Variable-rate seeding is a practice you should adopt with today’s precision farming technology and hydraulically driven planters.

Considering high seed costs, erratic weather conditions and low commodity prices, you can’t afford to overseed and lose money or underseed and lose yield. Changing seeding rate on the go based on soil type and yield history is an important way to improve farm profitability.

When planting soybeans into better soil with higher yield potential, it’s best to lower the seed rate, while marginal soils or landscapes require higher seed rates.

Establish your base population. It seems safe to say that most producers are dropping 140,000 to 150,000 seeds per acre. That is probably a very safe population because you can lose 10 to 15 percent of the seed due to various issues like pathogens, rot and failure to germinate. And we always need to keep in mind that an even stand with 100,000 plants per acre at harvest will maximize yield.

Determine your variable populations. Here are three ways to determine optimal population:

1.  A hydraulic drive will allow you to easily change populations in individual strips across the field. Using a yield monitor you can determine which rate gave you not just the highest yield, but best return on seed investment.
2. Today’s planters are wide with two seed tanks and split with two different drives. Set your planter with your normal fixed-rate population on one side and a different fixed rate on the other side and then harvest each separately.
3. Overlay yield and soil maps to identify high- and low-producing areas and then plant across them at three rates: Normal, 20 percent less and 20 percent higher. Then use the yield map to tease out the optimal population for each zone with best return on investment.

Ascertain your population range. Changing population depends on identifying appropriate management zones. Identify management zones based on soil, water holding capacity and yield over multiple years. You only need about three zones per field and three rates.

The secret is to plant more seed in variable, drought-prone, timber and shallow soils. We need to close the canopy before the soil gets too dry and hot. So, population spread should be 10, 15 or 20 percent higher in low-yield areas. For example, use populations of 160,000 to 170,000 on poorer, lighter soils.

On well-drained, deep prairie soils with race horse production capacity and intense management, you can reduce the population to 125,000 to 130,000 seeds per acre. Maintain a base of 140,000 to 150,000 seeds per acre on average production areas.

Experience over the past decade has taught us that we can capture more yield in low yield zones by increasing population and save seed costs in high-yield zones by reducing population.

To learn more about variable rate seed and variable population listen to this webinar sponsored by Beck’s Hybrids.

Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.