Variable-rate seeding. An experiment with soybeans_Cover_OneSoil Blog
Can variable-rate seeding increase yields?
Estimated reading time — 15 minutes
Experiment conducted — May-September 2019
Experimenting with soybeans.
Philip Kondratenko_OneSoil Agronomist
Usevalad Henin
Usevalad is an expert in GIS and agricultural chemistry. He has been developing precision farming tools since 2013. He is also the co-founder of OneSoil.
Last year, I tested variable-rate spring seeding in Ukraine and Russia to see how different crops react to this technique. I conducted the experiment in this article in conjunction with MHP agricultural holding in Ukraine. The company’s fields cover a total area of approximately 400,000 hectares. MHP grows corn, sunflowers, wheat, soybeans, and rapeseed. We’ve been conducting joint experiments for two years now. In 2019, we tested variable-rate seeding for soybeans.
The area of the field where the experiment took place is 33 hectares. Last year, perennial grasses were growing on the field. Just like for any grain crop, that’s a good precursor for soybeans. But 2019 was a dry year in Ukraine. Temperatures rose dramatically starting in June, and the country only received sporadic rainfall.

In this article, I’ll discuss how we conducted the experiment in these conditions and whether I managed to increase crop yield with variable-rate seeding.
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Last year, I tested variable-rate spring seeding in Ukraine and Russia to see how different crops react to this technique. I conducted the experiment in this article in conjunction with MHP agricultural holding in Ukraine. The company’s fields cover a total area of approximately 400,000 hectares. MHP grows corn, sunflowers, wheat, soybeans, and rapeseed. We’ve been conducting joint experiments for two years now. In 2019, we tested variable-rate seeding for soybeans.
Usevalad Henin
Usevalad is an expert in GIS and agricultural chemistry. He has been developing precision farming tools since 2013. He is also the co-founder of OneSoil.
The area of the field where the experiment took place is 33 hectares. Last year, perennial grasses were growing on the field. Just like for any grain crop, that’s a good precursor for soybeans. But 2019 was a dry year in Ukraine. Temperatures rose dramatically starting in June, and the country only received sporadic rainfall.

In this article, I’ll discuss how we conducted the experiment in these conditions and whether I managed to increase crop yield with variable-rate seeding.
The OneSoil team helped analyze and plan fieldwork throughout the experiment; MHP’s representatives decided which seeds and equipment to use.

Experiment hypotheses

Main hypothesis. I based myself on the unique crop development features: soybeans branch well and form a bush up to a meter tall. Presumably, the plants will branch more actively in high-productivity areas. This may cause the plants to interfere with each other’s development, meaning the seeding rate can be decreased in these areas. The opposite works for low-productivity areas: we’ll increase the seeding rate.

Alternative hypothesis. Let’s assume that soil productivity affects the number of seedlings, not stem branching. High-productivity areas will provide nutrients to more plants, while low-productivity areas will provide to fewer plants. To test this hypothesis, I increased the seeding rate in high-productivity areas and reduced it in low-productivity ones.

An increase in the field’s yield would confirm either hypothesis.
Experimental Setup
  1. Delimit productivity zones.
  2. Identify the limiting factor.
  3. Configure prescription maps for equipment.
  4. Analyze yield maps.

Experimental Setup
  1. Delimit productivity zones.
  2. Identify the limiting factor.
  3. Configure prescription maps for equipment.
  4. Analyze yield maps.

Determining productivity zones

I delimited productivity zones in the OneSoil web app. The app analyzes the field’s vegetation data for the previous four years and automatically generates a final productivity map based on how the field developed during this period.
Productivity zone map in a soybean field_OneSoil Blog
Productivity zone map in a soybean field

Finding the limiting factor

To find the limiting factor for crop yields, I studied the field’s relief, soil brightness, and vegetation data for the previous four years.
Soil brightness_OneSoil Blog
Soil brightness. The lighter the soil is, the lower the organic nutrient content is
The field's organic nutrient content varies quite a bit. Humus distribution reflects the field's productivity zones but has no connection to the relief. In cases like this, I always recommend testing the soil acidity. The higher acidity accelerates the mineralization of organic nutrients in the soil and limits productivity. It turned out that two factors — humus content and the pH level — were beginning to affect the field's yield.

Creating a prescription map

To test both hypotheses, I had to use three seeding rates in low-, moderate- and high-productivity areas. These are the rates I used: 240 kg/ha, 212 kg/ha, and 160 kg/ha. I left a strip with the farm’s standard seeding rate, 212 kg/ha, as a control strip.
Prescription map_OneSoil Blog
Prescription map. The control strip was the one with the 212 kg/ha seeding rate. The second strip was intended to test the alternative hypothesis.

Analyzing the crop yield

The soybeans were sown in May, and the field was harvested in September 2019 using a combine harvester with yield monitoring. I downloaded the yield file from the combine’s onboard computer and visualized the map in the OneSoil web app. This can be done in the "Field data" section.
Soybean yield map_OneSoil Blog
Soybean yield map
The first thing that stands out is the way the yield zones are distributed. It changed compared to the productivity zone map. For example, the moderate-productivity zone in the center of the field became a high-productivity area, and the high-productivity zone partially became a moderate-productivity area. The weather conditions in 2019 (it was a dry year) and the unique features of the crop itself could explain the changes.

The second thing that stands out is that there are no obvious yield increases despite the wide range of seeding rates (160−240 kg/ha). I identified homogeneous zones in the field to reliably assess the seeding rate’s impact on yield. These are areas of the field with the same seeding rate at each point and approximately the same yield. I’ve put the average values for homogeneous zones in areas with varying productivity in the table.
Average yield, t/ha

How soybean yield changed

In the low-productivity zone. Areas with an augmented seeding rate saw their yield increase. The average yield increase with an augmented seeding rate is 3 quintals (1 quintal = 100 kg).

In the moderate-productivity zone. I didn’t notice any tendency toward yield changes with increased or decreased seeding rates.

In the high-productivity zone. Yield increased when cutting the seeding rate. The average yield increase with a reduced sowing rate is 0.5−1 quintal.

Experiment results

The experiment was a success. I confirmed the first hypothesis. In high-productivity areas, yield increased when cutting the seeding rate. In low-productivity areas, yield rose when increasing the seeding rate.

What this means for the future

Even though I proved the seeding rate's impact on yield, I won't risk making any recommendations based on the results. I studied how soybeans react to variable-rate seeding in just one field. That's not enough for overarching conclusions. In addition, the experiment's outcome may have been affected by weather conditions. Remember that soybeans are sensitive to moisture. The field where I conducted the experiment was not irrigated.

This year, I'm continuing to study variable-rate seeding. In particular, I'm researching the differences within and between spring and winter crops and the factors that may affect their yield. I'll definitely share my findings with you once I have them.
There are three things you can do:
  1. Experiment with soybeans in your own fields and test different hypotheses on seeding rates.
  2. Wait for the results and recommendations from our next experiments.
  3. Take part in our experiments. We'll do everything for you for absolutely free! Here's how experiments are conducted and what you need for them.

There are three things you can do:
  1. Experiment with soybeans in your own fields and test different hypotheses on seeding rates.
  2. Wait for the results and recommendations from our next experiments.
  3. Take part in our experiments. We'll do everything for you for absolutely free! Here's how experiments are conducted and what you need for them.

Join OneSoil's experiments!
Have you ever conducted variable-rate seeding? Feel free to share your experience.
Usevalad Henin
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