Can variable-rate seeding increase harvest yield? Experimenting with hybrid corn

Hypothesis 1. High productivity zones can provide a larger quantity of plants with moisture and nutrients. Low productivity zones provide these resources to fewer plants.

To test the first hypothesis in high productivity areas, I increased the seeding rate. In low productivity areas, I decreased it. I can confirm the theory if I notice an increase in yield in the high productivity zones, but low productivity zones remain the same or all grow.

Hypothesis 2. Plants in high productivity zones compete for sunlight because they’re not deprived of nutrients or moisture. If we decrease the seeding rate here, the competition drops, and a smaller number of seeds results in larger crop yield. Low productivity areas show the opposite: plants are evenly depressed. If we increase the seeding rate, the yield might increase.

If the yield increases in both zones, with variable-rate seeding, then that hypothesis is confirmed.

Alpha Field’s area is 112 hectares. The relief has a difference in elevation of 56 meters.

Determining productivity zones. I identified productivity zones based on multiple years of vegetation data that I acquired from satellite images. From year to year, the vegetation data for different parts of the field hadn’t changed. That’s why the productivity zones in this field were pretty stable.

Finding the limiting factor. To determine the reason why the field was heterogenous, I studied the relief map, soil brightness data, and soil test results. The farm hired a third-party company to do the soil test.

I came to the conclusion that the primary factor affecting crop yield is the field’s terrain; in this case, the length and steepness of its slopes. A long, steep slope retains snow and water poorly. Consequently, during the growing season, these areas see insufficient moisture and, as a result, low yield values.

We can confirm this if we compare the relief map with the productivity zones map. High productivity zones are situated in flat areas of the field and in drainage hollows. These parts of the field retain much more moisture than the slopes during the growing season.

Evaluating the germination rate. One cornstalk can grow several ears of corn. That’s why the farm’s workers and I counted both the number of sprouts and ears of corn.

I marked two to three points in zones with variable-rate seeding. Farmworkers walked to the designated point, manually counting the number of sprouts and ears of corn in an approximately 10-sq. meter area.

I delineated 156 homogenous plots. I established the experiment’s results based on the average yield value in the homogenous plots.

High productivity zone. In all homogenous plots with seeding rates of 75,000 seeds per hectare, I noticed a pattern of 2−4 more quintals (1 quintal = 100 kg) in yield compared to plots with a seeding rate of 72,000 seeds per hectare. According to my calculations, the average growth when increasing the seeding rate by 3,000 seeds was 2.5 quintals.

I noted the opposite in areas with a seeding rate of 50,000 seeds per hectare, where the yield fell by 2−7 quintals.

Moderate productivity zone. I did not detect consistent yield growth when increasing the seeding rate from 60,000 to 72,000 seeds per hectare. In some areas, the yield decreased by 3 quintals, while in others, it grew by 2. Another factor most likely affected the yield.

Low productivity zone. I did not notice any pattern of yield change here with seeding rates of 50,000 and 75,000 seeds per hectare. In the area with a seeding rate of 72,000 seeds per hectare, the yield increased by 1.3 quintals. But this area was in the top part of the low productivity zone. This part of the field can be considered the border area between the low and moderate productivity zones. I did not factor these results into my conclusion. As it turns out, the yield in low productivity zones also failed to increase with a higher seeding rate.

Let’s call the second field Omega.

Omega Field’s area is 78 hectares. Its relief, soil brightness, and soil test results are similar to Alpha Field’s. Alpha and Omega Fields are next to each other. Both fields also had the same limiting factor, their relief. The only difference between the two fields was the hybrid that I planted. In every other regard, the reasoning behind the experiment for Omega Field was the same.

Omega Field’s most productive part was the drainage hollow and areas with slopes of up to 2 degrees. For the most part, low productivity zones are areas with a slope of over 3 degrees.

Creating a prescription map. Just as with the first field, I created the prescription map based on productivity zones.

In the second field, I used my previous approach to the seeding rate, i.e., I increased the seeding rate in high productivity zones and decreased it in low productivity zones. I laid down two test strips once again, this time, to test the alternative hypothesis. One with reverse logic for the seeding rate and one with the farm’s standard seeding rate (72,000 seeds per hectare).

Evaluating the germination rate. The hand count of sprouts and ears of corn in the second field yielded the same results. The seeding rate didn’t affect the corn’s germination rate.

Analyzing the crop yield. After harvesting Omega Field, I began to analyze the yield map based on homogenous plots.

In this experiment, I confirmed the first hypothesis regarding the increase in yield through variable-rate seeding. When variable-rate seeding was applied in Alpha Field, the corn yield increased. Both the hybrid selected for the experiment and the system for determining seeding rates affected the yield’s growth. I had the same result in several other cornfields with the same hybrid. This indicates that I also proved my hypothesis about hybrids' effect on the results of variable-rate seeding in the conditions experienced in 2019.