Armstrong Research and Demonstration Farm
The most common irrigation scheduling practice by Iowa vegetable growers is the imperfect soil moisture ‘feel’ method. Even during a growing season with normal rainfall,supplemental irrigation is necessary to avoid moisture stress, particularly during the blossom and fruit bulking period, which can result in lack of fruit set, reduced fruit size,sunburn fruit, and a lack of uniform ripening. The main questions are: when to turn on the irrigation system, and how long to run the pump.
Iowa State University
Taber, Henry G., "Tomato Irrigation Scheduling for Optimum Production" (2008). Iowa State Research Farm Progress Reports. 659.