Proper plant spacing for soybeans is essential to maximize yields, optimize plant health, and improve management efficiency. Soybean spacing affects canopy development, light interception, disease management, and ultimately economic returns. Recent research combined with decades of field experience show that spacing decisions must consider row width, seeding rates, variety, environmental conditions, and management practices.
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1. Introduction: The Importance of Soybean Spacing
Soybean plants compete for sunlight, nutrients, and water. Adequate spacing ensures uniform development and canopy closure, which facilitates weed suppression and prevents diseases by improving airflow.
- Narrow rows (7.5 – 15 inches) generally increase yields by enabling quicker canopy closure.
- Wide rows (30 inches or more) are sometimes preferred for certain management practices, but can reduce yields.
- Seed population targets of 100,000+ plants/acre (adjusted for expected emergence) are recommended for most environments.
2. Row Spacing Recommendations
Research summarized by Purdue Extension and other sources recommends row spacing of 7.5 to 15 inches for maximum soybean yield. Narrower rows encourage more uniform seed placement and emergence.
| Row Width (inches) | Typical Yield Advantage | Notes |
|---|---|---|
| 7.5 – 15 | Baseline / Highest yields | Favored for rapid canopy development |
| 20 – 22 | Slightly lower by ~3-5% | Some prefer for equipment compatibility |
| 30 | ~7% lower yield on average | Increased disease risk in some cases |
(Source: Purdue Extension AY-217-W, and multiple university studies)
3. Plant Populations and Seed Spacing
Maximum yields require no less than 100,000 healthy plants per acre in 7.5- and 15-inch rows. In wider rows, higher populations may be necessary to maximize yield due to reduced plant interactions.
| Row Width (inches) | Recommended Plant Population (plants/acre) | Notes |
|---|---|---|
| 7.5 – 15 | 100,000 – 140,000 | Uniform emergence critical |
| 20 – 22 | 130,000 – 160,000 | To compensate for wider rows |
| 30 | 150,000 – 180,000 | Requires increased seeding rates |
(Adjusted for seedling emergence; see Table 2 for seeding rates)
4. Table 1: Soybean Seeding Rate Recommendations by Row Width and Plant Population
| Row Width (in) | Seeds per Acre (for ~130,000 plants/acre) | Seeds per Row Foot (for a 30-in. row) | Seed Spacing in Row (inches) |
|---|---|---|---|
| 7.5 | 130,000 | 26 | 0.46 |
| 15 | 130,000 | 13 | 0.92 |
| 20 | 150,000 | 10.4 | 1.15 |
| 30 | 160,000 | 6.5 | 1.83 |
5. Seed Depth and Placement
Soybean seeds should generally be planted 0.75 to 1.5 inches deep, with shallower planting in moist, heavy soils and deeper in light, dry soils for moisture access.
Uniform seed placement promotes uniform seedling emergence and plant development, which correlates with maximum yield potential.
6. Table 2: Row Width vs. Time to Canopy Closure and Yield
| Row Width (inches) | Days to Full Canopy (May Planting) | Yield Differences | Notes |
|---|---|---|---|
| 7 | 25 | Baseline (high) | Fast initial canopy |
| 15 | 40 | Slightly less | Good balance |
| 20 | 50 | Moderate decrease | Reduced light capture |
| 30 | 65 | 7-10% less | Slower canopy closure |
7. Yield Responses to Plant Population by Row Width
Yield advantage of narrow rows is most apparent with later planting dates, within shorter growing seasons, and high temperatures.
| Row Width (in) | Optimal Plant Population (plants/acre) | Expected Yield (bushels/acre) | Notes |
|---|---|---|---|
| 7.5 - 15 | 120,000 – 140,000 | 60 – 70 | Common recommended population |
| 30 | 150,000 – 170,000 | 55 – 65 | Higher population compensates |
8. Table 3: Soybean Plant Populations and Seeding Rates per Acre by Row Width
| Row Width (inches) | Desired Plant Population (per acre) | Seeds per Acre (accounting 90% emergence) | Seeds Per Foot of Row (30 in rows) |
|---|---|---|---|
| 7.5 | 130,000 | 144,400 | 28 |
| 15 | 130,000 | 144,400 | 14 |
| 20 | 150,000 | 166,700 | 12 |
| 30 | 160,000 | 177,800 | 8 |
9. Wide Rows vs. Narrow Rows: Pros and Cons
| Row Width | Pros | Cons |
|---|---|---|
| Narrow (7-15 in) | Faster canopy closure, better weed suppression, higher yields | Requires specialized planting equipment, closer plant care |
| Wide (20-30 in) | Better airflow, easier mechanical cultivation, less white mold risk in some climates | Slower canopy closure, reduced yields |
10. Table 4: Soybean Plant Populations and Yield Summary from Purdue Extension
| Row Width (inches) | Plant Population (plants/acre) | Approximate Yield (bushels/acre) |
|---|---|---|
| 7.5 | 130,000 | 65 |
| 15 | 130,000 | 65 |
| 30 | 160,000 | 60 |
11. Special Considerations for Soybean Varieties and Plant Type
- Bush-type soybeans: Can yield equally well as erect types in narrow rows with adequate populations.
- Plant uniformity and seed treatment improve stand establishment, enabling recommended plant populations.
- Row spacing decisions also consider equipment and field conditions.
12. Table 5: Recommended Soybean Spacing Adjustments by Soil and Environment
| Soil Type | Recommended Row Width (inches) | Notes |
|---|---|---|
| Heavy clay soil | 15–20 | Improves emergence due to soil crusting |
| Sandy or loam soils | 7.5–15 | Narrow rows for quick canopy closure |
| High disease pressure sites | 20–30 | Wider spacing reduces humidity |
| Short season areas | 7.5–15 | Rapid canopy helps maximize growing period |
13. Practical Tips for Planting Soybeans
- Use precise planters to ensure uniform seed spacing and depth.
- Adjust seeding rates based on expected emergence and soil type.
- Monitor plant population after emergence and replant if thinning is necessary.
- Consider weed control methods suitable for the chosen row width.
- Monitor for diseases, especially in narrow rows where humidity is higher.
14. Conclusion
Optimizing soybean plant spacing requires balancing row width, seeding rate, and environmental factors. Purdue Extension and extensive research recommend row spacing between 7.5 and 15 inches for maximum yields, with plant populations above 100,000 plants per acre. Wider rows may be suitable under specific conditions but generally yield slightly less.
By following recommended seeding density tables and adjusting for field conditions, growers can maximize soybean yields and profitability. Always factor in equipment, soil, and climate considerations when deciding spacing and population.
If you would like, I can provide customized plant spacing calculators, detailed seeding rate charts for your farm size, or tailored recommendations for your specific region and soybean variety.