By Dr. Harold Willis
An ideal seedbed for soybeans should provide adequate moisture and warmth for rapid germination and seedling establishment. Soil should be friable and not crusted. Germination of weed seeds should be delayed or prevented.
Soybeans need a lot of moisture to germinate (50% of their weight). Soil moisture must be sufficient at planting depth. There should be good soil-seed contact. If soybeans get off to a rapid start, young weeds can be shaded out. One way to discourage weeds is to prepare an ideal seedbed only in the rows and leave the soil rough and cloddy or covered by residue between the rows. Another approach is to prepare the seedbed well ahead of planting, let the weeds germinate, then re-till just before planting to kill sprouted weeds.
Most people use herbicides to control weeds, but such chemicals may have their deleterious environmental effects, and their use can be avoided.
As mentioned earlier, use good quality seed of high germination rate (80 to 90% or more). If soybeans have not been grown on that soil for three to five years, it is best to inoculate the seed with the proper strain of nitrogen-fixing bacteria (Rhizobium). Some strains are more effective nitrogen fixers than others. The bacterial inoculant can be applied to the seed just before planting time or in the row during planting (the latter requires more inoculant).
Seed can also be treated with fungicide, but unless the soil is cold, if the germination rate is over 85%, there is little advantage in this. Lower germination seed may have a 5 to 10% increase in emergence if treated.
Early planting usually gives higher yields, but only if a good stand is obtained. Cool weather will delay germination and allow root diseases or pests to get a start. Soil and air temperatures of 55 to 60 degrees F. are needed for good germination and seedling establishment. Germination rates increase at warmer temperatures, and high quality seed is more likely to produce a good stand. The predicted weather is probably the most important factor to consider, along with your local soil conditions. Adequate moisture is essential for germination.
Source: How to Grow Super Soybeans