JP7738291B2 - Weeding and weed control equipment - Google Patents

Description

The present invention relates to a weeding and weed control machine that uses electrical stimulation to control weeds.

Labor-saving and cost-effective weed control is required in all areas, including agriculture and construction sites. Commonly known weed control methods include chemical control using pesticides and physical control such as mowing with brush cutters. The former, chemical control, poses concerns about the impact on ecosystems and the risk of causing various environmental problems, such as scattering to nearby areas and impacting water systems through underground runoff. There are also concerns about the effects on humans from inhaling the ingredients contained in pesticides. Furthermore, the latter, physical control, requires more frequent weeding, as weeds quickly regrow from the roots remaining underground even after the stems and leaves above ground are cut, resulting in increased labor costs and posing challenges such as the risk of heatstroke when working in extreme heat, as well as health damage to workers due to the vibrations and noise of brush cutters.

In addition to the chemical and physical control methods mentioned above, electrical control methods have also been developed in recent years, in which high voltage is discharged or applied to weeds. This electrical control method involves applying a high voltage between electrodes and applying the discharged current to the weeds to electrically stimulate them, or by directly contacting the weeds with electrodes to which a high voltage has been applied, thereby destroying their cells and tissues and causing them to wither and die.

As an example of such an electrical control method, Patent Document 1 below discloses an electric weeding device equipped with a high-voltage generator, which is a discharge-based weeding device that simultaneously uses the discharge or application of high voltage or static electricity to wither and kill plants, and to cut or crush them. This electric weeding device has an upper cutting blade connected to a positive electrode from the high-voltage generator, and a lower cutting blade connected to a negative electrode from the high-voltage generator. When weeds come into contact with the cutting blades and are cut, a spark discharge occurs, and the weeds exposed to this discharge have their root, stem, and leaf cells destroyed, resulting in their being crushed and removed.

Patent Document 2 below discloses a weeding machine that includes a vehicle body, a traveling device that supports the vehicle body so that it can travel, and a discharge device that is mounted below the vehicle body and is capable of discharging electricity toward plants growing on the ground that are the target for removal. The discharge device has an insulating outer shell and a discharge unit that is covered by the outer shell and discharges electricity toward the ground. The discharge unit is composed of an application electrode that faces downward relative to the conductive axis of the outer shell and multiple plate-shaped power receiving units attached to the inside surface of the outer shell. When a discharge occurs in the gap between the tip of the application electrode and the power receiving unit, discharge products resulting from the discharge pass through through holes that are mounted between the power receiving units of the outer shell and exit the outer shell.

Japanese Patent Application Laid-Open No. 2002-186324 Japanese Patent Application Laid-Open No. 2020-80732

However, the weeding device disclosed in Patent Document 1 above poses the risk of electric shock due to electrical leakage, making it impossible to ensure the safety of the operator. Furthermore, while the discharge device attached to the brush cutter is expected to reduce the frequency of weeding, it still requires a person to move around and perform the weeding work with the brush cutter, as is the case with conventional brush cutters, so it does not result in labor savings and requires high labor costs.

Furthermore, with the weeding machine disclosed in Patent Document 2, when discharge products resulting from discharge occurring in the gap between the application electrode and the power receiving part are discharged onto weeds, only those that pass through the through-holes and emerge outside the shell act on the weeds. As a result, the amount of discharge that acts on the weeds is small, making it impossible to effectively electrically stimulate many weeds, and there are also problems with consuming a large amount of power to ensure a large amount of discharge.

The primary objective of this invention is to provide an environmentally friendly weeding and weed prevention machine that is highly effective at weeding and weed control, reduces labor required, and maintains its effectiveness over the long term.

In order to solve the above problems, the present invention according to claim 1 provides a vehicle that can travel, and a pair of electrodes that are disposed on a surface of the vehicle that faces the ground in a state where they protrude toward the ground and are disposed opposite each other with a predetermined distance between them,
The present invention provides a weeding/weed-prevention machine characterized in that an electrical stimulus is given to a plant located between the pair of electrodes by the electrical action generated between the pair of electrodes.

The invention described in claim 1 above is a first embodiment of the weeding and weed control machine of the present invention. A pair of electrodes is disposed facing each other on a mobile vehicle, and an electrical action is generated between the electrodes, thereby providing an electrical stimulus to plants located between the electrodes. This weed control using a pair of electrodes mounted on a mobile vehicle reduces labor. Furthermore, plants exposed to the electrical stimulus undergo irreversible cell perforation, causing the cellular contents to leak out and ensure death. The electrical stimulus reaches the roots of the plants, damaging them as well, resulting in a long-lasting weed-killing effect. Furthermore, the electrical action generated between the pair of electrodes also affects seeds held by the plants and seeds spilled onto the ground, thereby suppressing the germination rate of these seeds, thereby providing a weed-control effect. This type of weed control using electrical stimulation is environmentally friendly, eliminating the risk of pesticides scattering or leaking into groundwater. The electrical action can be any one or a combination of two or more of the following: an electric field generated between a pair of electrodes; a current flowing from one electrode to the other through at least the plant when the plant comes into contact with the electrode; and an electric discharge occurring in the gap between the electrode and the plant.

As a second aspect of the present invention, there is provided a weeding/weed prevention machine as described in claim 1, in which the pair of electrodes extend along the direction of travel of the vehicle and consist of flat plates arranged parallel to and spaced apart in a direction perpendicular to the direction of travel.

In the invention described in claim 2 above, a specific embodiment of the pair of electrodes is configured as parallel flat plates that extend along the direction of vehicle travel and are spaced apart in a direction perpendicular to this. This creates a three-dimensional electric field between these parallel flat plates, and current flows to plants through plants and soil that come into contact with the electrodes, ensuring that many plants are electrically stimulated, further improving the effectiveness of weed control and weed prevention.

According to a third aspect of the present invention, the vehicle includes a vehicle body and a running body,
There is provided a weeding/weed prevention machine according to claim 1 or 2, wherein the pair of electrodes is provided on a lower part of the vehicle body.

In the invention described in claim 3 above, the pair of electrodes is provided under the vehicle body, reducing the risk of electric shock and improving work safety.

The present invention provides a weeding/weed prevention tool according to any one of claims 1 to 3, in which the electric field strength between the pair of electrodes is 1.1 kV/cm or more.

In the invention described in claim 4 above, an electric field of a predetermined field strength or greater is applied between the pair of electrodes to apply a strong electrical stimulus to the plant, causing irreversible cell perforation and ensuring the plant's death.

According to a fifth aspect of the present invention, there is provided a weeding and weed prevention machine according to any one of the first to fourth aspects, wherein the vehicle is self-propelled.

In the invention described in claim 5 above, since the vehicle is self-propelled, it is possible to remove weeds automatically, thereby further reducing the labor required for weed control work.

As explained in detail above, the present invention makes it possible to provide an environmentally friendly weeding and weed prevention machine that is highly effective in weeding and weed control, reduces labor required, and maintains its effectiveness over the long term.

1 is a side view showing a weeding/weed prevention machine 1 according to a first embodiment. FIG. FIG. 2 is a view taken along the line II-II in FIG. 1. FIG. 10 is a side view of the weeding and weed prevention machine 1 according to a modified example. FIG. 1 is a schematic diagram of a PFN type single pulse generating circuit. FIG. 1 is a schematic diagram of the experimental setup. 10 is a graph showing the relationship between the total weight of lettuce leaves and the applied pulse electric field strength. 1 is a graph showing the percentage increase or decrease in the total weight of lettuce leaves. FIG. 10 is a cross-sectional view showing a weeding/weed prevention machine 1 according to a second reference embodiment. 9 is a view taken along the line IX-IX in FIG. 8. FIG. 1 is a schematic diagram of an experimental device for current flow experiment 1. FIG. 1 is a schematic diagram (part 1) of the experimental apparatus for current flow experiment 2. FIG. 2 is a schematic diagram (part 2) of the experimental apparatus for current flow experiment 2. 1 is a cross-sectional view showing a weeding/weed prevention machine 1 equipped with a sprinkler device 20. FIG. 1 is a cross-sectional view showing a weeding/weed prevention machine 1 towed by or automatically following a water sprinkler vehicle 21. FIG. 1 is a cross-sectional view showing a weeding/weed prevention machine 1 equipped with a rotary power receiving unit 11. FIG.

Embodiments of the present invention will be described in detail below with reference to the drawings.

[First embodiment]
As shown in Figures 1 and 2, a weeding and weed prevention machine 1 according to a first embodiment of the present invention comprises a drivable vehicle 2 and a pair of electrodes 3, 3 that are arranged on the surface of the vehicle 2 facing the ground in a state where they protrude toward the ground and are arranged opposite each other with a predetermined distance between them, and the electrical action generated between the pair of electrodes 3, 3 provides an electrical stimulus to a plant 4 located between the pair of electrodes 3, 3.

The vehicle 2 comprises a body 5 and a running frame 6 that supports the body 5 so that it can move. The vehicle 2 is preferably remotely controlled or automatically self-propelled to reduce the labor required for weeding and weed control work, but it may also be driven by a driver in a driver's seat provided in the body 5, or towed by or automatically followed by another vehicle. In this way, weeds can be controlled using the pair of electrodes 3, 3 provided on the mobile vehicle 2, which significantly reduces the labor required compared to weeding performed by a person moving around with a brush cutter.

The vehicle body 5 is equipped with a drive device such as an engine or motor that drives the running body 6, as well as a power supply device (battery) that supplies electricity to the electrodes 3 and the drive device. By providing a detachable power supply device, a fully charged power supply device can be used to control weeds over a wide area for an extended period of time.

The running body 6 may be a tire-and-wheel system consisting of at least front and rear wheels provided at the front and rear of the vehicle body 5, as in the illustrated example, or it may be a caterpillar system.

The pair of electrodes 3, 3 is provided on the lower part of the vehicle body 5 and is positioned so as to protrude from the underside of the vehicle body 5 toward the ground. The pair of electrodes 3, 3 extend along the direction of travel of the vehicle 2 and are composed of parallel flat plates spaced apart in the width direction of the vehicle 2, which is perpendicular to this. The electrode 3 is formed in a flat plate shape with a predetermined length in the direction of travel of the vehicle 2 and a predetermined height in the height direction, so that almost the entire surface of this flat plate exerts an electrical effect. The pair of electrodes 3, 3 are provided on the left and right sides of the vehicle 2 at a distance, so that as the vehicle 2 travels, plants 4 pass between these electrodes 3, 3. As shown in Figure 1, because the electrode 3 has a predetermined length in the direction of travel of the vehicle 2, a predetermined section along the direction of travel becomes an application section E in which an electrical effect is exerted.

The electrical action can be any one or a combination of two or more of the following: an electric field generated between the pair of electrodes 3, 3; a current flowing from one electrode 3 to the other electrode 3 through at least the plant 4 in contact with the electrode 3; and an electric discharge occurring in the gap between the electrode 3 and the plant 4.

The length of the electrode 3 in the direction of vehicle travel should be 5 to 50 cm, preferably 10 to 30 cm. Its height should be 3 to 40 cm, preferably 5 to 20 cm.

A plant 4 passing between the pair of electrodes 3, 3 is electrically stimulated by the electrical action generated between these electrodes 3, 3. When the electrical action is an electric field, the high electric field strength causes irreversible cell perforation, resulting in the leakage of cell contents and cell destruction, which hinders nutrient absorption and eventually leads to death. The electrical stimulation applied to the leaves and stems of the plant 4 exposed above ground reaches the roots underground and causes significant damage to the roots, resulting in a long-lasting herbicidal effect. Furthermore, the electrical action generated between the pair of electrodes 3, 3 also acts on seeds held by the plant 4 and seeds that have fallen to the ground, thereby suppressing the germination rate of these seeds and thereby achieving a herbicidal effect. Weed control using such electrical stimulation is environmentally friendly compared to chemical control methods, as it does not pose the risk of pesticides scattering or flowing into groundwater.

As described in the non-patent literature detailed below, it has been confirmed that applying a certain electric field to plants promotes their growth through the electroporation effect. However, electric field strengths higher than this are too strong a stimulus for plants, causing irreversible cell perforation, which has adverse effects on plants, resulting in the leakage of cellular contents. Based on the experimental results described in the non-patent literature below, the electric field strength that causes irreversible cell destruction in plants should be 1.1 kV/cm or greater, preferably greater than 1.5 kV/cm.

The pair of electrodes 3, 3 are each connected by an electrical cable to a power supply unit (not shown) mounted on the vehicle body 5, with one electrode 3 being positively charged and the other electrode being negatively charged, and a high voltage being applied.

The lower end of the electrode 3 may be in contact with the ground or may be spaced above the ground. In other words, the lower end of the electrode 3 may be at approximately the same height as the lower end of the wheel, or may be higher. Alternatively, as shown in Figure 3, the lower end of the electrode 3 may be positioned below the lower end of the wheel so that it is buried in the ground. It is preferable to position the lower end of the electrode 3 as close to the ground as possible, and preferably so that the lower end of the electrode 3 is buried in the ground, as this makes it easier to apply an electric field not only to the stems and leaves of plants but also to their roots.

In the side view of the vehicle 2 shown in Figure 1, the lower edge of the electrode 3 is shown as a straight line that is approximately parallel to the ground. However, as shown in Figures 3(B) and (C), it is preferable to form the electrode 3 in an arc shape that bulges out in the center toward the ground, or in an inclined shape that protrudes downward more toward the rear of the vehicle than toward the front of the vehicle, as this makes it easier for the electrode 3 to overcome obstacles such as stones and allows the vehicle 2 to travel smoothly. In addition, the portion of the lower edge that is arc-shaped or inclined and closest to the ground is partially buried in the ground, making it easier to apply electrical effects such as electric fields to plant roots.

Electroporation, a technique for perforating cells using a pulsed electric field, has been known for some time and has recently begun to be applied to the agricultural field. In a non-patent document (Wang Douyan, Goto Takahiro, Yoshida Takafumi, Namihira Takao, Akiyama Hidenori, Fujiwara Toshiyuki, Sato Daigo; "Lettuce Growth Control Using Pulsed Electric Fields," Institute of Electrical Engineers of Japan Pulsed Power Study Group Materials, PPT-12, March 2012, pp. 13-16), the inventors of the present application reported the results of an experiment conducted to examine the relationship between the strength of the applied pulsed electric field and lettuce yield, focusing on hydroponic lettuce, a major variety cultivated in plant factories, as the target crop for application of a pulsed electric field, with the aim of controlling plant growth by applying a pulsed electric field to the roots of the plant, thereby shortening the number of days required for agricultural crop cultivation, which is one solution for promoting the widespread use of plant factories. The following is an outline of the experiment.

1. Experimental method (sample to which pulse electric field is applied)
In the experiment, a pulsed electric field was applied to the roots of hydroponic lettuce (variety: Early Impulse). The lettuce seeds were sown in nursery pots filled with compost and grown in the pots until planting time (approximately 20 days after sowing). From planting time onward, the nursery pots were immersed in liquid fertilizer, allowing the liquid fertilizer to circulate. The nursery pots were made of thin resin, with multiple slits spaced around the periphery on the lower side. The liquid fertilizer was absorbed through these slits, and the growing roots extended outward. The lettuce leaves were harvested approximately 40 days after sowing.

For the experiment, the plants were transferred to an incubator (M-230F, manufactured by Taitec Corporation) at the time of planting and cultured for approximately 20 days until harvest. During this time, a pulsed electric field application experiment was conducted. Culture conditions were a temperature of 20-21°C, humidity of 30-95%, fluorescent lighting 24 hours a day, and illuminance of 6,800-10,000 lux. Within the incubator, seedling pots were placed in plastic trays soaked in liquid fertilizer, and a constant amount of liquid fertilizer was maintained by adding more liquid fertilizer to make up for the loss caused by evaporation within the incubator.

<Pulse electric field generator>
A pulse-forming network (PFN) single-pulse generator circuit was used to generate the pulsed electric field. A schematic diagram is shown in Figure 4. The PFN was connected in seven stages, with an inductance of 2 μH and a capacitance of 2.7 nF for each stage. The theoretical output pulse width was 400 ns, and the power supply characteristic impedance was 10 Ω. The characteristic impedance was calculated from the conductivity (approximately 1 ms/cm) of the liquid fertilizer used for hydroponic lettuce cultivation and the electrode shape for applying the electric field. A matched load of 10 Ω was connected to the PFN input terminal to absorb the reflected wave generated at the load terminal on the input side, resulting in a single-pulse output.

A DC high-voltage power supply (PS/EW40R15.0-10, manufactured by GLASSMAN HIGH VOLTAGE) was used to charge the PFN. In addition, a negative pulse voltage was applied to the load to prevent discharge between the electrodes.

The voltage waveform applied between the electrodes was measured using a high-voltage probe (P6015A-R3, Tektronix), and the current to the load was measured using a current probe (Pearson current monitor, Model 110, Pearson Electronics) and an oscilloscope (TDS3054B, Tektronix).

To form the reactor for applying a pulsed electric field to lettuce roots, stainless steel parallel plate electrodes (80 mm diameter, disk-shaped) were fixed to the opposing walls of an acrylic container. To vary the applied pulsed electric field strength, multiple acrylic containers of different lengths were created, and the parallel plate electrodes were attached to the container appropriate for the desired electric field strength.

<Method for applying a pulsed electric field and method for evaluating the growth of lettuce>
The pulsed electric field application began around the 20th day before the planting period and was applied once daily in the morning until harvest. The pulsed electric field application procedure involved first filling the reactor with fresh liquid fertilizer, then placing the lettuce plants removed from the incubator between parallel plate electrodes so that the entire seedling pot was submerged in the liquid fertilizer (see Figure 5). After applying the pulsed electric field to the lettuce roots, the seedling pot was removed from the reactor and returned to the incubator. The liquid fertilizer used during the electric field application in the reactor was discarded and not used for lettuce cultivation.

Based on the findings from the preliminary tests, the frequency of the pulsed electric field applied to the lettuce roots was determined to be 1 Hz, the number of applications was determined to be 100, and the electric field strength was varied from 0.2 to 2.0 kV/cm. Taking into consideration the biological balance of the lettuce itself, three samples were used for each parameter. In addition, the control sample was treated in the same way as the pulsed electric field-applied sample, and the electric field strength was set to 0.0 kV/cm (no electric field applied).

To evaluate growth, the total weight of harvested lettuce leaves was compared between samples for each electric field application parameter and a control sample. Furthermore, at the time of harvest, lettuce leaves were cut to the same height as the top edge of the seedling pot, and the total weight of the leaves was measured using an electronic balance (PL3002, Mettler Toledo). To examine reproducibility, the experiment was conducted three times, and the average value was evaluated.

2. Experimental Results Figure 6 shows the dependence of lettuce leaf weight on the applied pulsed electric field strength at harvest. Table 1 and Figure 7 show the percentage increase or decrease in the average lettuce leaf weight at each electric field strength compared to the control, with the control set at 100%. Figures 6, 7, and Table 1 clearly demonstrate that lettuce growth can be controlled by applying a pulsed electric field to the lettuce roots. Furthermore, there is an appropriate electric field strength to achieve growth promotion, and applying an electric field that is too strong can inhibit growth. Under the experimental conditions of this study (pulse duration 400 ns, 1 Hz, 100 pulses applied once daily after planting), the appropriate electric field strength for promoting lettuce leaf growth was 0.5 to 1.0 kV/cm, while a strong electric field of 2.0 kV/cm or higher inhibited leaf growth. Furthermore, at 0.4 kV/cm, the greatest growth promotion effect was observed, resulting in an approximately 20% increase in production compared to when no pulsed electric field was applied.

Furthermore, at the time of harvest, the lettuce roots of the plants exposed to 0.4 kV/cm, which had the greatest growth-promoting effect, were thicker and longer, and had a higher density of root hairs, compared to the control. On the other hand, the plants exposed to 2.0 kV/cm, which showed growth inhibition, had roots that were less developed than the control plants, and the tips of the roots were brittle and crumbled when touched with the fingers.

As shown in Table 1 and Figure 7, the electric field strength at which the total weight of lettuce leaves decreases compared to the control plant is approximately 1.1 kV/cm or higher, and at electric field strengths above 1.5 kV/cm, the reduction rate is particularly significant, exceeding 20%.

[ Reference second form example]
8 and 9 , a weeding and weed control machine 1 according to a second reference embodiment of the present invention includes a travellable vehicle 2, an application electrode 10 arranged on the surface of the vehicle 2 facing the ground, and a power receiving unit 11 that is provided on the vehicle 2 and has a grounded tip, and when a plant 4 comes into contact with the application electrode 10, a current flows through a closed circuit from at least the application electrode 10 to the plant 4 to the power receiving unit 11, thereby providing an electrical stimulus to the plant 4 that is in contact with the application electrode 10. The path along which the current flows is application electrode 10 → plant 4 → power receiving unit 11 when the plant 4 is short-circuited between the application electrode 10 and the power receiving unit 11, and is application electrode 10 → plant 4 → soil → power receiving unit 11 when the plant 4 comes into contact with the application electrode 10 and the power receiving unit 11 is grounded at a position separated from the plant 4.

The application electrode 10 consists of one or more linear or rod-shaped members, and is provided on the underside of the vehicle body 5 in a state where it protrudes downward, or in a state where it is stretched approximately parallel to the underside of the vehicle body 5 at a distance below the underside. Specifically, it is preferable to use a wire or a linear material such as a wire so that it deforms appropriately when a plant 4 passes over it and then naturally returns to its original position after the plant passes over it. When the application electrode 10 is arranged in a state where it protrudes downward, its upper end is fixed to the vehicle body 5 and its lower end is a free end that hangs down toward the ground, and the lower end does not touch the ground but is arranged a predetermined distance above the ground.

The application electrodes 10 are arranged in multiple numbers, preferably 2 to 10, at predetermined intervals across the width of the vehicle 2. In the example shown in Figure 9, five application electrodes 10 are arranged between the left and right wheels 6. By arranging multiple application electrodes 10 across the width, the chances of the application electrodes 10 coming into contact with the plants 4 increase, making it easier for current to flow through the plants 4.

The power receiving unit 11 is made of a conductive metal material, preferably a chain, wire, rod, or plate. Alternatively, as described in the later section of Electrical Conduction Experiment 2, a rotating roller or caterpillar may also be used. One end of the power receiving unit 11 is attached to the body 5 of the vehicle 2, and the other end is positioned so that it is in contact with the ground. As a result, the vehicle 2 always travels while dragging the other end of the power receiving unit 11. The other end of the power receiving unit 11 may be positioned so that it is in contact with the ground, or so that it is buried underground.

The application electrode 10 and the power receiving unit 11 are preferably arranged so that the application electrode 10 is located at the front of the vehicle 2 in the direction of travel, and the power receiving unit 11 is located behind it. The application electrode 10 and the power receiving unit 11 may also be arranged side by side in a direction perpendicular to the direction of travel of the vehicle (the vehicle width direction).

[Electrical Experiment 1]
An experiment on passing electricity through plants was conducted using an experimental device simulating the above-mentioned weeding/weed prevention machine 1. This experiment on passing electricity through plants assumed a case in which a plant comes into direct contact with one of two electrodes, causing a current to flow from this electrode through the plant and soil to the other electrode, thereby electrically stimulating the plant. In the following explanation, based on the weeding/weed prevention machine 1 according to the second embodiment, the one electrode is referred to as the applying electrode 10 and the other electrode as the power receiving unit 11. However, the same effect is achieved when a current flows from one electrode 3 through a plant 4 and soil to the other electrode 3 in the weeding/weed prevention machine 1 according to the first embodiment.

As shown in Figure 10, the experimental equipment consisted of a cultivation pot containing three plants 4 (sorghum), a horizontally stretched linear application electrode 10, a power receiving unit 11 inserted into the soil from the bottom of the cultivation pot, and a power supply unit that generates pulsed power. The experimental conditions were a power output of 20 kV (open load) and a pulse frequency of 1 kpps. The height of the application electrode 10 relative to the plants 4 was set to two different heights: 65 mm and 30 mm above the soil surface. The experimental method involved applying a current to the application electrode 10 for approximately one minute while it was in contact with the plants 4, and observing the state of the plants 4. This was performed on two of the three plants in the same cultivation pot, and then the plants were continuously cultivated in an incubator for one week, during which the state of the plants 4 was observed.

As a result, after applying electricity, the plant 4 broke at the point where it had been in contact with the application electrode 10, and black scorch was observed at the broken area. Partway through the period when electricity was being applied, discharge was confirmed visually from the point of contact between the application electrode 10 and the plant 4. Approximately one week later, two of the plants 4 that had been applied electricity were confirmed to have withered and died visually, and some of their roots had become assimilated with the soil and could not be recovered, but the one plant 4 that had not been applied electricity continued to grow. The above phenomenon was the same whether the height of the application electrode 10 was 65 mm or 30 mm.

[Electrical experiment 2]
An experiment on passing electricity through plants was conducted using an experimental device simulating the above-mentioned weeding/weed prevention machine 1. This experiment 2 assumed a case in which a plant comes into direct contact with one of two electrodes, causing a current to flow from this electrode through the plant and soil to the other electrode, thereby electrically stimulating the plant. In the following explanation, based on the weeding/weed prevention machine 1 according to the second reference embodiment, the one electrode is referred to as the applying electrode 10 and the other electrode as the power receiving unit 11. However, the same effect is achieved when a current flows from one electrode 3 through a plant 4 and soil to the other electrode 3 in the weeding/weed prevention machine 1 according to the first embodiment.

The experimental apparatus consists of a cultivation pot containing one plant 4 (sorghum), a horizontally stretched linear application electrode 10, a power receiving unit 11 installed at a predetermined position depending on the experimental conditions, and a power supply unit that generates pulsed power.

As a preliminary experiment, a current-carrying experiment was conducted using Pattern 1-1 shown in Figure 11(A) and Pattern 1-2 shown in Figure 11(B). In Pattern 1-1, the power receiving unit 11, a metal rod, was inserted vertically into the soil to a depth of 30 mm from its tip, a horizontal distance L of 30 mm from the application electrode 10. The load resistance was small, approximately 3 kΩ. In Pattern 1-2, the power receiving unit 11, a metal rod, was placed in the air outside the cultivation pot, a horizontal distance L of 60 mm from the application electrode 10. The load resistance was significantly higher than that of Pattern 1-1, exceeding several MΩ. The experimental conditions were a power supply output of 20 kV (open load) and a pulse frequency of 1 kpps. The height of the application electrode 10 relative to the plant 4 was 15 mm above the soil surface. As a result, in pattern 1-1, current flowed through a closed circuit from the application electrode 10 → plant 4 → soil → power receiving unit 11, and discharge was visually confirmed from the contact point between the application electrode 10 and plant 4 partway through the current-carrying period, and after a certain period of time (several days), the plant 4 died. On the other hand, in pattern 1-2, no current flowed (or even if it did, it was below the detection sensitivity of the measuring device), and the plant 4 continued to grow. From these results, it is clear that to ensure the plant dies, a larger current needs to be passed through it.

In this experiment, plant 4 (sorghum) was grown in pots in soil that was sufficiently moist, so the closed circuit formed between the power supply and the load had a low resistance. On the other hand, in actual grassland with overgrown weeds, the resistance increases depending on the moisture content of the soil, the distance between the application electrode 10 and the power receiving unit 11, and the ground contact area of the power receiving unit 11, and if this resistance becomes excessive, a closed loop like pattern 1-2 above can be expected. Therefore, it is important to devise ways to allow a larger current to flow in grassland.

To allow a larger current to flow, an experiment was conducted to confirm the effects of watering. In the experiment, the resistance of the earth was measured and compared before and after watering the grass. An insulation resistance meter was used as the measuring instrument, and the tips of the test leads on the earth side and lead side were inserted vertically into the soil, 10 cm apart horizontally. Resistance was measured before watering and after watering at approximately 8 L/ ^m2 , and the resistance, which was 14 kΩ before watering, dropped to 5 kΩ after watering. This confirmed that watering can reduce earth resistance, allowing a larger current to flow.

Next, to obtain a larger current, a current-carrying experiment was conducted by varying the distance L between the applying electrode 10 and the power receiving unit 11 and the ground contact area A of the power receiving unit 11. The experimental apparatus is shown in Figure 12. The power receiving unit 11 may be any metal body with a tip, preferably a flat plate. In this experiment, a crimp terminal with a ring-shaped tip was used. The horizontal distance between the power receiving unit 11 and the applying electrode 10 was L. When the power receiving unit 11 was inserted into the soil (as shown in the example), both the front and back surfaces of the crimp terminal came into contact with the soil. When the power receiving unit 11 was in contact with the soil surface, the contact surface with the soil was one side of the crimp terminal. Therefore, if the ground contact area A when the power receiving unit 11 was in contact with the soil surface was 1, the ground contact area A when the power receiving unit 11 was inserted into the soil was 2. The experimental conditions were a power supply output of 20 kV (open load) and a pulse frequency of 1 kpps. As shown in Table 2, current experiments were conducted for patterns 2-1 to 2-3, which varied the height H from the soil surface to the application electrode 10, the horizontal distance L from the application electrode 10 to the power receiving part 11, and the proportion of the ground contact area A of the power receiving part 11. The applied voltage for pattern 2-1 was 10 kV and 16 A, while the applied voltage for patterns 2-2 and 2-3 was 6 to 7 kV and 10 A.

For comparison with these electrically treated plants, we also prepared plants treated with a commercially available herbicide (BASF Japan, BASTA Liquid). The herbicide was applied by dripping 10 ml of a 1:100 diluted solution evenly onto the surface of the above-ground parts of the plants.

As a result, herbicide-treated plants began to wilt one day after treatment, and by the fifth day, the wilting began mainly at the area where the solution was dripped. All electrically treated plants began to wilt by the second day after treatment, and by the fifth day, the wilting began mainly in the above-ground parts below the wire electrode contact point. In both treatments, the above-ground parts had wilted by the seventh to tenth day. For the above-ground parts of Plant 4, electrically treated plants showed the same effect as herbicide-treated plants. For the underground parts of Plant 4, electrically treated plants became so brittle that they were difficult to separate from the soil, while herbicide-treated plants thinned but maintained their shape. It is likely that the shape of the underground parts (roots) was maintained because the herbicide used in this experiment contained ingredients that primarily kill the above-ground parts of plants. In any case, while herbicides have a partial weed-killing effect, electrical treatment is effective in killing both above-ground and underground parts by creating a closed loop current circuit (allowing current to flow through the plant's roots as well). Furthermore, this tendency was more pronounced in patterns 2-2 and 2-3, in which the distance L between the applying electrode 10 and the power receiving portion 11 was reduced and the ground contact area A of the power receiving portion 11 was increased, than in pattern 2-1.

From the above experiments, it was found that in order to kill plants through electrical treatment (pulsed power application treatment), it is desirable to pass a larger current by reducing the resistance value (impedance) of the soil as much as possible in the closed circuit formed by the application electrode 10 → plant 4 → soil → power receiving unit 11.

The above experiments have made it clear that the following three methods are effective for reducing the resistance value (impedance) of the soil.
(1) Watering the soil
(2) The horizontal distance between the applying electrode 10 and the power receiving part 11 is kept as short as possible.
(3) The contact area of the power receiving unit 11 is made as large as possible. Below, specific examples of embodiments in which the above three items are applied to the weeding/weed prevention machine 1 according to the present invention will be illustrated.

(1) Watering the Soil In order to reduce the resistance value of the soil, it is preferable to water the soil before applying an electrical stimulus to the plants 4 with the weeding/weed prevention machine 1 according to the present invention. The timing of watering may be any time before the application electrode 10 comes into contact with the plants 4 and a current flows through the plants 4, but it is preferable to water the soil when it is sufficiently moist.

Watering the soil can be done by pre-spraying the area to be weeded or prevented with a hose or a sprinkler truck. Furthermore, to allow a larger current to flow through the plants 4 by applying electricity to the water sprinkled on the soil before it penetrates deep into the ground, a sprinkler device 20 may be attached to the front of the weeding/prevention machine 1 as shown in Figure 13, or the weeding/prevention machine 1 may be towed by or automatically follow a sprinkler truck 21 as shown in Figure 14.

(2) Keep the horizontal distance between the application electrode 10 and the power receiving unit 11 as short as possible In order to reduce the soil resistance, it is preferable to install the application electrode 10 and the power receiving unit 11 close to each other with a horizontal distance that does not cause an electrical short circuit between them. For this reason, it is preferable to install both the application electrode 10 and the power receiving unit 11 together in a specific location such as the rear or front of the vehicle body 5, and multiple sets of application electrodes 10 and power receiving units 11 installed close to each other may be installed on the vehicle body 5.

(3) Maximizing the contact area of the power receiving unit 11 To increase the contact area between the power receiving unit 11 and the ground, it is possible to provide multiple power receiving units 11. For example, multiple power receiving units 11 can be connected in parallel to one application electrode 10. This makes it easier for the current applied by the application electrode 10 to flow from the soil through the plants 4 to the multiple power receiving units 11.

However, if multiple power receiving units 11 grounded to the ground are provided in this way, contact resistance with the ground may increase the power required to move the weeding/weed prevention tool 1, necessitating the need to increase the size of the power unit. For this reason, to increase the contact area of the power receiving units 11 while reducing contact resistance with the ground, it is possible to use rotating rollers or caterpillars as the power receiving units 11, as shown in Figure 15.

1...Weeding/weed control machine, 2...Vehicle, 3...Electrode, 4...Plant, 5...Vehicle body, 6...Traveling body, 10...Applying electrode, 11...Power receiving unit

Claims (5)

The vehicle comprises a pair of electrodes disposed on a surface of the vehicle facing the ground in a state of protruding toward the ground and disposed opposite each other with a predetermined distance therebetween,
A weeding/weed prevention machine characterized in that an electrical action generated between the pair of electrodes gives an electrical stimulus to plants located between the pair of electrodes. The weeding and weed prevention machine according to claim 1, wherein the pair of electrodes consists of parallel flat plates extending along the direction of travel of the vehicle and spaced apart in a direction perpendicular to this. The vehicle comprises a vehicle body and a running body,
3. The weeding/weed prevention machine according to claim 1, wherein the pair of electrodes is provided on a lower part of the vehicle body. A weeding/weed prevention tool according to any one of claims 1 to 3, wherein the electric field strength between the pair of electrodes is 1.1 kV/cm or more. 5. The weeding and weed prevention machine according to claim 1 , wherein the vehicle is self-propelled.