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German farmers: ‘Not yet autonomous enough for us to manage weeds’

Christian Overkämping pulls a group of organic onions to show a quantity of 4 onions where he expects to find 8 on average. “It is highly unlikely that 4 out of 8 onions didn’t germinate or survive.”  - Photos: Jan Willem Schouten
Christian Overkämping pulls a group of organic onions to show a quantity of 4 onions where he expects to find 8 on average. “It is highly unlikely that 4 out of 8 onions didn’t germinate or survive.” - Photos: Jan Willem Schouten

Weeds can become a farmer’s nightmare. And for organic farmers, weeds can even become their worst nightmare. Three German farmers tried combatting weeds using automation and robotics. With varying degrees of success.

At a stone’s throw away from the Dutch border, farmers Georg Honsel and his wife Verena and Christian Overkämping operate two arable farms. Honsel Agrar is a conventional farm with 109 hectares and Einfach Bio is an organic farm with 35 hectares. Georg is in charge of the conventional side of the business while Verena and Christian run the organic farm. Both farms share an office and farm buildings in Rhede, close to the town of Borken.

Anyone who can manage weeds, can farm organic

The organic onions are usually pre-sprouted in 4 by 4 centimetres cups/pots to give them a head start. Every cup/pot contains 7 to 9 onion seeds and once emerged, the pre-sprouted onions are planted late March at a 15 centimetres intra-row and a 75 centimetres row distance on 3 metres wide beds. The head start is a great benefit but all in all, € 8,000 worth of onion plants is trusted to the ground!

Because of the head start they’re given, the onions can be hoed basically right away using the 8-row Schmotzer hoeing machine from the farmer Honsel Agrar cooperates with. “Hoeing not only affects existing weeds but it also keeps the soil surface moving preventing other weeds from germinating”, Christian says. Once the onion plants reach a certain size, hoeing is no longer possible. “Which is quite a challenge as I believe that anyone who can manage weed issues, can run an organic farm.”

The conventional side of the business was able to use an Ecorobotix Ara mounted behind an Amazone sprayer for spot spraying and had great success with it in carrots, green beans, onions and spinach.  - Photo: Matthias Honsel
The conventional side of the business was able to use an Ecorobotix Ara mounted behind an Amazone sprayer for spot spraying and had great success with it in carrots, green beans, onions and spinach. - Photo: Matthias Honsel

Great success with Ecorobotix Ara

On his conventional farm, Georg is using a trailed AP Dubex field sprayer for fungicide and herbicide applications but the use of herbicides also hinders the growth of onions, he says. “To deal with that and to save on herbicide usage, two conventional colleagues of mine invested in an Ecorobotix Ara.” This implement with 156 nozzles on 6 metres working width enables site specific herbicide application, spot spraying actually, on 6 by 6 centimetres spots.

“We were able to use the Ara on our conventional farm and had great success with it in carrots, green beans, onions and spinach. Because of our 3 metres wide beds, we mounted it behind an old Amazone self-propelled sprayer and that worked perfectly. At working speeds of about 8 km/h the capacity is sufficient. Waving onion stalks are a challenge for the cameras of the Ara system however and once weeds get too large, especially with Lambsquarters, the Ara can’t ‘beat’ them anymore. But other than that, the Ara eliminated up to 99 percent of the weeds!”

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Both farms share these farm buildings in Rhede, close to the town of Borken. -
Both farms share these farm buildings in Rhede, close to the town of Borken. -

Finding an organic solution

As the Ecorobotix Ara uses herbicides, the implement can’t be used in the organic crops of Einfach Bio. Like many other organic farmers, Verena Honsel and Christian Overkämping rely on own and external manual labour for weeding. “The availability of manual labour for weeding is becoming a huge challenge and we were on the lookout for alternatives”, Verena explains. While attending a demo in Bielefeld (Germany), Verena witnessed a FarmDroid FD20 field robot successfully sowing and hoeing onions. “That seemed to be a very good idea and we inquired ourselves at Solar-Energie Andresen, a solar energy specialist who’s also distributing and renting out FarmDroid FD20 robots.”

Christian: “We didn’t want to rush into conclusions so we tried and tested a FD20 during the winter of 2022 with the ambition to sow and hoe 6 hectares of organic onions and 1.5 hectares of conventional onions in 2023. We had some concerns about the navigation as the coverage of cell phone networks in Germany isn’t very good, but the robot followed the AB-lines perfectly.”

Raising the plant elements

Another aspect was the existing ground clearance of the seeding elements of 15 centimetres. “We wanted to raise this to 25 centimetres to prevent damage to the onions later in the season and so we did. We were told to be the first users raising the ground clearance like that. As prilled onion seeds are too expensive for us, we used untreated onion seeds that are typically irregularly shaped. To obtain the ideal 8 onion seeds per position and 100,000 seeds per hectare, we had special seeding discs made on a 3D printer. A constant number of seeds is very important because this affects the eventual size of the onions. Our trials during the winter were to our liking and the static calibration tests proved to be successful with a deviation of plus and minus 20 onion seeds per square metre.”

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This photo shows the irregular amount of onion seeds that ended up in one group. “We wanted 8 seeds on average to obtain uniform onions and minimal weed pressure but ended up having groups of 4 up to 12 onions.”  - Foto: René Koerhuis
This photo shows the irregular amount of onion seeds that ended up in one group. “We wanted 8 seeds on average to obtain uniform onions and minimal weed pressure but ended up having groups of 4 up to 12 onions.” - Foto: René Koerhuis

Sowing at the last minute

Although all preparations and precautions seemed to be in order, Spring was on the doorstep and until late April the weather had been unfavourable with low temperatures and a lot of rain. “It was quite uncommon for us, but we had to do two passes with the power harrow to obtain a good and even seedbed for sowing with the FarmDroid. An even seedbed is very important for maintaining an optimal seeding depth. In hindsight, we think the soil became too compacted, too consolidated for the onions seeds to germinate well enough.”

The sowing pattern deviated from what the calibration tests had shown

Finally, on 5 May 2023, Christian and the rented FarmDroid FD20 made it to the field to sow the onions. “5 May really is one of the last days you should sow onions in our region so we really were under time pressure. We of course checked the first results while sowing but because of the time pressure, we focussed on getting the seeds in the ground after all rather than on the correct number of seeds per position.”

Irregular sowing pattern

The 1.5 hectares of conventional and 6 hectares of organic onions were thus sown with the field robot. As soon as the onions started to emerge, Christian noticed that the sowing pattern deviated from what the calibration tests had shown. “We noticed different things. Although the intra-row sowing distance of 15 centimetres was perfectly maintained, each position contained between 4 and 12 seeds. Yes, on average that comes down to the desired number of 8 seeds per position, but 4 onions in one spot led to much larger onions than 12 onions in one spot. We think this might have had to do with the absence/lack of seed scrapers on the metering units of the seeding system.”

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The FarmDroid FD20 field robot that was used to sow and hoe 6 hectares of organic and 1.5 hectares of conventional onions in 2023 on a pallet, waiting to be picked up again by the owner. Honsel Agrar and Einfach Bio won’t use it again although they had high hopes of their first autonomous adventure.
The FarmDroid FD20 field robot that was used to sow and hoe 6 hectares of organic and 1.5 hectares of conventional onions in 2023 on a pallet, waiting to be picked up again by the owner. Honsel Agrar and Einfach Bio won’t use it again although they had high hopes of their first autonomous adventure.

Bad vibrations and a 5 Euro banknote

Vibrations and the inclination of the terrain also had their effects: fewer seeds uphill and more seeds downhill. “We also noticed that on the 6 different rows, the seeds were not aligned/synchronised perpendicular to the driving direction. While normally all seeds are to be aligned within a band width the size of a 2 Euro coin (2.5 cm, 1 inch), we saw a band width the size of a 5 Euro bank note. We think this was caused by the raised frame in combination with the rather short parallelogram linkage of the sowing units and coulters. These had to work under a more vertical angle to the ground and that affects the travel of the coulters. We believe this led to the seeds not being aligned well enough perpendicular to the driving direction.”

“This normally wouldn’t have been an issue if it weren’t for the FarmDroid FD20 mapping the position of each group of onions for hoeing purposes. While doing so, the field robot relies on that position being equal for each of the 6 rows. “And that was not the case, resulting in much worse than expected hoeing results and a lot, I mean a lot, of manual weeding. That was quite a disappointment to us”, Christian explains.

‘Just not autonomous enough yet for us’

Looking back, the farmers enjoyed working with the field robot and both Christian Overkämping and Georg Honsel were impressed by the simplicity of the sowing system. Christian: “We didn’t sow part of the headland for manoeuvring purposes but could have sowed it since the FD20 doesn’t need that much space to turn. But I have to admit that while sowing and hoeing, we needed to go to the field quite often because the robot stopped working. Maybe our expectations were (too) high, but for us, the FD20 is just not autonomous enough yet. We had to intervene too often. Luckily we rented the robot and didn’t buy it.”

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A close-up of the seeding unit of the field robot. The metering units lack a scraper and the farmers think this might have led to the uneven number of onion seeds per group.
A close-up of the seeding unit of the field robot. The metering units lack a scraper and the farmers think this might have led to the uneven number of onion seeds per group.

Particularly intrigued by laser weeding

Their experiences led to the conclusion that the FarmDroid FD20 is not a match for Honsel Agrar and Einfach Bio. Solar-Energie Andresen came to pick it up again not too long after Future Farming’s visit. Both farms are now on a quest for a better weeding solution for their farm. “At the moment we are particularly intrigued by laser weeding and have already contacted some companies working with laser. The challenge however is that many are not market (or farmer) ready yet, while others choose to concentrate on their home market. Such as some American startups/companies do”, Georg concludes.

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Koerhuis
René Koerhuis Precision Farming Specialist





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