How many have heard the phrase, ‘the soybean crop will be made in August?’ Many have encountered this through neighboring farmers, people in the ag industry, and on ag media. Many in the past and currently still do not plant soybeans till mid- to late-May, while others plant soybeans in early May or late April, such as large farms that need more time to complete planting acres. Soybean planting in the final week of April can happen based on better hybrids, seed treatments of fungicide and insecticide, and soil temperatures being more receptive to early planting, to go along with the benefits of earlier planted soybeans. Is this phrase still relevant in 2022?

The best way to test if this phrase is still justified is to use three different planting dates and then calculate the date using the average number of days between stages. The guide for this example can be found on the University of Minnesota website. In these examples, the plants were taken to V7 prior to R1 for a reason, as the earlier planted soybeans would be triggered by the longer days and shorter nights because of the coming summer solstice that will prompt them to flower. Two weeks separated each planting date, with all dates falling between traditional Illinois soybean planting dates.

First Example                                     Second Example                                Third Example

Planting Date                                      Planting Date                                      Planting Date

4/30                                                     5/14                                                     5/30

Planting to VE (Emergence) – Average of 10 days between stages

5/1-5/10                                              5/15-5/24                                            6/1-6/9

VE to VC – Average of 5 days between stages

5/11-5/15                                            5/25-5/29                                            6/10-6/14

VC to V1 – Average of 5 days between stages

5/16-5/20                                            5/30-6/3                                              6/15-6/19

V1 to V2 – Average of 5 days between stages

5/21-5/25                                            6/4-6/8                                                6/20-6/24

V2 to V3 – Average of 5 days between stages

5/26-5/30                                            6/9-6/13                                              6/25-6/29

V3 to V4 – Average of 5 days between stages

5/31-6/4                                              6/14-6/18                                            6/30-7/4

V4 to V5 – Average of 5 days between stages

6/5-6/9                                                6/19-6/23                                            7/5-7/9

V5 to V6 – Average of 3 days between stages

6/11-6/14                                            6/24-6/28                                            7/10-7/14

V6  to V7 – Average of 3 days between stages

6/15-6/17                                            6/29-7/1                                              7/15-7/17

V7 to R1 – Average of 3 days between stages

6/17-6/20                                            7/2-7/4                                                7/18-7/20

R1 to R2 – Average of 3 days between stages

6/21-6/23                                            7/5-7/7                                                7/21-7/23

R2 to R3 – Average of 10 days between stages

6/24-7/3                                              7/8-7/17                                              7/24-8/2

R3 to R4 – Average of 9 days between stages

            7/4-7/12                                              7/18-7/26                                            8/3-8/11

R4 to R5 – Average of 9 days between stages

            7/13-7/21                                            7/27-8/4                                              8/12-8/20

R5 to R6 – Average of 15 days between stages

            7/22-8/4                                              8/5-8/19                                              8/21-9/4

R6 to R7 – Average of 18 days between stages

8/5-8/12                                              8/20-9/6                                              9/5-9/22

Each stage of soybean is crucial and can make or break yield, but four-stages are especially critical to yield in soybeans, and those stages are between R3-R6. R3 stage plants are beginning to flower “Typically, 60 to 75 percent of flowers abort, but stress can increase the loss. Temperature or moisture stress can limit pod numbers, beans per pod, or bean size (Pioneer, 2019 R3).” R4 stage plants are when the plant is at full pod “This is the most crucial stage for seed yield……. The pods are filling at a maximum rate, making the plant most susceptible to stresses and causing it to move nutrients from other areas weakening it to invasion by diseases through the roots and foliage (Pioneer, 2019 R4).” R5 stage plants are begging for seed “Seed filling requires water and nutrients…… At R5, the plant is less able to compensate for stresses (Pioneer, 2019 R5).”  R6-R8 are faintly less critical stages for soybeans because in soybean stage R6 the pod is full of seeds, so weather stresses such as extreme heat and rain have less effect.

In the table with three planting dates, one can observe that the earlier planted soybeans’ critical stages are in July and early August, with the more traditional planting dates falling more in the August timeline. For the past three years on our farm, this has been on my mind, thinking the timeline has shifted based on our earlier planting dates. The past few Augusts have been hot and dry on our farm, yet we still produced above-average yields, so this always made me wonder if we were beating that August timeline. Like everything in farming, the timing of rains and avoiding lengthy and extreme hot-dry conditions in that R3-R6 time will influence soybeans greatly. After further review, the phrase holds but is based on what date soybeans are planted.

Sources

Naeve, S. L. (n.d.). Soybean growth stages. UMN Extension. Retrieved August 11, 2022, from https://extension.umn.edu/growing-soybean/soybean-growth-stages#herbicides%3A-how-growth-stage-affects-applications-539863

Pioneer. (2019, April 26). R3 soybean growth stage: Beginning pod development. R3 Soybean Growth Stage: Beginning Pod Development | Pioneer Seeds. Retrieved August 11, 2022, from https://www.pioneer.com/us/agronomy/r3-stage-beginning-pod-development.html

Pioneer. (2019, April 26). R4 Soybean Growth Stage: Full pod. R4 Soybean Growth Stage: Full Pod | Pioneer Seeds. Retrieved August 11, 2022, from https://www.pioneer.com/us/agronomy/r4-stage-full-pod.html#:~:text=At%20R4%2C%20the%20plant%20reaches%20the%20full%20pod,In%20hot%2C%20dry%20conditions%2C%20consider%20irrigation%20if%20available.

Pioneer. (2019, April 26). R5 soybean growth stage: Beginning seed. R5 Soybean Growth Stage: Beginning Seed | Pioneer Seeds. Retrieved August 11, 2022, from https://www.pioneer.com/us/agronomy/r5-stage-beginning-seed.html#:~:text=At%20R5%2C%20the%20plant%20is%20less%20able%20to,maximum%20height%2C%20number%20of%20nodes%20and%20leaf%20area.