Planting into wet soil may result in excessive soil compaction and the crop may suffer from restricted root development throughout the growing season. Wet soil also may prevent closure of the furrow when planting. Closure of the furrow after dropping seed into the furrow is important to protect the seed from drying out and to have good soil-seed contact necessary for rapid emergence. However, producers have had positive experiences with ultra-early planting of soybeans in several areas of Iowa during the past few years. Soil and air temperatures were above normal for early April this year, but frequently soil temperatures are cool enough that soybean seed planted in early April would not germinate for 3 or 4 weeks.
Warmer temperatures result in earlier germination of ultra-early planted seed.
Early emergence places the young seedlings in danger of damage or death from an April frost. Disease pathogens also may damage the seed and seedlings planted into cool soils. Therefore, treatment with a seed fungicide is recommended with early planting. Studies have shown that the best soybean yield results usually occur when soybeans are planted between late April and mid-May. Planting after mid-May often results in decreasing yields as shown in the figure.