Amplifying Positive Impacts of Early Soybean Planting

Soybean fields in planting date study at UNL's East Campus — Planting date studies conducted on UNL's East Campus showed yield decreases of 1/4 bu/ac (2003) and 5/8 bu/ac (2004) for each day after May 1 that soybean were planted.

April 19, 2018

James Specht - Emeritus Professor of Agronomy

Patricio Grassini - Professor of Agronomy and Horticulture, and Cropping Systems Specialist

Nathan Mueller - Former Extension Educator

Roger Elmore - Emeritus Extension Cropping Systems Agronomist

Juan Ignacio Rattalino Edreira - Research Assistant Professor of Agronomy and Horticulture

Data continues to suggest growers are planting soybean earlier than ever before. In fact, over the past three decades, farmers have persistently shifted average soybean planting dates in the North Central U.S. to earlier calendar dates at a rate of ½ day per year (Specht et al., 2014). A study surveying soybean growers throughout the north central U.S. in 2014-2015 looked at factors that influenced soybean yields. Survey data of 3,568 field-year observations from rainfed and irrigated soybean fields found planting date to be the most consistent management factor increasing soybean yield (Rattalino Edreira et al., 2017, Mourtzinis, et al. 2018).

Data from Nebraska, Iowa, South Dakota, Illinois, Indiana, Wisconsin and Ohio all show increased yields from earlier planting of soybean. Grower-reported yield data for southern and northern Nebraska in both irrigated and non-irrigated environments also shows the benefit of earlier soybean planting [and the yield penalty for delaying planting after May 1 (Figure 1)].

Key Points

Planting soybean early is critical to maximizing yield. This has been found through numerous University studies in addition to grower-reported data.
The relationship between maturity group and early soybean planting is not clear. Perhaps what is more important is looking at specific variety performance for varieties adapted for your area rather than selecting a specific maturity group.

Graph of yields based on various soybean planting dates — Figure 1. Soybean yield versus planting date in southern (left) and northeast (right) Nebraska. Southern Nebraska includes south central and southeast regions because these two regions exhibited a similar yield response to planting date delay. The planting date range is shown relative to May 1. Each data point represents an individual field-year observation. Yellow and blue symbols indicate non-irrigated and irrigated fields, respectively. The dashed line represents the yield potential response to planting date delay after May 1. From the data it appears that non-irrigated fields are less responsive to planting date in southern Nebraska.

When soybean planting is delayed beyond April 30, the crop is denied access to early spring solar radiation (Figure 2, dark grey area). The germination to V1 phase is shorter with a warmer planting date, but V1 is still delayed, thus delaying the V1 start of the phyllochron (period of sequential leaf emergence). Note that a 48-day planting delay from April 30 to June 17 led to respective R7 (physiological maturity) dates of 135-156 days after April 30. This 21-day difference resulted in 27 fewer days for Vn to Rn development in the late planting. The 48-day spread over the four planting dates did not delay very much the number of days for the crop to reach stage R8 (when 95% of all pods are mature), which was discussed in a prior CropWatch article. Main stem node accrual ceases at R5 irrespective of the planting date, so plants in later plantings will have fewer nodes, and more importantly, fewer nodal leaves available for photosynthetic-driven seed-filling. Note that the V1 to R1 stage seems to be a constant 28-32 days despite the two-week spread in the successive planting dates. This timeframe applies to the MG 3.0-3.9 varieties used in this study and may be slightly less in MG 2.0- 2.9 varieties, but those were not studied here. Floral induction occurs at the V0 to V1 stage period, no matter the planting date. Once the calendar date of R1 is established in each planting date, the remaining R stages seem to be shortened to some degree when the planting date is successively delayed.

The yield benefit for planting soybean early is well established and documented. The question, perhaps in part from the data in Figure 2, now becomes: How does one amplify the positive impacts of early soybean planting? Recently growers have asked what maturity group should be used with early planting and if there’s a yield difference for early planting in irrigated versus non-irrigated environments.

Delayed soybean planting date chart — Figure 2. Early, mid-, late May and mid-June planting dates averaged over 14 varieties (MG 3.0 to 3.9) show the difference in days between 0 (PD), V1, R1, etc. The dark grey area at the figure bottom indicates the number of days of spring solar radiation that a late-planted crop cannot capture (up to 48 days lost with a mid-June planting!). The fact that warmer soil temps with later planting date allow a shorter planting date to V1 phase still does not allow the crop to catch up. Note that not all of the growing season was used when the same varieties were planted earlier versus later, so it could be reasonable to postulate a later MG would be better in earlier planting dates, but we lack the answer for that from this data. You can see the difference in the timing of R7 in the four planting dates.

Maturity Group Considerations in Irrigated and Non-Irrigated Environments

Graph showing results of soybean planting date study — Figure 3. Soybean yield in each of six planting dates in an irrigated experiment conducted at the UNL East Campus in Lincoln in 2015 for two varieties (MG2.1 and MG3.0). A linear regression analysis indicated that the regression coefficients (i.e., slopes), reflect the reduction in seed yield that occurred per day of delay in planting date for each variety.

A study conducted at UNL’s East Campus compared a 2.1 and a 3.0 maturity group variety at 10-day intervals from April 23 through June 19. This was conducted in 2015 in an irrigated environment. Yield was highest for early-planted soybean with a yield penalty of 1/8 to 1/4 bu/ac per day of delay in planting for MG2.1 and MG3.0 varieties, respectively. The study also indicated that yield of the MG3.0 variety was higher relative to the MG2.1 variety in early plantings (late April and early- to mid-May), but the opposite (greater yield in MG2.1 versus MG3.0 variety) was found for late plantings (late-May and June) (Figure 3).

Producer responses to a survey on their choice of maturity group for irrigated versus rainfed fields can be seen in Figure 4. Producers in northeast Nebraska, on average, plant MG2.6 in irrigated fields but 2.8 in rainfed fields, whereas in southeast Nebraska, producers plant MG3.1 in irrigated fields and 3.3 in rainfed. In general, it appears from these data that Nebraska soybean producers use earlier MG varieties in their irrigated fields than in their rainfed ones. Extension Educators have also observed the use of earlier MG (<3.0 varieties) in irrigated fields and longer MG (>3.0) for non-irrigated fields (in southern Nebraska). While this may seem counter-intuitive, the shorter MG for irrigated fields in southern Nebraska may be due to several reasons:

High yielding MG2.4-2.5 genetics.
Earlier MG helps with earlier harvest to help spread out harvest and risk.
Early harvest for other goals such as longer window for cover crop growth planted into soybean residue, etc.

Eastern and southeastern Nebraska farm reports on soybean maturity group

Non-irrigated soybean maturity groups planted in Nebraska

Figure 4. Nebraska producer responses to survey on soybean maturity group planted for irrigated (left) and rainfed (right) systems, collected as part of a larger survey conducted from 2013-2015 in the north central U.S. representing 909 fields, 89% of which were irrigated and 11% of which were rainfed. The line represents a very generalized suggested but not prescriptive divider between MGII (above) and MGIII (below).

The advantage of a longer MG for non-irrigated fields may be due more to water deficits that can occur during seed-fill in many years and at many locations throughout Nebraska. Late-season soil water deficits can create stress that hastens physiological maturity (R7), resulting in reduced yield. Planting these rainfed fields to longer MG can potentially shift the crop’s seed-filling timeframe to somewhat later in the growing season when the temperatures are typically lower and allow the crop more time to catch a drought-mitigating rain.

Variety Selection for Proven Yield Performance Critical Too

Third-party variety trials conducted (Figure 5) in eastern Nebraska this decade reveal that picking a variety for proven yield performance is one of the most critical yield drivers. There were top-yielding varieties across a range of relative maturities. The relative maturity of a variety explained very little of the variation in yield within a growing season. When selecting varieties first focus on proven yield performance in your region, then evaluate the relative maturity of your selections for planting order and field assignments.

Chart of soybean planting date maturity groups planted in northeast Nebraska

Chart of soybean maturities planted in eastern Nebraska

Figure 5. Soybean variety trial data conducted by FIRST Seed Tests at multiple locations per year 2012-2016 in both northeast and southeast Nebraska.

Summary

Planting soybean early is critical to maximizing yield. This has been found through numerous University studies in addition to grower-reported data.
The relationship between maturity group and early soybean planting is not clear. Perhaps what is more important is looking at specific variety performance for varieties adapted for your area rather than selecting a specific maturity group.

Growers still may choose not to plant soybean early due to a number of factors including: equipment constraints, tradition of planting corn prior to soybean, and weather constraints during planting. There also may be an overestimation of risk associated with seed chilling injury, early frost, and seed and/or plant stand loss associated with early planting. Ways to work around these constraints can include hiring someone to custom plant soybean at the same time as corn planting, using fungicide/insecticide seed treatments, assessing soil temperatures, and testing earlier soybean planting dates for oneself.

We have minimal data from throughout the state looking at maturity group differences with early planting dates in both irrigated and rainfed environments. If you’re interested in comparing this for yourself, consider using the Nebraska On-Farm Research Protocols.

References

Bastidas, A. M., T. D. Setiyono, Achim Dobermann, Kenneth G. Cassman, and Roger Wesley Elmore. Soybean Sowing Date: The Vegetative, Reproductive, and Agronomic Impacts. Crop Science 48:727–740.

Conley, Shawn. 2018. Soybean planting date and maturity group considerations moving into 2018. Wisconsin Extension Cool Bean. http://coolbean.info/2018/04/09/planting-date-and-maturity-group-considerations-moving-into-a-potentially-early-spring-2018/

Grassini, Patricio, Jennifer Rees, Nicolas Cafaro La Menza, and James Specht. 2016. What does it take to produce 80+ bu/ac soybean? Nebraska Extension EC3000. http://extensionpublications.unl.edu/assets/pdf/ec3000.pdf

Iowa State University. Soybean planting date can have a significant impact on yield. ISU Integrated Crop Management. https://crops.extension.iastate.edu/soybean-planting-date-can-have-significant-impact-yield

Jasa, Lisa. 2009. Adjust Maturity with Early Planted, Rainfed Soybeans. Nebraska Extension CropWatch. https://cropwatch.unl.edu/adjust-maturity-early-planted-rainfed-soybeans

Lindsey, Laura. 2017. Soybean planting date, row width, and seeding rate recommendations. Ohio State University Extension Agronomic Crops Network. https://agcrops.osu.edu/newsletter/corn-newsletter/2017-09/soybean-planting-date-row-width-and-seeding-rate-recommendations

Mourtzinis, Spyridon, Juan I. Rattalino Edreira, Patricio Grassini, Adam C. Roth, Shaun N. Casteel, Ignacio A. Ciampitti, Hans J. Kandel, Peter M. Kyverga, Mark A. Licht, Laura E. Lindsey, Daren S. Mueller, Emerson, D. Nafziger, Seth L. Naeve, Jordan Stanley, Michael J. Staton, Shawn P. Conley. 2018. Sifting and winnowing: Analysis of farmer field data for soybean in the US North-Central region. Field Crops Research 221:130-141

Mueller, Nathan, Roger Elmore, and Troy Ingram. 2017. Large Check, Small Seed, Significant Impact. Nebraska Extension CropWatch. https://cropwatch.unl.edu/2017/Large-Check-Small-Seed-Significant-Impact

Mueller, Nathan, Aaron Nygren, Jenny Rees, and Jim Specht. 2016. Adjusting for Delayed Soybean Planting. Nebraska Extension CropWatch. https://cropwatch.unl.edu/2016/adjusting-delayed-soybean-planting

Nafziger, Emerson. 2017. Planting date for corn and soybeans in Illinois. University of Illinois the Bulletin, http://bulletin.ipm.illinois.edu/?p=3848

Scoop on Soybean Blog. 2018. Early does it: Optimal soybean yields come with timely planting. South Dakota Soybean Association. https://www.sdsoybean.org/scoop-on-soybean-blog/early-does-it-optimal-soybean-yields-come-with-timely-planting/

Specht, James E., Jennifer M. Rees, Gary L. Zoubek, Keith L. Glewen, Brandy S. VanDeWalle, James W. Schneider, David L. Varner, and Allan R. Vyhnalek. Soybean planting date: When and Why? Nebraska Extension EC145. http://extensionpubs.unl.edu/publication/9000016368318/soybean-planting-date-when-and-why/

Specht, James E. and Thomas Hoegemeyer. 2017. Nebraska Soybean and Corn Pocket Field Guide, 2017 Edition.

Tenorio, Fatima Amor, P. Grassini, J. Rees, K. Glewen, N. Mueller, L. Thompson, and J. Specht. 2016. Early Bird Gets the Worm: Benefits of Early Soybean Planting. Nebraska Extension CropWatch. https://cropwatch.unl.edu/2016/early-bird-gets-worm-benefits-early-soybean-planting

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Soybean