AU633679B2 - Soil sterilizer - Google Patents

Description

38360 PJW:LL COMMONWEALTH OF AUSTRALIA Patents Act 1952 Form COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: 61 3 67 Class Int. Class Application No Lodged Complete Application No Specification Lodged Published Priority: Related art: TO BE COMPLETED BY APPLICANT Name of Applicants: Address of Applicants: Actual Inventors: Address for Service: BRYAN ROBINSON, FRANK PERRE AND PAT PERRE respectively of Virginia and Loxton, all State of South Australia, Commonwealth of Australia BRYAN ROBINSON, FRANK PERRE AND PAT PERRE Care of COLLISON CO., 117 King William Street, Adelaide, South Australia, 5000 PATENT, TRADE MARKS DESIGNS

SUB-OFFICE

invention entitled: 2 4 JAN 991 SOUTH AUSTRALIA Complete Specification for the SOIL STERILIZER The following statement is a full description of this invention, including the best method of performing it known to us: -i This invention relates to sterilization of the upper layers of topsoil by microwave energy.

Sterilization of the upper surface of top-soil is an important part of modern intensive agricultural methods. Soil sterilization increases production yields by decreasing plant disease and therefore crop loss.

The term sterilization in this specification is not used in its strictest sense but rather in the sense of meaning killing of plant pathogenic microorganisms in the 1 0 upper layer of top soil so as to substantially reduce the likelihood of infection of plants subsequently cultivated therein. In one form this could be considered to be achieved by heating the upper layers of the top soil to 600C or greater, however in certain circumstances this may not be sufficient, with greater temperatures being required.

The most effective current method of sterilization is the application of chemical sterilants to the upper layers of topsoil. However increasing awareness of the undesirable side-effects of such chemical sterilants such as the accumulation of toxic residuals has led to the banning of most effective broad spectrum sterilants, and the realisation that the side-effects of their use is highly undesirable. Some specific chemical sterilants, including many that are active against a narrow spectrum of organisms, are still available and are not as yet known to have serious side effects, however, application of more than one sterilant is necessary if a broad range of organisms are to be inactivated, and it seems likely that progressively more sterilants will be found to have undesirable side effects.

Sterilization by the use of heat is a method in use not known to have long term side effects however its application is somewhat awkward. One form of heat sterilization is by the injection of steam into the upper layer of the topsoil. This method has the disadvantage that large amounts of water have to be supplied to the site of sterilization, and a large amount of energy is needed to heat the water to produce steam.

Another method using heat for sterilization is "solarisation". Solarisation involves 3 5 covering the surface of soil to be sterilized with a sheet of material such as black heavy duty plastics. Irradiation of the sheet by the sun leads to an increase in the temperature of the upper layers of the top soil beneath the sheet. High air temperatures are required for this application to be effective and Solarisation does not become effective until the air temperature approaches 400C.

Solarisation thus is not a reliable method and is thus subject to the variation of weather patterns and is not suitable for colder climates.

This invention addresses problems associated with the above methods and results from the discovery of a means by which microwave irradiation can be applied to the upper surface of topsoil so as to have a sterilizing effect.

Thus the invention could be said to reside in an apparatus for sterilizing a layer of soil immediately beneath a soil surface, said apparatus adapted to be moved over a ground surface, and including a microwave generator said apparatus including a microwave cavity providing a microwave-impermeable passage way 1 5 for microwave radiation to said soil surface, and including sealing means for inhibiting leakage of microwaves from between peripheral edges of a lowermost portion of said cavity and the soil surface and said microwave generator being adapted to radiate microwaves into the layer of soil through the microwave cavity, so as to have a sterilizing effect on the layer of soil.

In preference the apparatus includes an electricity generator and voltage regulator for providing electrical power of a sufficiently uniform voltage for said microwave generator.

2 5 In preference the apparatus is adapted to derive power from an internal combustion engine and preferably includes a gearing means to couple an output from the internal combustion engine to the input of the electricity generator.

In preference the apparatus includes a supporting frame adapted to be towed by 3 0 a tractor and the generator or gearing means is adapted to be connected to the power take off of the tractor.

In preference the microwave generator includes an array of spaced apart magnetrons, each of said magnetrons having a microwave outlet into said microwave cavity so that in use microwaves are directed to the ground surface, so as to provide a uniform irradiation of the upper layer of topsoil.

In preference the said microwave cavity is defined within a shielding means, said shielding means comprising a sealing chamber including a lowermost open end and sealing means at a lowermost portion of the skirts adapted for sealing contact with a ground surface, said shielding means adapted to provide a microwave cavity, impermeable to microwaves except into the ground when in contact with the ground surface.

In one form the sealing chamber comprises a rectilinear uppermost plate with a plurality of apertures therethrough providing sealed communication between said microwave cavity and said microwave outlets, a skirt depending downwardly from a periphery of the uppermost plate, said skirt being substantfially rectilinear and including four walls; a front wall and a back wall both being lateral to the direction of movement of the apparatus and two opposite side walls, said shielding means further including a roller, supported between the lowermost edge of the front wall and the ground surface and the back wall and the ground surface so as to effect a sealing therebetween, the side walls including a downwardly extending sheet, extending from the lowermost edge of both of the respective side walls to below the ground surface, and a portion of said downwardly extending sheets being in close proximity to an edge of both rollers so as to prevent leakage of microwaves between the rollers and the downwardly extending sheets.

In another form rubber flaps extend downwardly from the front and back walls of the shielding means, and together with downwardly extending sheets from the side walls provide a sealing effect between the lowermost edge of the shielding means and the ground surface, when in use.

In a further form the apparatus includes a secondary shield, surrounding the shielding means, said secondary shield including a second skirt depending from the frame member and including a second sealing means for effecting a seal between a lowermost end of the second skirt and a ground surface.

For a better understanding of the invention reference will now be made to one embodiment of the invention and the figures wherein:- FIG. 1 is a schematic layout of the functions of the apparatus, FIG 2 is a schematic plan view from above of one embodiment of the apparatus, FIG 3 is a side plan view showing the generator in broken line, FIG 4 is a view from the back of the apparatus, and 1 0 FIG 5 is a perspective view from behind the apparatus.

In one embodiment the apparatus is mounted on a frame 1, and is adapted to be towed behind a tractor. The frame of the apparatus includes three mounting points 2 for linkage with the three point linkage of the tractor for towing of the 1 5 apparatus and maintaining the apparatus at a given height. Further the apparatus includes gearing means 3 adapted to convert the rate of rotation of the Power take-off of the tractor to the speed required by a generator 4 to produce a stable prime electrical power supply. Most of the power produced by the generator is converted by transformers 5 to a suitable configuration for use by the magnetrons within a magnetron cavity 6 and other controls. Microwaves produced by the magnetrons are directed from the microwave outlets through the microwave cavity 7, and onto the ground surface 13.

A cooling fan 8 is mounted above the magnetron cavity for cooling the magnetrons. The microwave cavity is substantially rectilinear, and includes a downwardly depending skirt, having a front wall and a back wall. Sealing means are provided at a lowermost portion of the skirt and the sealing means is adapted to effect a seal between the ground surface and the skirt. In this embodiment both of the side walls have a further plate 9 (best shown in FIG 3) extending 3 0 downwardly from both side walls of the skirt of the microwave cavity. The further plate 9 thus extend under the ground surface 13 and some way into the top soil.

An elongate roller 10 is supported between a lowermost portion of the front and rear walls respectively and the ground surface. A front guard 11 and a rear guard 12 are mounted over the elongate roller at the front and rear respectively. A 3 5 portion of the further plate extends forwardly and backwardly from the front and back respectively of the further plate and the roller is mounted at either side onto the portion of the further plate 9 at the respective side, and is in close association (not shown) with the portion of the further plate, so as to provide a sealing effect at both sides of the microwave cavity.

The shielding means around the microwave cavity is made from mild steel, as are the further plates 9, and the front guard 12 and rear guard 12.

As an alternative to rollers there can be provided aluminised rubber flaps, extending from lowermost portions of the front and rear walls of the shielding means, and to a ground surface; preferably so that the rubber flaps stretch along the entire length of the front and rear walls, and being longer than the distance between the lowermost portion of the front and rear walls to the ground surface.

Thus the rubber flaps will scrape against the ground so as to provide a seal.

Further if there are problems relating to unevenness of the ground a rake can be mounted in front of the shielding means, to level the ground surface before the roller flattens it. The step of soil sterilization is usually done after soil has been prepared for seeding or planting, and thus is in a friable state, having been worked. The weight of the apparatus on the soil has a flattening effect on the soil surface providing a very good soil. The further plates on either side of the microwave cavity enter through the ground providing a seal at either side of the cavity.

A secondary shielding means can also be provided. The secondary shielding means (not illustrated) can include a sleeve depending downwardly and around the shielding means from an uppermost substantially horizontal plate extending outwardly from the shirt of the shielding means around the microwave cavity. A second sealing means can also provided at a lowermost portion of the secondary shielding means so as to effect a second seal with the ground surface. The form of the second sealing means can be the same as those discussed for the shielding means.

A variety of sensors may be mounted on the secondary shielding means. Thus as ground contact is an important factor in ensuring that microwaves do not leak, a sensor for determining that there is adequate ground contact is mounted on a lower surface of the microwave cavity. Further an interlock mechanism is preferably provided such that the magnetrons are not active when the shielding means is not in adequate contact with the ground surface. Further there is, preferably, within the secondary shielding means a microwave leak detector to determine whether microwaves have leaked beyond the shielding means.

Preferably the microwave leak detector activates an interlock preventing further microwave generation on detection of a leak.

All access doors to the power supply, and high voltage transformers and magnetron cavity are to be interlocked with the power supply, so that if any of 1 0 these are left unsecured the power supply is interrupted.

Further a detector of movement of the apparatus is interlocked so that the magnetrons do not produce microwaves if the apparatus is stationary. A temperature sensor adapted to determine the temperature of the magnetrons is 1 5 also provided. The sensor can be interlocked with the power control so that if the magnetrons become excessively hot they can be switched off while maintaining the cooling fan on.

In one form of the apparatus a microprocessor controls all of the functions with continuous data feedback from the ground, so that different applications of microwaves can be given to a particular patch of topsoil depending on its condition, e.g. soil moisture, temperature, or type of soil.

Further multiple rows of magnetrons ca, be provided to give a greater exposure to the soil of microwave energy alternatively a greater density of magnetrons could be provided. This is preferable to increasing the energy input for each individual magnetron.

An instrument panel 14 is also provided to display various function of the 3 0 apparatus, and would thus include a display of the speed of the Power take-off, the soil temperature, the moisture content of the soil, the temperature of the mnagnetrons etc.

This embodiment of the apparatus derives power from the Power take-off of a 3 5 tractor. It is envisaged that an input of 30 to 35 kilowatt is required to supply the 16 magnetron units, each of which need 1.25 kilowatt operating power. This is to be converted by the generator to a 415 Volt of ac current 3 phase power supply.

A 5% tolerance of voltage/current is allowed before the supply is cut, thereby protecting the magnetrons, which are sensitive to variations in voltage.

The 415 V ac current is transformed by two transformers, one for supplying power at 4.4 V ac at 14 amps, and the second for supplying power at 2.5 K V ac at 500 milli amps nominal and 1.6 A peak load. Thus the voltage is stepped down considerably to decrease problems with variations in the output from the generator.

The Power take-off of a tractor at relatively high revolutions is found sufficient to produce adequate power. It is found that a speed in the range of 300 540 r.p.m.

is sufficient. A change in the speed of the P.T,O. results in a change in the frequency of the power supply, however the voltage can be maintained and a 1 5 variation in frequency does not affect the operation of the magnetrons significantly. Magnetrons can adequately be powered from D.C. current as from A.C. current and thus the P.T.O. of a tractor despite possible variations in speed can be effectively harnessed for this purpose.

The power input is directed to each of 16 magnetrons, which are equally spaced apart in an array, 8 in one row, and 8 in second row over a width of approximately 2 metres. The magnetrons of the second row being staggered with respect to the magnetrons of the first row; all the magnetrons being equally spaced apart. The microwave outlet is such that in use it is 200mm above the ground surface. This is found to give a relatively even coverage of the ground surface, and adequate penetration into the upper layers of the topsoil.

The apparatus is intended for relatively slow towing speeds, such as approximately 500 meters per hour.

Claims (11)

1. An apparatus for sterilizing a layer of soil immediately beneath a soil surface, said apparatus adapted to be moved over a ground surface, and including a microwave generator said apparatus including a microwave cavity providing a microwave-impermeable passage way for microwave radiation to said soil surface, and including sealing means for inhibiting leakage of microwaves from between peripheral edges of a lowermost portion of said cavity and the soil surface and said microwave generator being adapted to 1 0 radiate microwaves into the layer of soil through the microwave cavity, so as to have a sterilizing effect on the layer of soil.

2. An apparatus as in claim 1 including an electricity generator and voltage regulator for providing electrical power of a uniform voltage to said 1 5 microwave generator.

3. An apparatus as in claim 2 adapted to be coupled to an internal combustion engine and including gearing means to couple an output from the internal combustion engine to the input of the electricity generator.

4. An apparatus as in any one of the preceding claims including a supporting frame for supporting said apparatus and said frame adapted to be towed by a driven vehicle and the generator or gearing means being adapted for connection to a power take-off of the driven.

An apparatus as in any one of the preceding claims wherein the microwave generating means includes an array of spaced apart magnetrons, each of said magnetrons having a microwave outlet into said microwave cavity so that in use microwaves are directed to the ground surface, said magnetrons being so spaced apart to provide a uniform irradiation of the layer soil.

6. An apparatus as in the preceding claim wherein microwave cavity is defined between an uppermost substantially horizontal wall having microwave outlets therethrough and a downwardly depending skirt and have at lowermost end sealing means adapted for sealing contact with the soil surface, said microwave cavity being impermeable to microwaves except into the soil when said apparatus is in contact with the soil surface. 14" L

7. An apparatus as in any one of the preceding claims wherein the microwave cavity comprises an uppermost plate with a plurality of apertures therethrough providing communication between said microwave cavity and said microwave outlets, a skirt depending downwardly from a periphery of the uppermost plate, said skirt being substantially rectilinear at a lowermost portion and including four walls; a front wall and a back wall both being lateral to the direction of movement of the apparatus and two side walls, said sealing means including a first roller, supported between the lowermost edge of the front wall and the ground surface and a second roller supported between the lowermost edge of the back wall and the ground surface so as to effect a sealing therebetween, the said walls including a downwardly extending plate, extending from the lowermost edge of both of the respective side walls to below the ground surface, and a side guard extending between each of said plates and a respective side of the rollers in close proximity to an edge of the respective roller so as to prevent leakage of microwaves between the roller and the downwardly extending sheets.

8. An apparatus as in Claim 7 wherein a first guard extends from the front wall and over the first roller so as to provide a barrier for leakage of microwaves from between the skirt and the first roller and a second guard extends from the back wall and over the second roller so as to provide a barrier for leakage of microwaves from between the skirt and the second roller.

9. An apparatus as in any one of claims 1 to 6 wherein the microwave cavity comprises an uppermost plate with a plurality of apertures therethrough providing sealed communication between said microwave cavity and said microwave outlets, a skirt depending downwardly from a periphery of the uppermost plate, said skirt being substantially rectilinear at a lowermost portion and including four walls; a front wall and a back wall both being lateral to the direction of movement of the apparatus and two side walls, said sealing means including a first flexible flap, supported between the lowermost edge of the front wall and the ground surface and a second flexible flap supported between the lowermost edge of the back wall and the ground surface so as to effect a sealing therebetween, the said walls including a downwardly extending plate, extending from the lowermost edge of both of the respective side walls to below the ground surface, and a side guard extending between 11 each of said plates and a respective said of the roller being in close proximity to an edge of the apparatus roller so as to prevent leakage of microwaves between the roller and the downwardly extending plates.

10. An apparatus as in any one of claims 6 to 9 including a secondary shield, surrounding the lowermost portion of the skirt of the microwave cavity, said secondary shield including a second downwardly depending skirt and including a second sealing means for effecting a seal between a lowermost end of the second skirt and the soil surface.

11. An apparatus substantially as hereinbefore described with reference to the illustrated embodiment. Dated this 11th day of November 1992. BRYAN ROBINSON, FRANK PERRE AND PAT PERRE By their Patent Attorneys, COLLISON CO. I