Taking Note of the Ending Reproductive Stages of Your Soybean Crop

Sep 02, 2020

By Jim Specht and Keith Glewen et.al.

The heat and drought in areas of the State are rapidly moving Nebraska’s 2020 soybean crop along. Growers have been asking how to determine late season growth stages for last irrigation of the season and for determining maturity. The following is an updated article from October 9, 2019. While we’re not anticipating a frost anytime soon, the original article also spoke about frost impacts.

Determining R7 Stage

R7 is defined as the calendar date when 50% (or all) of the field plants possess one mature pod. In most years, most leaves and pods will have changed color (from green to yellow-green or yellow) by this plant-based R7 date. On an individual pod basis, R7 occurs when the pod wall interior membrane ceases to cling tightly to the seeds and instead stays attached to the pod wall (as shown in Figure 1). This pod membrane status is an observable marker of soybean seed physiological maturity (i.e., no further increase in dry matter thereafter), and is effectively equivalent to black layer formation at the base of a corn kernel, a marker of corn seed physiological maturity (Nielsen, 2019).

Soybean stems typically turn brown shortly after R7 begins, though the stem can remain green due to an abnormally low pod/seed set. For a good review of the causes of green stem syndrome, see the article by Holshouser, 2009. Still, even then, dry matter gain in the seeds will have already ceased within any pod that has reached R7.

Key Points

The timing of the ending R stages in soybean is governed by planting date (PD) and varietal maturity group (MG), though the date of R7 can be hastened if water stress and high temperatures prevail in August.

Your varietal MG choice should reflect the actual planting date (early versus late). If you want the crop to avoid being impacted by a fall frost or freeze, the crop must attain the critical stage of R7 (physiological maturity) on or before the calendar date (for your location) of a 10% probability of a 32° F frost.
On an individual pod basis, physiological maturity occurs when the pod membrane no longer clings tightly to seeds in that pod (equivalent to how black layer indicates physiological maturity in corn).
You can use the online program SoyWater to project the probable in-field dates of the successive Vn and Rn stages in a soybean field.

Determining the R8 Stage

The final soybean stage is R8, which occurs when 95% of pods have attained maturity and have a variety-dependent color of brown or tan. Note that the date of the R8 stage is used by soybean breeders to establish/assign an MG number (e.g., 3.1) to each newly released variety. This is based on multi-site-year performance trials in which its R8 maturity date is matched with the R8 date of one of the known maturity-check varieties in those trials.

Seed moisture in a soybean pod undergoes a dry-down phase from about 60% at R7 to about 13% at R8. The rate and duration of this dry-down phase are governed by the daily degree of atmospheric evaporative demand, which is a function of solar radiation, humidity, temperature, wind speed, and soil surface moisture. In Iowa State University research studies, the dry-down period averages about 12 days, but can be faster or slower depending on coincident weather (Martinez-Feria et al. 2017).

Impact of Fall Frost/Freeze

Figure 1. Soybean pods collected from stage R7 plants (one mature pod per plant) that were opened to determine if the pod wall interior membrane was still clinging tightly to the seeds (leftmost pod), or if it was beginning to detach from the seeds (second pod), or if the membrane was now permanently attached to the pod wall (third pod). After attaining physiological maturity, seeds undergo a dry-down period from about 60% moisture to about 13% moisture (as shown in the left three pods). Note that the Rx.x numbers used here are pod-based stages, not plant-based stages.

Relative to the impact of a fall frost/freeze, the soybean stage of key importance is R7. Seed yield loss from a frost/freeze occurring on/after R7 will be limited to the fraction of pods on an R7 plant that have not yet reached a pod-based stage of R7 (as depicted by the second pod in Figure 1). However, if the frost/freeze occurs at stage R6 (full seed), the yield loss can be substantial, perhaps as much as 45-50%.

Using Crop Models in Soybean Staging

The calendar date of each sequential soybean vegetative (Vn) stage of main stem nodal development, and each successive reproductive (Rn) stage can be projected by most available soybean crop simulation models. The UNL-developed SoySim model (Setiyono et al., 2010) was shown to predict the dates of observed in-field Vn and Rn stages with minimal error (Torrion et al., 2011). Still, like other models, SoySim requires user input of current year and historical multi-year weather data, which is not an easy task for many soybean producers.

Another online program, UNL SoyWater, was developed (with funding from the Nebraska Soybean Board) for easy use by soybean producers to schedule seasonal irrigation events in a timely and water-efficient manner. This program automatically acquires daily (and historical) weather data from an automated weather data station closest to the producer’s field to reliably estimate daily/cumulative soybean water use via an evapotranspiration (ET) calculation. By embedding the SoySim model into the online SoyWater program, the weather data can now be used by SoySim to make Vn and Rn calendar date projections.

Producers can use SoyWater to project/track calendar dates for each Vn and Rn stage in a given soybean field and need only supply these four inputs:

the field's GPS location,
planting date,
variety maturity group (MG), and
field soil texture – selected from a map.

If you use SoyWater, you already know about its ability to reliably project calendar dates for seasonal progression of Vn and Rn stages in a soybean field. If not, click here to learn the steps needed to register for this free online program. (Approximately 1000+ producers have registered to date.) Then, you too can analyze the ending Rn stage dates for your 2019 fields.

See a related CropWatch article that details how SoyWater was used to project calendar dates of the Vn and Rn stages in 16 combinations of four planting dates with four varieties differing in maturity group (MG) in eastern Nebraska.

Source : unl.edu

Video: Moving Ag Research Forward Through Collaboration

BY: Ashley Robinson

It may seem that public and private researchers have different goals when it comes to agricultural research. However, their different strategies can work in tandem to drive agricultural research forward. Public research may focus more on high-risk and applied research with federal or outside funding, while private sector researchers focus more on research application.

“For me, the sweet spot for public private sector research is when we identify problems and collaborate and can use that diverse perspective to address the different aspects of the challenge. Public sector researchers can work on basic science high risk solutions as tools and technologies are developed. They then can work with their private sector partners who prototype solutions,” Mitch Tuinstra, professor of plant breeding and genetics in Purdue University’s Department of Agronomy, said during the Jan. 10 episode of Seed Speaks.

Public researchers they have the flexibility to be more curiosity driven in their work and do discovery research. This is complimentary to private research, which focuses on delivering a product, explained Jed Christianson, canola product design lead for Bayer CropScience, explained during the episode.

“As a seed developer, we worry about things like new crop diseases emerging. Having strong public sector research where people can look into how a disease lifecycle cycle works, how widespread is it and what damage it causes really helps inform our product development strategies,” he added.

It’s not always easy though to develop these partnerships. For Christianson, it’s simple to call up a colleague at Bayer and start working on a research project. Working with someone outside of his company requires approvals from more people and potential contracts.

“Partnerships take time, and you always need to be careful when you're establishing those contracts. For discoveries made within the agreement, there need to be clear mechanisms for sharing credits and guidelines for anything brought into the research to be used in ways that both parties are comfortable with,” Christianson said.

Kamil Witek, group leader of 2Blades, a non-profit that works with public and private ag researchers, pointed out there can be limitations and challenges to these partnerships. While private researchers are driven by being able to make profits and stay ahead of competitors, public researchers may be focused on information sharing and making it accessible to all.

“The way we deal with this, we work in this unique dual market model. Where on one hand we work with business collaborators, with companies to deliver value to perform projects for them. And at the same time, we return the rights to our discoveries to the IP to use for the public good in developing countries,” Witek said during the episode.

At the end of the day, the focus for all researchers is to drive agricultural research forward through combining the knowledge, skills and specializations of the whole innovation chain, Witek added.

“If there's a win in it for me, and there's a win in it for my private sector colleagues in my case, because I'm on the public side, it’s very likely to succeed, because there's something in it for all of us and everyone's motivated to move forward,” Tuinstra said.