Germination is time after the seed is planted in the soil and before the young seedling emerges above the soil surface. After being planted in the soil, the seed absorbs moisture (called imbibition), changing from less than 13% moisture to about 50% in several hours. After one or two days the first root (called the radical) emerges through the seed coat and begins growing downward to establish the root system.
About five to ten days after planting, the new seedling arches through the soil surface (this is called emergence). The hypocotyl ‘hook’ (the emerging portion just below the cotyledons) begins to lengthen pulling the remainder of the seed upward, and the oval seed leaves (called cotyledons) open up. The cotyledons provide the seedling with a temporary source of food (plant useable nutrients originally stored as the seed was formed). The cotyledons quickly turn green and begin making additional food by photosynthesis. Shortly after the first set of true photosynthetic leaves is formed, the cotyledons drop off.
Seed germination and emergence is a critical period in the life of a soybean because poor emergence due to low temperatures, a soil crust, or seed planted too deeply allows seedling pests or diseases to drastically reduce yield.