The drought's effect on soybeans will become a concern soon here and across the United States. If you have a good stand, the big impact will be at pod fill if we don't get timely rain. Most fields around here have decent stands but some are lacking and there is no moisture to sprout double crop soybeans. Those acres are minimal in Ohio this year and not too important unless you are the one depending on that income.
"Soybean is susceptible to yield loss from water deficit, drought stress, at two key developmental stages, germination and reproduction-seed development. Soybean must imbibe about 50 percent of its weight in water to germinate and begin to develop the radicle and hypocotyl, the primary root and shoot tissues. Seed planted into dry soil, or not placed into the soil, will be unable to imbibe water at all until adequate precipitation has occurred. Soybean can respond to water deficit as early as two days after germination. Water deficit at this time results in poor hypocotyl elongation, while root elongation may be unaffected.
Drought stress at later vegetative stages of development has similar results: shoot growth is decreased or stopped, but roots can continue to grow. This evolutionary response in soybean allows the plant to search for additional soil water while having an overall low water use rate. Assuming adequate rainfall occurs again, soybean have the ability to reinitiate shoot growth, and shoot growth rate may be greater than that observed prior to the onset of drought stress. This is called compensatory growth.
Short-term, moderate drought stress during vegetative growth stages generally does not impact soybean yield. Conversely, longer-term severe drought stress can cause irreversible plant cell death causing low growth yield.
Soybean yield is most sensitive to water deficits during reproduction. Soil water deficits during reproductive growth phase results in increased flower abortion, reduced pod number, reduced seed per pod, and small seed. Nitrogen fixation is a key biochemical pathway for soybean yield and nitrogen fixation can be severely limited or completely halted by even moderate drought stress. Once nitrogen fixation has been stopped, substantial precipitation and soil water accumulation is required to reinitiate the process. Compensatory reproductive growth rarely will occur in soybean under moderate drought stress at reproductive growth phases.
Management practices that leave low amounts of residue on the soil surface or cause compaction can reduce soil water infiltration rate. Excessive or poorly timed tillage can cause soil compaction and increase water runoff from high intensity storm events. Reduced compaction and increased water infiltration rate can increase soil water content, nitrogen fixation, and soybean yield, particularly during growing seasons with less than adequate precipitation."
Nitrogen fixation seems to be limited at this time. Soybeans are too yellow to suit me this year. They probably needed some supplemental nitrogen at planting time to get them going good. We saw one black green soybean field northeast of Paris, Illinois Saturday and I would assume the farmer knifed on anhydrous, got rained out and planted soybeans later. Everything else from Maryland to Illinois have been less green, most are accetably green but many are too yellow.
Mother Nature once again has the upper hand on soybean yields. It will take water after flowering to make an acceptable yield.
The picture shows what my beans looked like two years ago. It never rained much after the picture that year and they made a tremendous yield but we don't have anything that looks like that this year.