Regarding yield potential of early-planted soybeans, I've been asked about slow emergence and environmental stress. One point brought up repeatedly is that because seed had lain in the ground for an extended period of time, they are not as vigorous and are more susceptible to disease.
Soybean seed planted into cool soils are usually just as good as seed in the sack. Three things make this so: (1) adequate drainage; (2) use of a proper seed treatment, and (3) high-quality seed. Over the years I have seen seed remain viable and produce excellent yields when emergence took from 12 to 14 days and in several situations when emergence occurred over 20 to 30 days.
The time to emerge when seed are planted early is based on cool temperatures, moisture availability and depth of planting.
Seed placed in cold soils will lie there and wait for temperatures to warm. The germination process will begin at 55 degrees Fahrenheit. At 65 F, emergence will take place in approximately a week. If temperatures yo-yo up and down, the process will be slowed.
Does taking two weeks to emerge affect vigor of the seeding? No.
Seed that took two weeks or longer to emerge this spring did so because it was too cold or there was not adequate moisture or a combination of the two. I never thought we would go several weeks without rain in early April. If you planted into dry soil, the seed had to lie there until they received adequate moisture. If you were in the north Delta and got the big rains, seed did not start the germination process until some oxygen became available in the soil. Once it started drying, germination began.
Planting depth will also affect speed of emergence. This is one reason I suggest planting shallow when planting early. Because soil warms faster at shallower depths, emergence will occur faster and probably be more uniform.
Another reason to plant shallow is to keep seedlings from struggling to emerge after a hard packing rain. Rainfall frequency and intensity are much greater early than late, and shallow planting early will help minimize replanting.
Replanting may be necessary for those who planted deep. I refuse to chase moisture when planting early. A dry late March/early April is not the norm.
I have been told that because emergence is delayed, young seedlings are more susceptible to seedling disease. This could happen, but where a good broad-spectrum seed treatment is used in conjunction with high-quality seed we have not found this to be true (we have observed slow emergence due to pre-emergence herbicides).
A big rain at cracking where pre materials have been applied does cause slow growth of seedlings, potentially increasing the plants' susceptibility to pythium. To avoid this, apply any pre-emergence materials early enough to get a rain prior to emergence, essentially eliminating any herbicide injury problems.
Many farmers have expressed concern regarding slow emergence. This has not affected seedling vigor. Slow emergence when it is cool does not compare to seed lying in dry soil in June when it is hot.
Others questions concern seedlings in the crook stage that turned black during recent cool nights. Some farmers were told the young seedlings would not emerge and were dying, and that they should replant. I asked, “Was the neck black or dark purple?” Upon closer inspection everyone told me they were purple.
Purple color on the hypocotyl (stem) means the plants are going to have a purple bloom. If the stems are green, the plants will have white blooms. One farmer was told to apply phosphorus because the plants stem were purple. He may need to apply phosphorus, but he should not base that decision on stem coloration.
I compliment everyone who is looking at this crop closely. I am proud of those asking questions. But before you believe everything you hear, ask someone who might have an idea, not someone who is speculating. Speculation has fueled a lot of uncertainty so far this season. Slow emergence alone is no cause for alarm. I have spent a lot of time over the past few weeks looking at fields. I have seen some pythium even on treated seed and thin stands due to improper seed placement, but I have seen no problem due to cool conditions.
Alan Blaine is the Mississippi Extension soybean specialist. e-mail: firstname.lastname@example.org.