Application of additional irrigation water increased hay yields, but water in excess of about 2 feet did not appear to be particularly beneficial, according to recent tests at Davis. Adding the depth of initial soil moisture storage, and assuming an irrigation efficiency of 70%, the total annual water requirement of alfalfa under these conditions is about 4 1/2 acre-feet. When water supplies are deficient, a good crop can be maintained with less than 8 inches of water applied, if the soil moisture reservoir is full in the spring. If about 2 feet of water is available for the hay crop, there appears to be little difference between applying water early or in equal amounts throughout the season.