One of the major factors affecting corn production in the southeastern Coastal Plain region is available soil water. Even though this region enjoys average rainfall amounts of about 50 inches per year, the amount and distribution of rainfall is highly unpredictable, making rainfed corn production risky with large variations in yield from one year to the next.
Production is further challenged by the prevailing sandy soils with low water holding capacities of 0.5 to 1.0 inch per foot overlying a difficult-to-manage hard pan that restricts root penetration into the more clayey soils below. This limits the root zone depth and thus the effective soil water storage volume.
Because of the high evaporative demand during mid-summer, available soil water is quickly depleted in sandy soils and lack of rainfall can result in yield reductions due to water stress. This was evident in the 2008 drought in South Carolina, as rainfed corn yields were miserable.
During peak water use (i.e., mid June to Mid July that includes the critical silking to milk stage), corn needs about two inches of water per week (0.3 in per day), but the probability of receiving two inches of rainfall in one week in mid season is only 20%. During this peak water use, yield loss due to water stress is substantial and estimated at 6-8% per day of stress.
It is thus obvious that corn producers must supplement rainfall with irrigation to meet full crop water needs for high yield. Although supplemental irrigation minimizes crop water stress due to inadequate and/or untimely rainfall during the season, it is costly and energy intensive and thus must be managed most efficiently to be profitable.