Yield Components Drive Decisions

Yield Components Drive Decisions

Improve one or two management practices to reap more bushels yet this season

You can’t just plant and harvest a soybean crop, leaving it to fend for itself in between. With that mindset, you’ll miss out on untapped yield potential, according to Farm Journal Associate Field Agronomist Missy Bauer. Even though it’s almost July, you still have time to increase yields, she says.

The bulk of soybean yield is determined during the reproductive growth stages. However, soybeans, specifically indeterminate varieties, respond to management practices and environmental factors from emergence through R6. 

Soybean yields are made up of three components: total number of pods, number of beans per pod and weight per bean (seed size).

“Large yield increases are the result of increased pods per plant,” Bauer explains. “The upper limits on beans per pod and seed size are genetically set; together, they can make a sizable difference.”

Of the three yield components, Bauer says farmers do the best job of influencing seed size, mainly through the strategic use of fungicides and insecticides when thresholds have been met. The Farm Journal Test Plots have found when controlling foliar diseases and insects, once thresholds have been exceeded, the resulting yield improvement can often be attributed to an increase in seed size. 

Protecting seed size can influence soybean yields by as much as 10 bu. to 15 bu. per acre. However, Bauer believes the upper limit on seed size and the potential number of beans per pod are genetically set and won’t budge much beyond what genetics will allow.

The majority of yield gains farmers stand to capture in the future will likely come from increased pods per plant, Bauer says.

One of the challenges when trying to increase pods per plant is flower and pod abortion. Soybeans abort between 60% and 75% of all flowers each season, which are unable to contribute to yield.

“About half the abortion occurs before the flowers develop into young pods, while the other half occurs as a result of pod abortion,” Bauer says. Currently there is no specific practice to help reduce pod abortion.

Once soybeans reach flowering (R1), you want to minimize stress from factors such as insects and disease, if possible, to prevent yield loss. For instance, stress occurring at:

  • R1 through R4 can reduce the number of the pods each plant produces.
  • R3 through R4 can reduce the size of pods.
  • R4 through R6 will cause beans to abort within the pod. 
  • R5.5 to R6.5 can reduce the size of the seed.

Along with knowing the vegetative and reproductive stages and how they impact growth and development, Bauer says it’s important to understand how a soybean works inside the canopy.

Photosynthesis in soybeans is influenced by carbon dioxide (CO2) entering the plant through openings called stomata. When stomata close, the photosynthesis rate decreases. Heat and moisture stress cause stomata to close.

“This can happen to the degree the plant will run backward; it burns up its energy inside,” Bauer explains. “This happens to soybeans if we have a hot environment, and they don’t have an opportunity to cool before the sun goes down.”

CO2 levels in the canopy might influence soybean yields, which means row spacing, plant population and plant height come into play. 

Addressing each yield component throughout the season can be an overwhelming process to begin. Start with small steps, Bauer encourages.  

“Improve one or two management practices this year, and you’ll be on your way to higher yields. 

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