Unlocking the Power of Planting Date and Starter Fertilizer
Getting the basics right is often the key to unlocking higher yields.
For soybean growers, two fundamental decisions stand out at the start of every season: when to plant and whether to use starter fertilizer. While these might seem like simple agronomic choices, modern research reveals they are powerful levers that can significantly influence your final yield.
The timing of soybean planting sets the stage for the entire growing season. The old practice of planting soybeans only after corn is fully in the ground has been radically rethought over the past decade, as research consistently demonstrates the yield advantage of earlier planting 8 .
Research from Michigan estimates a 7% yield reduction when planting occurs on May 31 compared to May 1, with the majority of that decline happening after mid-May 6 .
Planting Period | Yield Potential | Key Characteristics | Primary Risks |
---|---|---|---|
Mid-April to Mid-May | Highest | Maximizes light interception, longer seed fill period | Late spring frost, cool soil diseases |
Late May to Early June | Declining | 0.35-0.51 bu/acre/day reduction after May 10 8 | Compression of reproductive period, early fall frost |
Mid-June & Later | Lowest | Requires higher seeding rates 6 | Early frost, incomplete maturity |
Data shows yield reductions of 0.35 to 0.51 bushels per acre per day when planting is delayed beyond May 10 8 .
Contrary to what one might assume, the very earliest planted soybeans aren't always the tallest. Research from North Carolina has revealed an unexpected quadratic relationship between planting date and plant height 3 .
The tallest soybeans consistently emerged from mid-April to mid-May plantings, while soybeans planted in mid-March to early April were often shorter 3 .
Research has established a positive correlation between plant height and yield up to about 36 inches, after which the relationship flattens 3 .
The question of whether soybeans benefit from starter fertilizer—particularly nitrogen—has been debated for decades. Soybeans have high nitrogen requirements, needing approximately 4.5 pounds of N per bushel of yield, with about 3.5 pounds of that removed with the grain 2 .
An 80-bushel crop therefore needs to accumulate about 360 pounds of N per acre 2 .
Historically, soybeans meet these substantial needs through a combination of:
By symbiotic bacteria in root nodules (50-60% of total N) 2
Of nitrogen from soil organic matter (the remainder) 2
A comprehensive multi-year study conducted across Illinois from 2014-2017 provides crucial insights into soybean response to fertilizer nitrogen 2 .
Location & Soil Type | Yield Response Pattern | Most Effective Application Timing | Key Takeaway |
---|---|---|---|
Chillicothe: Coarse-textured, Irrigated, Lower OM | Strong positive response (35-38% increase) 2 | Planting | Responsive environment due to lower natural N supply |
Brownstown: Claypan Soil | No significant increase 2 | Not applicable | Even with yield near 61 bu/acre, no benefit to added N |
Urbana/Monmouth: Deep Prairie Soils, Higher OM | Small, inconsistent response 2 | Multiple applications (modest benefit) | High natural N supply limits response to fertilizer |
To understand the real-world interaction between planting date and starter fertilizer, we can examine the methodology and results from the multi-year Illinois study that provided the data above 2 .
The research team established nine field trials between 2014-2017 across key soybean-growing regions in Illinois 2 .
Locations included university research farms near Urbana, Monmouth, and Brownstown, plus a farmer's field near Chillicothe with pivot irrigation 2 . This provided a range of soil types from coarse-textured soils with <2% organic matter to productive fine-textured soils with >3.5% organic matter 2 .
Six nitrogen fertilizer treatments were evaluated:
Soybeans were planted in May with regionally adapted varieties and managed using standard agronomic practices. All plots followed corn, with appropriate weed and disease control. Fungicide seed treatment was used where needed 2 .
Despite challenging conditions, the untreated control averaged 61.1 bu/acre. Applications of 100 lb N/acre at any single timing did not produce statistically higher yields compared to the control 2 .
Applying N at planting increased yields by 22.4 bu/acre in 2015 and 19.7 bu/acre in 2016 compared to the control 2 . The four-application treatment provided no additional yield benefit.
Yield responses were minimal. Only one of five site-years showed a significant response, which was actually a yield decrease of 5.2 bu/acre from planting-time N 2 .
Factor | Consideration | Practical Implication |
---|---|---|
Soil Type | Responsive on coarse-textured, low-OM soils; less responsive on high-OM soils 2 | Reserve N applications for specific soil conditions |
Yield Level | Negative correlation between yield potential and N response 2 | Highest-yielding fields least likely to benefit |
Application Cost | Multiple applications rarely economical 2 | Focus on single well-timed applications if used |
Commodity Price | Lower soybean prices reduce economic viability 2 | Strict ROI calculation essential |
Translating this research into practical management requires understanding both the opportunities and limitations:
The evidence strongly supports moving toward earlier planting when field conditions allow. The yield benefit is well-established, though risks can be mitigated using several key practices:
Based on current research, a more nuanced approach is warranted:
When nutrient deficiencies are visually confirmed, corrective applications may be warranted, but deficiency symptoms don't always translate to yield loss 5 .
The research on planting date and starter fertilizer reveals a compelling story: sometimes the most powerful management practices are the fundamental ones.
While inputs like foliar fertilizers and in-season nitrogen applications can seem technologically advanced, the evidence suggests they rarely provide consistent economic returns.
The real yield gains come from optimizing the basic agronomic factors—planting soybeans early in good soil conditions, selecting adapted varieties, and ensuring soil fertility fundamentals are addressed. As research continues to refine our understanding of these interactions, the principle remains clear: success in soybean production comes not from silver bullets, but from consistently executing the fundamentals based on sound scientific evidence.
For growers looking to maximize yields in the coming season, the message is clear: focus first on getting your planting timing right, assess your specific soil conditions, and let science—rather than tradition or anecdote—guide your fertilizer decisions.