Plant species exhibit different types of emergence . In some crops, the cotyledons remain in the soil as either the mesocotyl or epicotyl elongates and pushes to the surface. In others, the hypocotyl elongates pulling the cotyledons to the soil surface. When comparing crops with similar seed size, those that must pull their cotyledons through the soil for emergence should be planted shallower than those in which the cotyledons remain in the soil. Depth of planting is also influenced by soil type.
Deeper plantings are possible in lighter soils than in heavy soils .
The surface dries out quickly in sandy soils making deeper plantings necessary for placing the seed in moist soil. In cold, wet soils, shallower plantings are required because the oxygen concentration and temperature at greater depths may be too low for germination, especially in early spring. These three crops were chosen because of the different types of emergence they exhibit. Corn is a monocotyledon in which the mesocotyl elongates during germination and the cotyledon, which serves as the food reserve for the germinating seed, remains below the soil surface during germination. Beans are dicotyledons that pull their cotyledons above the soil surface due to elongation of the hypocotyl.