By Takao Furuno
In 2016, after a long period of trial and error, I quite by chance tried out a “vibrating weeding broom” for weed control that uses a rake with thin, spring steel wires and was able to carry out continuous (down the row) early interplant weeding without damaging the crop.The weeding was successful using the vibrating weeding broom (VWB), and I named it hawking, after the Japanese-style broom called a hawki.
Crops (rice, wheat and other cereal grains, soybeans, maize and vegetables) are often planted in rows. The space between the rows is known as inter-row space. The spaces in between the crop plants in a row are called interplant spaces (see Figure 1).
Inter-row weeding is known as intertillage weeding. Since there are no crops growing in this space, weeding can be carried out quickly by moving forward or backward continuously with a hoe or other hand tool, or a machine.
On the other hand, in the interplant spaces the weeds and the crops are close to one another, so it would seem to be difficult to eliminate only the weeds by moving forward continuously with a machine without harming the crop.
For nearly 40 years as an organic farmer I was convinced that mechanization of interplant space weeding cannot be easily done and continued to weed between the plants using my hands or a triangular hoe. There are probably many farmers around the world who think and do the same.
Handmade Tool for Weed Control
When I talk about the VWB, someone always asks, “Where can I buy it?” I made the VWB myself by modifying a store-bought rake (with thin spring steel wires).
You can buy many different kinds of rakes, but the ones I use have spring steel wires angled down at the end — this part is about 12 cm long (AB in Figure 2), and the main part of the wire (BC in Figure 2) is about 35 cm long.
I recommend making your own VWB to help you understand how it works. You will also be able to improve it by using your own ideas (technological self-sufficiency).
The rakes use stiff spring steel wires that radiate out in a fan-like manner. Looking at the shape of the broom, many people think that vegetables will be uprooted in addition to weeds. Widen the space between the steel wires on one of the rakes and try hawking an appropriately sized vegetable.
It is possible to use one rake, but the weeding effectiveness improves significantly if three or more are used in series. As shown in Figure 2, I use four rakes held together. As you can see in Figure 2, the wires jut out toward the left when seen from the handle, and some of the wires are cut off with wire clippers to leave only six on each rake.
The handles on each rake, except for one, are cut off at a length of around 60 cm. The distance between the tips of the wires (tines) on each rake in the series is about 12 cm (m in Figure 2). Using cardboard as packing material, secure the four handles firmly in place using duct (waterproof) tape.
The distance between the wires on each of the rakes is adjusted to about 6 cm. The rakes usually come with a metal tool for adjusting this distance (B in Figure 3). This adjustment is very important. If it is not just right, the vibration does not work correctly.
The final stage is to try hawking a plot of soil that has no weeds or grass. Look at the shape of the track to ensure that the wires are moving correctly and adjust them while looking to see how they interact together. You can also adjust the angles of the wires on each of the rakes so that the wire tips are all on the same plane (i.e. they all touch the ground at the same time). This may sound complicated, but it’s easy to do.
Mechanism of Interplant Weeding
In the paddy fields where I rotate crops, the crops germinate about two weeks after sowing. At about the same time, the sprouts of a great variety of early weeds, including shortawn foxtail (Alopecurus aequalis), green foxtail (or bristlegrass, a species of annual grass, Setaria viridis), Japanese barnyard millet (Echinochloa esculenta (A. Braun) H. Scholz (1992)), chickweed (or stitchwort, Stellaria sp.), shepherd’s purse (or shepherd’s pouch, Capsella bursa-pastoris), lambsquarters (Chenopodium album), buttercup (Ranunculus japonicus) and others show above the surface of the soil to form a green carpet over the whole paddy field if left undisturbed.
Weed (3) in Figure 3 is one that has just sprouted from a shallow point beneath the surface of the soil and has not yet sent out roots. Weed (4) is one that has just sprouted by sending up a mesocotyl from some distance below the surface of the soil and has almost no roots.
Although there are exceptions, almost all early-stage weeds have thin roots that spread out just below the surface of the soil or have almost no roots at all. In contrast, crop plants such as rice, cereal grains, soybeans, vegetables and so on, compared with weeds, have strong roots which spread firmly and penetrate down to a deeper level (around 3 cm). This early-stage dissimilarity is vitally important in hawking.
Movement of the Wires: Vertical Vibration
As you pull the VWB along the ground, as in A in Figure 3, the tip of the VWB wire pierces the soil under the roots of the weed at an acute angle, like a hoe, catching onto the roots and pulling them upward and pulling the whole weed out of the ground. It then drops the weed on the surface of the soil, where it withers and dies.
By a combination of the wire’s own weight and the power used to pull the broom, the tip of the wire is always forced to pierce the soil at an acute angle, but as it pierces deeper it meets with the resistance of the soil and is pushed back but then returns to the original position due to the force of repulsion in the stiff spring steel wire. Thus the tip of the wire vibrates vertically, piercing the soil at almost the same depth (1 to 2 cm) as the broom moves forward.
What happens with weeds like Weeds (3) and (4) in Figure 3 that have not yet developed roots that the tip of the wire can catch onto immediately after sprouting? These will be weeded by the horizontal vibrating motion of the wires. Figure 2 shows the overall view of a VWB with four rakes in series. Grasping the handles R and S, if you pull the VWB over the crop plants, i.e. perform interplant weeding, each of the wires, spread out like a fan, pierce the ground at an acute angle, and due to the resistance of the soil and the springiness of the steel wire, oscillate (vibrate) horizontally violently and noisily, stirring up the soil as they go.
The result of this is that the Weeds (3) and (4) in Figure 3 that have not yet developed any significant roots will be moved around with the soil, and their roots (if any) and mesocotyl being severed will dry out, be buried, wither and die.
The wires are made to jut out to the left of the overall VWB in order to make good use of this special property of the fan-like arrangement of the wires. At first, I carried out hawking with the rakes arranged symmetrically with respect to the backbone of the VWB. When I did that, the central wires located just under the backbone hardly showed any horizontal vibrations at all and weeds remained for a certain interval on both sides of the wires.
Structure of the Multi-Rake Broom
Why does the VWB use four rakes? Naturally, the smaller the distance between the wires, the more effective we would expect the weeding to be, but things are not that simple. This is because the crop plant’s leaves and stems become sandwiched between the wires, which will also pull along rice straw and clumps of soil, or push over, rip out or bury the crop plants.
In contrast, if the distance between the wires is too large, some weeds will remain in the soil after you have carried out the hawking. The multi-rake broom structure resolves this problem. As in Figure 2, there are four rakes in series, and the distance between the wires is set at 6 cm.
Since the early-growth vegetables are small, they easily pass through the 6 cm interval, and they are not pulled out by the roots. However, since the wires of each of the rakes are aligned so that they are offset from each other (i.e. are not following on from one to the next in a straight line), from the viewpoint of the weeds, which have shallow roots, this is the same as having a gap between the wires of 6 cm divided by 4=1.5 cm. Moreover, the horizontal vibrations of the wires further decrease this 1.5 cm gap, pulling out and pushing aside the weeds, providing satisfactory weeding.
Vibrating Weeding Broom At-A-Glance
The soil is pierced at an acute angle: The rakes from which the VWB derive pierce the soil at an obtuse angle, as seen in Figure 4. With the acute angle, the resistance of the soil is greater, and the spring steel wires catch onto the weeds, lifting them up out of the ground as the wires vibrate strongly both horizontally and vertically due to the properties of the spring steel wire. In contrast, the spring steel wire weeding machines produced by British and Japanese makers, as in Figure 4, have the tips of the spring steel wires make an obtuse angle with the ground surface, seemingly stroking the soil. This is perhaps a different way of thinking about the weeding mechanism. View hawking video at bit.ly/2uaZyas.
The VWB is a specialized interplant weeder: The VWB focuses on the interplant space to carry out aggressive interplant weeding.
Requires less labor and strength and is speedy: To perform interplant weeding of 100 meters of vegetables with a triangular hoe or by hand will take you two hours. If the conditions are right, carrying out hawking over 100 meters will take one minute. Check out the video clips!
Pocketbook-friendly appropriate technology: A rake will set you back 980 yen ($11) in the Japanese DIY store. This is appropriate and simple technology that is cheap and can be handmade by farmers. This is the kind of simple technology that many people all over the world have worked to produce throughout the long history of humanity.
Practical Hawking for Weed Control
The mechanism of hawking differs from all conventional weeding techniques and requires some further thinking and tweaking. The technique is still in the trial-and-error testing stage, but the following are a few key observations I’ve made.
Plowing carried out before sowing or transplanting of the crop plants is done to break the soil up into fine particles so that the weeds do not survive. If quite large weeds are remaining at this stage, they cannot be dealt with by hawking. However, it is not necessary to break up all the soil in the ridges and furrows into fine particles. I break up the surface layer of the ridges to a depth of 1 to 2 cm.
Grains such as rice directly sown into dry fields, wheat and other cereal grains, soybeans, maize and so on have large seeds, robust and flexible leaves and stems and sturdy roots and are therefore the easiest crops for use with hawking. Interplant weeding by hawking is also very easily done on potatoes and the yam eddoe (Colocasia esculenta (L.) Schott) at the early stage.
However, these crops are generally cultivated using land-extensive methods. For larger areas, it will be necessary to mechanize hawking. Since around 2007, I have been collaborating with the development division of the Fukuoka agricultural machinery maker Orec to develop a weeding machine for dry fields. Since February 2016, after much creative activity, we have started work on the mechanization of hawking.
We found that, among sown vegetables, hawking works well with daikon radish, white turnip, Japanese mustard spinach (Brassica rapa var. perviridis), spinach, edible chrysanthemum (Chrysanthemum coronarium), potherb mustard (Brassica rapa var. nipposinica), burdock and others. However, if the leaves and stems are pulled too much, branched roots occurred in burdock, and the white turnip became an oval shape. It is especially important when trying out hawking to experiment and find what works best for your farm.
Among the transplanted vegetables, hawking was found to work well with cabbage, lettuce, takana (Brassica juncea var. integrifolia), katsuona, onion, kujo leek, chives and others.
In general, as transplanted vegetables have firm roots that go deep into the soil, once they get settled into the soil hawking is a very suitable technique for weeding. In contrast, it was surprisingly difficult to use hawking with Chinese cabbage and carrots. I intend to take up the challenge with these crops again this year.
There’s no simple answer to the question, “What’s the right time to carry out hawking?” I look at the condition of the crops and weeds and make a judgment based on what I see. In general, a good time is when the crop plants have reached a certain size and the weeds are just beginning to sprout. In reality, however, the weeds sometimes sprout and grow before the crop plants do. In this case, I carry out inter-row hawking before interplant hawking. When the soil on both sides of the crop row is soft and loose it is easier to carry out interplant hawking. Once the weeds exceed 3 to 5 cm in height, the roots are generally quite strong and it becomes difficult to remove them by hawking.
In contrast to conventional weeding methods, weeding is not completed by carrying out hawking just once. During hawking a number of times the vibration of the wires makes the soil soft and loose, fewer weeds are seen and it becomes more difficult for them to grow.
By carrying out hawking intensively two or three times when the crop plants have reached a certain size eliminates weeds well. If the interval between hawking sessions is too long, the weeds will become larger and much more difficult to remove by hawking.
As a rule, hawking should be carried out when the soil is dry. The soil will then become soft and loose and the weeding effect will be better. With some types of soils, however, when the soil is very dry it will be too hard for the tines to penetrate in some places. In these cases, it is probably effective to carry out hawking after rain has fallen and the surface of the soil is softer.
Troubleshooting to Avoid Crop Damage
• Issue: The crop plants are still small and the roots are not yet well developed. Solution: Wait.
• Issue: The wire tips pierce too deeply. Solution: Adjust the angle of the wires and the weight of the VWB.
• Issue: The wire tips do not pierce the soil and pass over the leaves of the crop plants. Solution: Adjust the angle of the wires and/or lower the handle when pulling the VWB.
• Issue: The crop plants are injured just by contact with the wires (this mainly occurs in the morning with lettuce when the leaves are a little stiff after absorbing a lot of water). Solution: In the afternoon, when the temperature has risen and the leaves are wilting a little from the sun and wind, hawking can be carried out by increasing the interval between the wires and passing slowly down the row. It is also possible to fix some sponge rubber on the wires to prevent leaf damage.
• Issue: Lumps of soil and straw get caught between the wires, causing the crop plants to get pushed over. Solution: Increase the interval between the wires and carry out more careful plowing.
• Issue: The crop plants become covered in soil. Solution: The crop plants are too small; wait a while. Increase the interval between the wires and pass down the row more slowly.
This article was originally published in Japanese in Tsuchi to Kenko (Soil and Health – journal of the Japan Organic Agriculture Association), July 2017 (#475). pp. 16-22
To contact Takao Furuno, email firstname.lastname@example.org. ne.jp (the author asks that readers please keep inquiries short and easy to understand for a non-native English speaker).