Soybeans: Variable Seeding Rates – Maximizing Performance

©Debra L Ferguson Stock Photography

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:

  1. identifying uniform management zones, and
  2. 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/acre is usually adequate to maximize yield.
  • Use a higher seeding rate in poor areas of the field (for example, areas subject to seedling disease, crusting, or ponding).
  • In our first year of research, optimum seeding rates among management zones ranged from 100,000 seeds/acre to 180,000 seeds/acre.
  • On-farm trials with high, medium, and low seeding rate strips (~160,000, ~140,000, and ~100,000 seeds/acre) across the field will help farmers fine-tune the optimum seeding rate for their specific fields.
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)

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: William Hamman, University of Nebraska-Lincoln. Click Image to Enlarge


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