Variable-Rate Seeding Without Using Special Equipment

The field covered an area of 68 hectares. The soil was chernozem with varying levels of degradation.

I identified the field's productivity zones using the OneSoil web app. They were pretty stable. That means that high- and low-productivity plots stayed in the same places from year to year.

After that, I analyzed the field's relief and soil brightness. In my experience, these two factors more often than not impact fertility and, as a result, crop yield in the field. This field was no different.

Relief. The field had an elevation difference of over 30 meters. And although there weren't any drainage hollows, low-lying areas, or higher grounds, the slope in some areas exceeded 4 degrees.

It’s hard to come to a straightforward conclusion on how the relief affects productivity using a relief map. But if you compare the slope map with the productivity zones map, you’ll see that they align almost perfectly. Productivity is low in areas that have a high slope and is high where the field is even. It turns out that one of the reasons for a field’s heterogeneity is precisely because of the relief.

Soil brightness. This depends on organic nutrient content. The darker the soil is, the richer it is in nutrients. Here’s an image of tilled soil with its top layer air-dried.

The map shows that the soil is lighter in areas where the slope is around 3 degrees. These same areas overlap with the low-productivity zone. That means that both the relief and the soil nutrient content affect productivity.

After that, I had to select a plot in the field where I would conduct variable-rate seeding. Since the seeding rate on the seeder could only be adjusted manually, I had to choose the most homogenous plot.

After analyzing information about the field, I outlined the zone that showed high productivity year after year. The soil in this zone is rich in organic nutrients, while the slope and the relief’s other morphometric properties (slope curvature, aspect, length, and direction) are the same. To determine more precisely the seeding rate’s impact on yield, I added a small nearby moderate-productivity plot to the zone.

I didn’t analyze the low-productivity zone in the experiment. It’s mostly on the field’s left side, far from the zone I selected for seeding. It’s impossible to sow at a precise rate there without special equipment.

To create a prescription map for the onboard computer, I set two seeding rates: 65,000 seeds/ha and 85,000 seeds/ha. I sowed the right part of the selected zone at the higher rate and the rest of the field at the smaller rate. Here’s what the prescription map looked like with a breakdown by rate.

Analyzing the crop yield. In the zone that I selected for variable-rate seeding, the harvest was done using a combine equipped with a yield monitoring system. That made it very easy for me to transfer all the data on the harvested crop to a computer.

You can tell by looking at the map just how much seeding rate affected field productivity. To understand by how many quintals the yield grew in moderate- and high-productivity zones, I divided the section of the field I experimented with into homogenous zones. That means that these zones had the same yield and seeding rate across their whole area. The combine passed through each zone two to four times.

The experiment worked! Even with only a manually adjustable rate, I was able to increase corn yield in the experiment zone. That means that the farm where I conducted the experiment can confidently plan to buy variable-rate seeding equipment and know that they’ll get a return on their investment.

Last year, I conducted variable-rate seeding experiments in 23 cornfields located in different zones and different conditions. In every single one, the experiment yielded positive results. I make the following recommendation to everyone who applies variable-rate seeding: