH is controlled at, or adjusted to, between about 6 and about 8.;

25. The method of any one of claims 21 to 24 additionally comprising adding one or more chemicals to the water.;

26. The method of claim 25 wherein the one or more chemicals are selected from the group consisting of a fertiliser, a nutrient, a trace mineral, a pesticide, a weedicide, and combinations of any. two or more of the above..;

27. The method of any one of claims 21 to 26 wherein the soil has a crop therein and the tube is located in the soil beneath the crop.;

28. A method of growing a crop comprising:;• providing an irrigation system according to any one of claims 1 to 20;;• burying the tube of the irrigation system in soil;;• planting the crop in the soil above the tube;;• passing water into the tube of the irrigation system;;• either injecting carbon dioxide into the water prior to said water passing out of the tube or adding to the water a substance capable of releasing carbon dioxide;;• detecting a concentration of carbon dioxide in the water;;Amended Sheet;IPEA/AU;PCT/AU2008/001153 4*2 Received 10 June 2009 • generating a signal relating to said concentration of carbon dioxide; • controlling or adjusting one or more of the temperature of the water, a rate of injecting carbon dioxide into the water, a rate of addition to the water of the substance capable of releasing carbon dioxide and pH of the water in response to said signal; and • passing the water to the tube interior under pressure, optionally under a constant pressure; such that the water passes out of the tube through the tube wall via the pores thereof and passes into the soil, thereby irrigating the crop.

29. The method of claim 28 wherein the pressure is constant pressure.

30. The method of claim 28 or claim 29 wherein the burying is such that the slope of the tube is less than or equal to 2°.

31. The method of any one of claims 28 to 30 additionally comprising the step of adjusting the temperature of the water, or of controlling the temperature of the water to a temperature suitable for growing the crop..

32. A crop grown by the method of any one of claims 28 to 31. Amended Sheet IPEA/AU