Drone seeding: much to consider

The seeding drone has made its entrance into agriculture, including in the Netherlands. However, a fully developed system is not yet in place. Arable farmers in the Dutch Veenkoloniën region experienced in an experiment that taking a broad perspective provides useful insights for integrating drone seeding into their operations.

It is not easy to draw firm conclusions from a “farmer’s experiment.” This became clear on November 20, when experiences with drone-based underseeding of cover crops were evaluated. On 2 arable farms in Stadskanaal and Onstwedde, supported by the Dutch farmer experiments subsidy scheme, the effectiveness of drone underseeding was tested as part of the cultivation process. The experiment was supported by Aerovision and ABdrone.

Underseeding

Underseeding involves sowing a subsequent crop in a already present crop. The most well-known application is as a catch crop in maize. In this experiment, the cover crop was spread about 2 weeks before the barley harvest. Underseeding barley can count as an eco-activity, thus generating income. On a few plots, it might just be the boost needed to achieve bronze, silver, or gold status under the eco-scheme. This equates to €60, €100, or €200 per hectare across the entire area, depending on the farm.

Exploratory Research

“This is exploratory research,” says Leks Bolderdijk from ABdrone. As a result, no hard scientific conclusions can be drawn. “The advantage is that by looking broadly, we discover many different factors to consider.”

The study looked at the best sowing time and the impact of clay-coated seed on growth—more specifically, seed establishment. Positive effects on soil quality and biodiversity were also anticipated because the soil under the grain crop remained undisturbed from sowing until the next growing season. Underseeding with a fertiliser spreader is also possible, but only if the working width matches that of the sprayer. When the tramlines are too far apart, combining a fertiliser spreader with a drone becomes impractical. In such cases, using the drone alone is preferable. Additionally, drones allow for the optimal sowing moment, regardless of the field’s accessibility.

Favourable climate for drone seeding

As mentioned, firm conclusions cannot be drawn from the field experiments on the 2 farms. However, the evaluation provided various useful insights and suggestions for broader adoption of cover crops (or catch crops) in farming practices. Both the political and actual climate are favourable for drone seeding. Politicians are interested in cultivation techniques that promote biodiversity, partly by reducing soil compaction. Changing weather patterns are also increasing farmers’ need for reliable, weather-independent sowing techniques.

Find out which seeds perform better when sown on the surface. In that sense, we are currently sowing the ‘wrong’ cover crop seed

Using the wrong seed

The evaluation revealed various insights. Coating seeds (primarily with clay) improves seed establishment. The coated seed can remain dormant until the optimal moment (moisture) for germination. “A coated seed behaves as if it has been incorporated into the soil,” says Arjan Jansma from drone and coating company Qlobel. He also calls on seed companies to reconsider their approach to seed selection. “Look for seeds that stand out when they are not incorporated into the soil. Find out which seeds perform better when sown on the surface. In that sense, we are currently sowing the ‘wrong’ cover crop seed.”

Coating

Coating increases seed costs by about 10%. Jansma suggests that the required seed quantity could perhaps also be reduced by 10% with clay-coated seed. However, sowing coated seed becomes more expensive due to the additional drone flights required to distribute the planned amount of seed. There was no significant difference in drone seeding results between sandy and clay soils.

Further research

Further research is necessary—more scientific and long-term—with seed companies also involved. “As a farmer, I want more certainty about when, under what conditions, and how exactly I should sow,” says Gert Sterenborg. One of the trials took place on his farm in Onstwedde in the northern province of Groningen. The result of underseeding with uncoated seed on 6 hectares of barley with oilseed radish (sown in late June) disappointed him. A photo taken in early September shows a very irregular stand in the barley stubble. Where the oilseed radish is underperforming, there are significantly more weeds like chickweed, goosefoot, and grasses. The cause is unclear. Moisture? pH? Does it indicate soil quality issues? “Where we sowed conventionally under normal conditions, the stand is much more uniform.”

Which conclusions

For Sterenborg, the irregular stand is a reason to inspect the field more closely. The first observation is that there are many earthworms in the top layer and relatively many mushrooms in autumn. However, Sterenborg has no idea what conclusions to draw regarding the cover crop. Are mushrooms in your field good or bad? “We still know very little about fungi in the soil,” adds another participant. On Sterenborg’s other plot, where the cover crop performed better, no worms were found.

“We were too cautious with underseeding in this experiment due to concerns about competition with the main crop. In hindsight, we could have safely underseeded 2 months earlier,” says Bolderdijk of ABdrone. “Contrary to conventional wisdom, early sowing does not harm main crop yields due to competition for water and nutrients. The real issue is that the underseeded cover crop suffers from insufficient light and fails to develop properly under the main crop.”

Underseeding can even begin as early as January, especially if field accessibility is no longer a concern. It is also better to sow in maize at a height of 1 meter than at 2 to 3 meters, where it is too dark at the bottom.

Underseeding resulted in less foliage, more worms, and we expect the field will be more accessible in spring

Post-harvest seeding versus underseeding

There is also a need for more understanding of the differences between post-harvest seeding of cover crops and underseeding in standing grain crops. This includes evaluating whether a fertilizer spreader or drone is the best method. Such trials should also be paired with soil sampling to assess soil conditions and yield measurements. Bolderdijk adds, “With post-harvest seeding, the cover crop was clearly more robust, and grain stubble composted quickly. On the other hand, underseeding resulted in less foliage, more worms, and we expect the field will be more accessible in spring.”

At €75 per hectare, drone seeding is more expensive than the €10 per hectare cost of underseeding with a fertiliser spreader. Post-harvest seeding costs €200 per hectare, making it significantly more expensive than drone seeding. Jansma from Qlobel points out, “Tractors are becoming increasingly expensive, while drone seeding is getting cheaper.”

What is next?

All in all, the evaluation provided a wealth of information. Practical experiences, combined with farmers’ and drone pilots’ observations, were supplemented by concrete, well-established insights about drone underseeding. Everything is interconnected, which makes drawing firm, unambiguous conclusions after one year of experimentation impossible.

Farmers expressed a desire to continue experimenting on their farms. The question remains whether these trials can again be incorporated into subsidy schemes. Jaap Dun, an arable farmer from Musselkanaal and host of the evaluation, advocates for a more scientific approach. “We tend to draw conclusions only when things are blatantly obvious. In proper research, findings are often observed before we notice them in the field. With our current perspective, we miss these details.” Bolderdijk concludes, “It is a matter of money. Scientific research costs ten times as much as what we’re doing. Add another zero to the budget.”