Greg Roth
Professor of Agronomy
Warm weather will promote soybean growth and improve their color.
Soybeans normally go through an ugly stage during V2 to V3 when they are yellow and pale as the plants are growing with limited N fixation. Then it warms up and they turn dark green and grow rapidly. Lots of beans around the state seem to be in an extended stage of paleness and growers and advisors are anxiously waiting for the green phase to set in. I anticipate that with this week’s hot summer-like weather, soybeans will start into that green phase quickly, canopy over and start looking good again. I would not recommend adding any N or other nutrients at this point unless you could document a nutrient deficiency.
I have been getting reports of non-nodulated soybeans in virgin fields again from around the state, so take time now to check these fields. I have been monitoring one local field which seems to be doing well and has some nodulation. But even in this field, it seems that there are individual plants that are not well nodulated. Soybeans should have about 8 nodules by the V4 stage that are actively fixing N, with a red or pinkish interior. I have also observed on some non-nodulated fields that the green plants have a few large nodules, so they are green, but likely not nodulated up to their potential. Our standard recommendation is apply 60-70 pounds of dry N fertilizer near R1 to give these fields a boost. It would be interesting to leave a check strip in some of these fields to document the response for future reference.
Soybean yield potential is really a function of pod number, seeds per pod, and seed size. All of these have yet to be determined. Tall soybeans are not really associated with high yields, and height can be detrimental if the dense canopy leads to disease or lodging problems. One producer told me about his tall 40 bushel beans as being the nicest looking field in the county in August, only to be disappointed in the end. So I think our soybean yield potential has not been compromised yet with the delayed development.
I would continue to scout soybeans for disease and other issues in the coming weeks. Brown spot has been fairly prevalent in many fields but often does not develop into a treatable problem. White mold could become an issue if the wet weather continues. Herbicide injury that follows spray track patterns and nutrient deficiencies like potash are other issues to look for this time of year.
Source : psu.edu