Impact of Late Planting on Soybean Yield in Southern Illinois

Background and Objectives

  • Many growers are sometimes faced with the decision to plant soybeans at very late dates during the growing season.
  • Yield of late-planted soybeans can be impacted by the shortened growing season, dry soil conditions, or freeze injury.
  • Delays in planting caused by unfavorable weather in 2015 and 2019 in Southern Illinois provided the opportunity to observe the effect of late planting on soybean yield.
Late planted soybean showing freeze symptoms.

Study Description

  • Surveys were conducted of late-planted soybean locations in Southern Illinois in 2015 and 2019.
    • - 2015: 158 fields planted between July 15 and August 17
    • - 2019: 237 fields planted between July 1 and July 20
  • Grower location, soybean maturity, planting date, planting rate and grain yield data were collected.



  • Yield declined with increasingly late planting dates and dropped off sharply when planting was delayed into August (Figure 1).
  • Yield declined an average of 1.3 bu/acre per day when planted after July 15 (Figure 2).
  • Soybeans planted in August suffered freeze injury at several locations, which resulted in significantly reduced yield or no yield in some cases.
Soybean yield grouped by planting date range. Means with different letters were significantly different at P less than 0.001.

Figure 1. Soybean yield grouped by planting date range. Means with different letters were significantly different at P <0.001.

Linear regression of soybean yield on planting date among 158 grower fields in Southern Illinois, 2015.

Figure 2. Soybean yield response to late planting among 158 grower fields in Southern Illinois in 2015.


  • Late-planted soybean locations spanned a smaller range of planting dates in 2019 than 2015, from July 1 to July 20.
  • Soybean yield declined by an average of 0.3 bu/acre per day of delayed planting over this time period (Figure 3).
  • Within the planting date range that 2015 and 2019 locations overlapped - July 16 to July 20 - yields were similar, averaging 37.2 bu/acre in 2015 and 39.6 bu/acre in 2019.
  • Locations planted with maturity group 4.0 and shorter soybean varieties yielded less than longer-season varieties with both early-July and mid-July planting (Figure 4).

Authors: Eric Alinger, Pioneer; Emerson Nafziger, University of Illinois
May 2020

The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. 2015 and 2019 data are based on average of all comparisons made in over 395 locations through Dec 1, 2019. Multi-year and multi-location is a better predictor of future performance. Do not use these or any other data from a limited number of trials as a significant factor in product selection. Product responses are variable and subject to a variety of environmental, disease, and pest pressures. Individual results may vary.