Cotton has a low tolerance for wet soil conditions. The primary reason cotton is generally planted on an elevated bed is to facilitate drainage of water away from the seed zone. Other reasons include the fact that elevated beds tend to warm up quicker in the spring. As moisture drains from soil pore space it is replaced with air. The specific heat of air and water is different.
Air warms up quicker than water.
Also, as the soil dries, beds tend to hold moisture a little longer and a grower may drag the bed flat to reach enough moisture to get a stand. As this happens it is acceptable to plant cotton flat. In fact, a lot of fields will drain better flat than when the field is bedded. If a field had not been formed, or placed on some type grade, bedding may cause water to be caught in low areas of the field. This operation should be carried out immediately after the field is bedded and again after planted.