Yield potential declines rapidly if soybean planting occurs after May 24 (0.5% per day).
Final stands greater than 100,000 plants/A most often maximize yield potential.
Switching to a 0.5 earlier relative maturity (RM) variety shortened the time to maturation by 4-6 days.
Switching to 0.5 earlier RM produced less yield and revenue at all planting dates.
Introduction
Early soybean planting can help maximize photoperiod and avoid heat and moisture stress during critical flowering stages. Early planting can also help optimize soybean growth between vegetative and reproductive stages, helping improve yield potential. Balancing the time spent accumulating nodes during vegetative growth and the length of time in reproductive stages to fill pods is crucial to ensuring high yield potential.1 Early planting can also allow farmers to plant fuller-season varieties to help maximize yield potential and economic returns.2,3 However, there can be of poor stand establishment if germination and emergence are slowed due to cool, wet soils. Insects and disease can also be a bigger concern with early planting dates and should be managed accordingly. Golden Harvest® Agronomy in Action research trials were conducted in 2021 to demonstrate how planting date, RM and seeding rate interact with each other.
Graph 1: Multi-year planting date influence on soybean yield
Multi-year Planting Date and Seeding Rate Results
Results from historic Agronomy in Action planting date research conducted across NE, IA and IL has shown that yield potential is generally maximized if soybeans are planted before late May (Graph 1). If planting is delayed past May, yield loss potential can average 0.5% per additional day delayed.
Graph 2. Influence of final stand on yield using 23 site-years of data
Soybeans have been less responsive to increasing seeding rates as other crops, such as corn. Due to the lack of responsiveness, most farmers are more interested in understanding the minimum number of soybeans to plant to achieve a final stand that maximizes yields. Final plant stands are usually lower than actual seeding rates, and in many cases they can be significantly less. Multi-year seeding rate trials have shown that final stands greater than 100,000 plants/A typically maximized yields. Final stands greater than 100,000 plants/A sometimes resulted in small yield gains (Graph 2). There was a 2% loss in yield potential for every 10,000 fewer plants established when final stands were less than 100,000 plants/A.
Graph 3: Yield response by planting date
Planting date studies were conducted at Agronomy in Action sites in Seward, NE, in 2020 as well as Slater, IA, and Clinton, IL, in 2021. 3 soybean variety RM groups were selected to be planted at each location based on the average locally adapted RM, as well as 0.5 RM earlier and later. Within each of the 3 RM groups, 2 varieties were selected. All 6 varieties were planted at 100,000, 140,000 and 180,000 seeds/A. Maturity groups were stripped in each replicate to facilitate harvesting at appropriate timing based on maturity. Planting date responses behaved similarly across the 3 locations and followed general trends observed in multi-year planting date trials (Graph 3). Yields decreased with delayed planting in all locations and years, but at different rates.
Graph 4: Gross revenue by planting date and relative maturity
Maximizing RM to Optimize Returns
Farmers commonly select soybean varieties of differing RM for a several reasons. Early RM soybeans are often chosen to begin harvesting prior to corn reaching maturity. In other situations, early RM varieties are used when planting is delayed to reduce the risk of fall frost injury. However, shortening RM too much can reduce yield potential. Clinton, IL, Seward, NE, and Slater, IA, planting date yields were used to model gross revenue of each RM across all planting dates. Gross revenue was calculated based on $11.92/bu soybeans, which was the price at time of the study. Yield advantages observed with 0.5 RM later soybeans translated into higher revenues with April and early May planting dates (Graph 4). At all planting dates, mid and full RM varieties provided economic advantages over planting 0.5 RM earlier varieties (Graph 4).
How Soybeans Adapt to Planting Date
The number of days needed to reach maturity decreased with shorter season soybeans, although not as much as previously anticipated. Planting early RM varieties to enable earlier harvest only provided 4-6 extra harvest days when compared to the average locally adapted RM (Graph 5). The fullest season soybeans matured nearly 2 weeks after the earliest RM varieties. To reach maturity in fewer days with later planting dates, the soybean plant must adjust the amount of time spent in vegetative and reproductive stages. Later-planted soybeans accelerate through flowering stages (R1-R4) in fewer days and start filling pods sooner (Graph 5). A shortened vegetative period from delayed planting can also reduce the overall number of nodes per plant which is an important component of yield determination. Yield advantages of full-season RM varieties in these trials is likely partially due to an average of 6-8 additional days of vegetative growth in April and May planting dates when compared to earlier RM varieties (Graph 5).
Graph 5: Days to growth stage by RM and planting date. Number outside right of bars is mean total days to maturity. Summary
This study shows the importance of planting date and seeding rate on soybean management and the implications of economics on those decisions. Data from this season and previous years reinforce the need to begin soybean planting in the latter half of April and finish by mid-May to avoid yield penalties in most Midwest geographies. Conditions for plant establishment within the first 1-2 weeks of planting are critical, otherwise emergence dates may not differ from later planting dates. Yield benefits from early planting are dependent upon date of emergence rather than actual planting date. Both April and mid-May planting dates can maximize crop canopy closure early in the season which helps improve photosynthesis efficiency.
In years where planting is delayed, balancing between maximizing yield with a full-season RM and reaching maturity prior to frost with an earlier RM is important. These trials reinforced that when this happens, only small adjustments of earlier maturity soybeans are necessary to reach maturity faster and still maximize yield and revenue potential. In these trials, there was only a 7-day spread in maturation between the earliest and fullest season RM varieties when planted in June (Graph 5).
Seeding rates from 2021 and prior years suggest that planting 140,000 seeds/A will typically result in final stands greater than 100,000 plants/A and maximize yield potential. There are years that increasing seeding rates higher than 140,000 seeds/A have given slight yield benefits, but most often they don’t provide an economic return due to additional seed and seed treatment cost. If reducing seeding rates less than 140,000 seeds/A, it will be increasingly difficult to achieve the minimum final stand of 100,000 plants/A. Although yield penalties may not always be seen with reduced seeding rates, it will be more likely to occur as germination and stand establishment rates decrease.
To learn more about this study and how you can apply learnings to your operation, watch this video.
References:
1 Specht, J., J. Rees, G. Zoubek, K. Glewen, B. VanDeWalle, J. Schneider, D. Varner and A. Vyhnalek. 2012. Soybean Planting Date – When and Why. University of Nebraska-Lincoln Extension. EC145. http://extensionpublications.unl.edu/assets/pdf/ec145.pdf
2 Boyer, C., M. Stefanini, J. Larson, S. Smith, A. Mengistu and N. Bellaloui. 2015. Profitability and risk analysis of soybean planting date by maturity group. Agronomy Journal. 107:2253-2262. doi:10.2134/agronj15.0148
3 Gaspar, A.P. and S.P. Conley. 2015. Responses of canopy reflectance, light interception, and soybean seed yield to replanting suboptimal stands. Crop Sci. 55:377-385.
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