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Serving: IA

Get ready for soybean harvest

TAGS: Harvest
Rod Swoboda Soybean field with farm in background
START OR WAIT? Many agronomists believe waiting until soybeans reach 13% moisture before starting harvest could lead to higher shatter loss.
Soybean Source: Prepare to handle difficult situations with wind damage, varying maturity and other challenges.

If there was ever a vote on a year that folks would like to get a “do over” on, 2020 would be a leading candidate. Since we can’t vote 2020 away, we keep grinding away at it a day at a time. And it won’t be too much longer before it will be time to start soybean harvest.

Given the year we’ve had, I have a feeling there will be more than just teeth grinding as we enter bean fields that have suffered a long list of challenges from drought to pest damage, and for a third of Iowa or more, damage from the derecho windstorm. Here are some things to consider as we head into fall and beans start to mature.  

Scout for storm damage

Many are asking if soybeans will recover from storm damage. There isn’t a one-size-fits-all answer, but in general, beans will recover better than corn in hard-hit areas. A fair number of bean fields I’ve seen post-storm have straightened up to varying degrees, but that doesn’t always tell the whole story. Some scouting is needed to see if there was much permanent damage from the winds and any accompanying hail. Even if no hail was involved, a good resource is our own soybean hail guide at store.extension.iastate.edu. Look out for these problems when scouting:

Defoliation. Fields likely suffered some level of defoliation or stand loss from the storm, so the charts in the hail guide can be used to gauge potential yield impacts. For example, yield loss from reproductive stage stand loss is equivalent to the percentage of dead plants. In other words, if you had a 5% reduction in plant population, that equals a 5% loss in yield potential in that field. 

With defoliation, as soybean growth progresses to the reproductive stages, potential yield reduction from defoliation increases. Defoliation caused by hail or wind results in a reduction of the plant’s ability to perform photosynthesis.

Defoliation is estimated by looking at each trifoliate leaf on 20 plants, determining percent missing tissue for each and then calculating an average value for percent missing tissue per plant. When estimating, remember defoliated tissue includes both missing tissue and that which is still attached but dead. Do not count tissue that is still green as defoliation, even if it seems injured. 

Lodging. Lodging can cost yield even if the plants aren’t broken off or haven’t lost a lot of leaf area from the wind or hail. It is challenging to find a lot of info on the impact of lodging on soybean yields, but while I was researching, I came across a helpful article written by David Holshouser from Virginia Tech, “Lodging and its effect on soybean yield.” He wrote the article in 2015 in anticipation of hurricane damage. Unfortunately, the concepts fit for the derecho winds we had as they were hurricane force.  

He talks about restriction of maximum physiological development that can occur from lodging, which reduces photosynthesis in the upper, more productive leaves. He also mentions that harvest loss from lodging can range from 3% to 10%. The article can be found at mssoy.org

Harvesting issues this fall 

Lodged bean plants or green stems are a nightmare to harvest, and there are entire sections of combine operator manuals and university articles that go into great detail about how to tackle these issues. Without going into a lot of detail, here are some highlights to consider as we prepare for bean harvest:  

  • Position the cutter bar as close to the ground as possible.  
  • Decrease ground speed to 2.5 to 3 mph.  
  • Move the reel axle forward so it’s 9 to 12 inches ahead of the cutter bar.  
  • Angle pickup fingers on the reel back slightly to more aggressively pull lodged plants to the cutter bar. Reduce the angle of the fingers if the plants are riding over the top of the reel.  
  • Operate reel as low as necessary to pick up lodged plants without causing them to ride over the top of the reel.   
  • For plants lodged in one direction, harvest them in the opposite direction they’re leaning.  
  • Use a reel speed about 10% to 25% faster than ground speed (up to 50% faster if crop lodged badly).  
  • Complete the harvest as quickly as possible after beans reach 13% moisture. Damage and losses can increase at lower moisture content as well as at excessive moisture.  
  • Make one adjustment at a time and stop frequently to evaluate how your tactics are working.  

It’s easier said than done, of course, but don’t let those beans get too dry in the field, which can increase yield loss to shatter and decreased overall weight as we dip below 13% soybean moisture content. A University of Nebraska study indicates it’s worth an additional $10 to $12 per acre harvesting at 13% as opposed to 11% moisture.  

While it hasn’t been a very fun growing season, let’s hope that the weather cooperates, and we have a quicker-than-average (and safer-than-average) harvest. 

McGrath is the Extension coordinator for the Iowa Soybean Research Center at ISU. Email cmcgrath@iastate.edu

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