Figure 1. Soybean plant architecture responds to planting population. At lower seeding rates, soybean plants tend to be shorter, have thicker stems, and more branches (left). At higher seeding rates, soybean plants tend to be taller, have thinner stems, and fewer branches (right). (Photo by William Hamman)

The majority of new planters are capable of variable rate seeding (VRS), or planting different amounts of seed in predetermined zones within a field based on a “prescription.” For VRS to be successful, zones within a field need to be relatively uniform, and the optimum seeding rate within each zone needs to be identified.

In 2017 and 2018, we conducted on-farm research with the objectives of:

identifying uniform management zones, and identifying the optimum seeding rate within each zone.

Identifying Uniform Management Zones

Creating management zones on a soil map unit is inaccurate. Creating management zones based on soil properties using high-density grid soil sampling or terrain attributes (e.g., elevation) is more accurate

If you use soil properties to create zones, make sure soil sampling techniques are consistent across the field (for example, collect soil from a consistent depth).

In our first year of research, elevation, potassium, and pH were important variables to consider when making management zones. However, variables to make a uniform management zone are field specific.

Identifying Optimum Seeding Rate Within Each Zone

When planting soybean in May, a final plant population of 100,000-120,000 plants per acre is usually adequate to maximize yield.