In our soybean seed size experiment we have been monitoring soil temperatures since planting on May 8th. Mean daily soil temperatures have ranged from 52 to 60 degrees F over this time. Preliminary research suggests that soybean requires ~145 (air) and ~165 (soil) GDD's base 50 degree F for emergence. The large difference between these two measurements is related to the temperature swing difference between air and soil temperatures in the spring. We have accumulated ~80 GDD based on soil temps since planting. This experiment is planted at Arlington WI on worked ground.