New research from Michigan State University reveals that narrowing in-row seed spacing can significantly boost total potato yields—but not always economic returns—depending on grading, variety, and planting depth. Understanding the balance between yield and cost is critical for potato producers looking to maximize profitability.
Michigan, one of the top ten potato-producing states in the U.S., plays a key role in supplying chipping potatoes to national processors. While MSU’s decades-long breeding efforts continue to produce improved varieties, questions remain about how to optimize planting practices for economic gain. A 2024 study by MSU researchers at Montcalm Research Center set out to answer a crucial question: How do seed spacing and planting depth influence both yield and profitability in seed potato production?
The Study: Setup and Scope
Three varieties were tested:
- Bliss (new)
- Mackinaw (new)
- Lamoka (established)
Four in-row spacings (7, 9, 11, and 13 inches) and three planting depths (3, 5, and 7 inches) were trialed. Using randomized complete block design and standard industry practices, the researchers collected data across a full growing season, assessing emergence, yield by grade, tuber quality, and estimated gross income at a market value of $17 per cwt (hundredweight per acre).
Key Findings
Total Yield and Gross Revenue
- 7-inch spacing produced the highest total and US#1 yield, boosting gross income by 2–11% compared to wider spacings.
- When measured only by total yield, the 7-inch spacing remained economically profitable despite increased seed costs.
US#1 Grading Tells a Different Story
- When only US#1 yield was considered (a higher market grade), the closer 7-inch spacing was no longer most profitable. Instead, 9-inch spacing achieved a better gross margin, as it balanced seed costs and premium yield.
Variety Response to Planting Depth
- Bliss and Lamoka: Performed best at 7-inch planting depth, achieving gross revenues of $7,123 and $6,035, respectively.
- Mackinaw: Preferred a shallower 5-inch depth, delivering the highest gross income of $7,395 and US#1 yield gross revenue of $6,545.
These variety-specific responses show that planting depth recommendations should not be one-size-fits-all.
Economic Takeaways
- Seed cost is the only variable cost considered in this first-year analysis.
- Closer spacing increases seed costs, but also plant populations—potentially requiring higher inputs (water, nutrients, etc.) in future trials.
- Grower returns improve with 7-inch spacing when total yield is the goal.
- For US#1 market returns, 9-inch spacing offers the best gross margin.
- This trade-off underscores the need to align production goals (volume vs. grade) with specific planting strategies.
Limitations and Next Steps
Researchers emphasize that these are preliminary results from a single growing season. Additional years of data will help confirm trends and account for:
- Environmental variability
- Additional input costs (fertilizers, water, crop protection)
- Other quality traits like tuber uniformity, specific gravity, and disease resistance
Future trials will aim to refine planting recommendations tailored to specific varieties and production objectives—from seed multiplication to chip processing.
This MSU study is a critical step toward data-driven planting recommendations in potato production. While closer seed spacing can boost total yields, the real economic advantage depends on variety behavior, planting depth, and target market grade. With seed costs and input use on the rise, fine-tuning spacing and depth could unlock both higher productivity and better profit margins—but multi-year research is essential to confirm these findings across conditions.
