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									Crop Update Newsletter Prepared By:
Todd Vagts, ISU Extension Crops Specialist
Serving northwest Iowa

In this issue
 Most corn and soybeans reach physiological                                    Calibrating your yield monitor
    maturity                                                                    Recent developments in plants and
 How to determine soybean maturity                                              intellectual property rights
 On-farm storage of soybeans

Harvest has begun in some early maturing (seed) corn and soybean fields. Before we know it, much of
the area’s crop will be out of the field and in grain bins. Soybean harvest and storage can often be a
challenge because of the way the plant and pods mature and dry down. Identifying key stages in the
maturity and dry-down process can help to schedule harvest activities. Remember that soybeans need to
be at 13% moisture or less for safe storage. For those that have yield monitors in combines, the
information generated by the devices is no good unless the yield monitor is properly calibrated. Spend
the extra time to get the device working properly so that you will trust the data this winter in your
management decisions.

Growing Degree Day Accumulation and Crop Development
The area picked up 99 degree days last week, a                                        Figure 1. GDD Acccumulation (9/16)
much more normal accumulation when compared          2800
to the previous week (Figure 1). Degree-day                                            Physiological maturity = 2600 DD
accumulation will continue to slow as the next 7-
day total is predicted to be 71. According to
degree-day accumulations, much of the corn and
                                                      Accumulated DD50's

soybean crop has advanced past the physiological     2700
maturity mark. I’ve noticed a few fields of both
corn and beans that have bean taken out of the       2650
field. (Physiological maturity is the point in which
maximum dry weight accumulation has occurred
                                                     2600                              ----------------Physiological Maturity----------------
in the grain.) Total degree day accumulation
remains on track with last year’s accumulation for
this calendar date and is still well above (200 DD)  2550
the 12-year average.
Determining soybean maturity
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Determining when soybeans are mature (both














physiological and harvest maturity) helps to

                                                                                                      Planting Date
schedule harvest operations and reduces in-field
harvest losses. Physiological maturity is when the                                      North                    7-Day Forecast (north)
soybean has accumulated its maximum dry
weight. The growth stage classification is R7 - R8.

With an indeterminate soybean, all pods will not reach physiological maturity at the same time. There is
a period of about two to three weeks from the time the 1st pod reaches physiological maturity to the last
pod reaching physiological maturity. The average seed moisture at the time the pod is physiologically
mature is 55%. When all pods on the soybean plant have reached physiological maturity, the average
seed moisture for the plant is usually around 44%.

Two main indicators can be used to determine when individual pods reach this stage.

                                             Volume 2, No. 25
Crop Update Newsletter Prepared By:
Todd Vagts, ISU Extension Crops Specialist
Serving northwest Iowa
 Pod Color: A short time prior to seed shrinkage, the pods will begin to lose their green color and will
  take on a yellowish cast. When the pod is completely free of green, the seeds inside have already
  started to shrink.
 Seed Shrinkage: Once the seed has attained its maximum dry weight and size, it will begin to shrink.
  Upon shrinking, the seed will become less associated with the white membrane surrounding the seed.
  Eventually, the membrane will no longer cling to the seed and will stay with the pod wall when split

Harvest maturity indicates when all beans on the soybean plant are ready to be harvested. This is usually
when the average seed moisture is 13%. Harvest maturity is usually reached about one to two weeks after
the entire plant has reached physiological maturity, depending on temperature and humidity. Timely
harvest of a mature field will help minimize losses due to shattering and decreased seed quality.

On-farm storage of soybeans
Storage of soybeans on-farm requires some special considerations when compared to corn. As with most
grains, when moisture is too high, spoilage and reduced germination will result. High oil content of the
soybean makes them more susceptible to spoilage than corn; therefore soybeans need to be about two
points dryer than corn for proper storage. For winter storage, store commercial soybeans at 13 percent
moisture or less. Soybeans with less than 15 percent moisture can be dried with bin fans.

Aerate the stored soybeans to maintain grain temperature at 35 to 40 degrees F in winter and 40 to 60
degrees F in summer. Check the bins regularly for heating or spoilage. When drying soybeans in high or
low temperature dryers, be careful. Soybeans are fragile and can be damaged by air that is too hot or too
dry, as well as by rough handling. Soybeans have about 25 percent less airflow resistance than shelled
corn; fans sized for corn drying will produce greater airflow through soybeans. Greater airflow means
faster drying.

Calibrate your yield monitor correctly
University of Nebraska Engineer Paul Jasa recommends proper calibration of yield monitors. When
properly calibrated, a yield monitor can be a valuable tool to gather information about crop production,
providing on-the-go estimates of yield and grain moisture content. Jasa further explains that a yield
monitor consists of several sensors and a small computer to integrate, display, and save the information.
On most yield monitors, the grain flow through the combine is estimated by measuring the force the grain
exerts on a sensor at the top of the clean grain elevator. The greater the grain flow, the greater the force or
displacement measured. The area harvested is determined from the measured travel speed and the known
width of cut. Grain moisture content is also measured so that the grain yield can be corrected to a standard
moisture content and estimated on a per acre basis.

Proper calibration involves weighing the grain in a load using a scale and measuring the moisture content
with a standard moisture tester. These numbers are entered into the yield monitor's computer, allowing the
computer to assign mass flow rates and moisture contents to the millivolt readings sensed. This
calibration must be performed separately for each crop. A Checklist for Yield Monitor Operation and
Calibration can be found at the Ohio State University web site at Jasa’s full article in the University of Nebraska
September 14, 2001 Cropwatch can be accessed online at

Plants and Intellectual Property Rights (Ray Massey, University of MO)
There have been several developments in intellectual property rights related to plants over the last 2 years.
The article at this web address ( briefly notes
the current laws regarding plants and intellectual property rights and recent court cases, along with their

                                               Volume 2, No. 25
Crop Update Newsletter Prepared By:
Todd Vagts, ISU Extension Crops Specialist
Serving northwest Iowa
For further information pertaining to this newsletter; please contact me or any of the county extension offices. This
newsletter can also be accessed on-line at If you
would like this letter to be emailed directly to you, please send an email with the desired email address to

Todd Vagts
Iowa State University Extension
Field Specialist, Crops

1240 D. Heires Avenue           Office: 712-792-2364
Carroll, IA 51401               Cell:    712-249-6025
Email:        Fax: 712-792-2366
Web Page:

Provided to you by:


                   Iowa State University and U.S. Department of Agriculture cooperating

Extension programs are available to all without regard to race, color, national origin, religion, sex, age or


                                                  Volume 2, No. 25

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