Plan to adjust your irrigation throughout the season. Tensiometers and other devices are available to help you determine when to water. As mentioned previously, net irrigation is the amount of water that actually enters the soil. Gross irrigation, then, is the total amount of water pumped or sprinkled. The difference between these two numbers is the water lost due to runoff and evaporation.
Evaporative losses can be quite severe.
A typical sprinkler system operated at noon on a hot, windy, dry day in midsummer can lose 30 percent or more of the water to evaporation. The same system operated in the late evening when wind speed is low and humidity is high may only lose 15 percent of the water applied to evaporation. The most important factor for irrigation, then, is the time of application. Many are afraid to irrigate in the evening, citing increased disease problems. Irrigating at night and in the early morning will not cause increased disease problems unless the wetness period of the plant leaves is increased.