Minimize stress during reproductive stages
Plant them and forget them used to be a common philosophy for soybean growers. Not anymore. Today, with favorable prices in place for 2014, farmers are looking for ways to manage their soybeans throughout the season to increase bushels.
Once soybeans reach flowering, you want to minimize stress as much as possible
A good place to start is by knowing the soybean yield components and how each one influences yield, notes Missy Bauer, Farm Journal Associate Field Agronomist.
Bauer addressed soybean vegetative growth and development in the March issue of Farm Journal. This article addresses some of the practices you can implement—or avoid—to boost bean development during the reproductive stages. These stages are critical as soybeans finalize their total number of pods per plant, number of beans in the pod and bean weight.
Of the three yield components, she notes that farmers do the best job today of influencing seed size, mainly through the strategic use of fungicides and insecticides when thresholds have been met. Plot data has shown when controlling foliar diseases and/or insects, once thresholds have been exceeded, the resulting improvement in yield can often be attributed to an increase in seed size. Protecting seed size can influence soybeans yields as much as 10 bu. to 15 bu. per acre. However, she believes that the upper limit on seed size, as well as 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 that farmers could capture will likely come from increased pods per plant, she says.
The impact of stress.
Once soybeans reach flowering (R1), you want to minimize stress, if possible, to prevent yield loss. For instance, stress that occurs from R1 through R4 can reduce the number of the pods each plant produces. Stress at R3 through R4 can reduce the size of the pods. Stress at R4 through R6 will cause the beans to abort within the pod, while late stress at R5.5 to R6.5 can reduce the size of the seed itself.
Along with knowing the vegetative and reproduction stages and how they impact growth and development, Bauer says farmers need 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 openings close, the photosynthesis rate goes down. Heat and moisture stress can cause the stomata to close.
"This can happen to the degree that the plant will run backward; it burns up its energy inside," she says. "This happens to beans if we have a hot environment and the beans can’t cool down in the evenings before the sun goes down."
CO2 levels in the canopy can influence soybean yields. Factors including row spacing, plant population and plant height could change CO2 levels in the canopy.
Moisture availability throughout the reproductive stages is critical. Bauer adds, "Soybeans need to have adequate soil moisture until the R7 growth stage. Therefore, your final irrigation should be around R6.5, depending on your soil moisture levels."
Bauer notes that addressing yield components can be an overwhelming process to begin. "Ask yourself whether there is any decision you consistently make or don’t make in the course of the season that you know hurts your yield potential—something that would be easy for you to change." She encourages, "Improve those one or two practices this year, and you’ll be on your way to higher yields."
- Early Spring 2014