As soybeans approach, reach and blow past the R6 or full
seed growth stage, it is worthwhile to take a moment to ponder what is
happening in the crop.
Even though soybeans will have flowers, pods and seeds
in various stages of development, all on the same plant, one can easily growth
stage a plant if after pods begin to develop one only pays attention to the
four uppermost nodes that house fully-expanded leaves.
R5.
Soybean plants that are at least halfway through the R5 or
beginning seed growth stage will have reached their peak in nitrogen fixation, number of leaf nodes, leaf area and height. As soybeans reach the full seed
growth stage, the nutrients they have accumulated in their leaves will peak and begin
the process of being redistributed to developing seeds (McWilliams et al.,
1999; Unknown, 2018). It takes an average of 15 days for soybeans to progress
from the R5 to R6 growth stages (Naeve, 2018).
R6.
The R6 stage is also referred to as the “green
bean” stage as at least one pod will contain a seed that fills the pod cavity
(remember this is a pod at one of the four uppermost nodes). Root growth will
cease about halfway through this growth stage. As long as leaves and pods remain
green, soybeans are still in the R6 growth stage (McWilliams et al., 1999;
Unknown, 2018). It takes 18 days on average for soybeans to progress from the
R6 to R7 growth stage (Naeve, 2018).
R7.
The beginning maturity (R7) growth stage is reached
when a pod on the main stem reaches its mature tan or brown color. This is a
particularly important milestone for soybeans to reach in the Upper Midwest as
soybeans at this growth stage are at less risk of yield loss due to frost. Seeds
have approximately 60 percent moisture at this growth stage and it takes an average of
9 days for soybeans to progress from the R7 to R8 growth stage (McWilliams et
al., 1999; Unknown, 2018; Naeve, 2018).
R8.
At the R8 or full (physiological) maturity growth
stage, fewer than 5 percent of pods will remain neither tan nor brown. Now is
the time to begin checking soybean moisture levels as warm and dry weather can
mean that seeds will fall below harvest moisture (15%) in less than 2 weeks
time. Dropping moisture levels lower
(down to 13%) is recommended for longer-term storage, but as farmers are paid at
the elevator by weight, leaving beans in the field to dry to lower than optimal
moisture levels can result in income losses (McWilliams et al., 1999; Unknown,
2018).
References & Other Resources.
McWilliams, D.A., Berglund, D.R. and Endres, G.J. 1999. Soybean
growth and development quick guide. Online.
A-1174. NDSU Extension Service. North Dakota State University. Fargo, ND. {Accessed
Sept 2, 2020}
Naeve, S. 2018. Soybean growth stages. Online.
UMN Extension. University of Minnesota. St. Paul, MN. {Accessed Sept 2, 2020}
Unknown. 2018. A visual guide to soybean growth stages. Online.
Nutrient and Pest Management Program. University of Wisconsin Extension,
College of Agricultural and Life Sciences. Madison, WI. {Accessed Sept 2, 2020}
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