Plant husbandry – Electroculture – magnetoculture or electrocuting
Reexamination Certificate
1999-04-16
2001-05-29
Poon, Peter M. (Department: 3643)
Plant husbandry
Electroculture, magnetoculture or electrocuting
Reexamination Certificate
active
06237278
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns a method and a device for weed control by means of electricity.
For many years the use of weed poisons, in addition to purely mechanical methods, has been the dominating method for weed control. There is increasing concern that an extensive use of weed poisons may harm the environment as well as humans and animals. This concern has led to an increasing interest for alternative non-chemical methods as a complement to the traditional mechanical methods.
The concept of killing weed by means of electric energy has been used since the 1890's when “Vegetation exterminators” was patented (Sharp, A. A. 1893, Scheible, A. 1895) The technique was also developed also for weed control in the agriculture (Buret, W. E. 1928, Opp, F. W. ; Collins, W. C. 1935, Opp, F. W. 1952, Poynor, R. R. 1954). It has been further suggested for use in farming, in particular non-specific superficial treatment of the soil by moving electrodes along the ground surface and applying an alternating voltage (Laronze 1982) or constant high voltage (Krause 1975).
Equipment using electric current for pruning of blueberry bushes and dehydration of the foliage of root crops before harvest has been suggested by (Plueneke, R. H. ;Dykes, W. G. 1975, Plueneke, R. H. ;Dykes, W. G. 1977).
Thinning out of drilled plants was suggested in the 1950's by (Rainey, E. C. 1952, McCreight, N. L. 1953). Use in soil sterilizing and fertilizing has also been suggested (Keller, C. R. 1947, Opp, F. W.; Collins, W. C. 1935). Wayland et al (1975) showed that technically one can use micro waves for sterilizing soil before sowing. Weed and weed seed a few cm into the ground can be killed with microwaves having a frequency of 2450 MHz and the power 60 kW. The machine used was a 150 kW diesel driven generator that fed a microwave generator and a hydraulic system that slowly moved the equipment forward. Dipose et al. (1984) estimated that it would take between 100-1000 hours per feature to treat some types of weeds. Such long times are unavoidable. The machine radiates microwaves down into the ground to heat everything and must literally boil the weed which requires a great deal of energy. A further drawback is that also the micro flora in the soil is knocked out.
As is apparent from the above it has not yet turned out to be practical to use electricity for weed control. It is quite simply too expensive and time consuming in relation to chemical and mechanical control methods.
THE SUMMARY OF THE INVENTION
Despite the above problems the object of the invention is to provide a method for weed control based on the use of electricity. Surprisingly enough, in view of the known technique, weed control with electricity can in accordance with the invention be carried out with a very reasonable energy consumption by using short high voltage pulses with low energy content but sufficiently high for electropermeabilitation of cell membranes in growing weeds. The invention can be used for weed control in farming, horticulture gardening, forestry, parks or other suitable areas and particularly connection with sowing. The invention only damages growing seeds and plants early in their life cycle and makes it impossible for them to germinate or survive on. Dry seeds for sowing are not affected which is why the invention can be used with advantage in connection with sowing without influencing seed germination. Neither is the micro flora in the soil affected within the specified voltage span. When seeds start to grow they are very sensitive to electricity. However, when the seed has grown into a plant a considerable amount of electrical energy is necessary to harm the plant to the extent that it does not continue to grow on. In order harm ungrown seeds with electric voltage pulses or electric current, considerable amounts of electric energy is required, one must practically boil the seed.
The problem is that when the intended crop is sown, the seeds of the weeds are already in the ground and have already started to germinate. According to known techniques, one is therefore obligated to fight the weeds in order to let the intended crop come into its own. By treating the ground that is to be sown in accordance with the invention with electrical pulses with low energy, weeds that have just started to germinate can be stopped in their development. By undertaking this control simultaneously with sowing, the intended crop is given an improved chance of having time to grow before the weeds grow. Thus, by employing the use of electricity in accordance with the present invention in connection with planting and preferably simultaneously with sowing, it is possible to eliminate germinating weed seeds. Weed seeds growing later have less chance of asserting themselves since they have competition from the growing crop. Furthermore, since sowing typically has been preceded by mechanical working of the ground, pre-existing weeds already would have been eliminated. By feeding short high voltage pulses to the ground the sprouting weed can be controlled. The high voltage pulses of short duration will not cause any great damages to the weed sprouts as such. However, the amount of energy is sufficient to achieve an electropermeabilizing of the cell membranes of the sprouting weed seeds. This in turn leads to stopping growth for the damaged sprouts. Since the seeds of the intended ground crop has yet started to germinate at sowing they are not affected and sowing and weed control can be executed with the same machine without any inconvenience, on the contrary it is particularly practical to execute weed control and sowing simultaneously so that the intended crop gets the competing weed sprouts eliminated at the optimally correct time. The amount of energy that is required for the control described here is insignificant and is apparent from the following formula 1.
Formula 1
Mean power=(conductivity in the ground)×(the field strength)
2
×(degree of modulation)/(Density) (W/kg)
Conductivity=0.2 siemens
Field strength=300 000 volt/m
degree of modulation=1/10 000
density 1500 kg/m
3
The momentary power in the pulse is very high, for instance 12 MW/kg but since the pulse is of very short duration (typically 100 microseconds long) and is applied once a second the mean power is considerably lower, that is 12 kW/kg. In practice a capacitor battery charged that is discharged very quickly and deliver the desired high voltage pulse. Alternatively, alternating voltage is used that can be transformed to high voltage.
The treatment of plant cells with these high voltage pulses primarily influences protoplasm dependent on the barrier that is constituted by the cell wall. With rectangular pulses the optimal amplitude of the field strength is between 100-300 kV/m with a duration of (10-100 micro seconds). With exponentially declining pulses the field strength is weaker (25-75 kV/m) and the duration of the pulse longer (1000-20 000 microseconds).
There are examples of experiments with intact plant cells of for instance rice that shows that the cell wall is not an absolute obstacle to electroporation (Morikawa et al 1986; Dekeyser et al.,1990). The invention is based on one using an electric field strength high enough so that the cell membranes are destroyed or punctured and the cell dies as a result of this. The earth bed is treated with pulses of short duration (0,1-1 millisseconds) with the field strength 150-300 kV/m (1500 3000 V/cm). These high field pulses have has a selective destructive effect on germinating weed seeds while dry seeds for sowing are not influenced. In order to effect the bacterial flora in the ground, higher field strengths and longer pulses are necessary. However, larger animals as maggots or noxious; insects may be affected.
This new technique has been evaluated with white mustard (Sinapsis alba, var. Emergo) simulating weed with high germination (87 %). The white mustard was cultivated in fertilized peat earth (70% earth, 30% Perlite) in plastic containers (5×11×
Henriksson Pär
Mattsson Berit
Nybrant Tomas
Persson Bertil
Gellner Jeffrey
Hayes Soloway Hennessey Grossman & Hage PC
Poon Peter M.
Zero Weed AB
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