Two experiments were conducted in the Imperial Valley of Southern California to study the effects of irrigation management on alfalfa yield, stand persistence, and soil salinity levels in the root zone.

Irrigation treatments were based on frequency as determined by tensiometers and on duration of irrigation. Soil in Experiment I was mainly clay and clay loam to 3 m. Soil in Experiment II was clay loam, silty clay loam, and clay in the top 1½ m and sandy clay loam and sandy loam in the next 1½ m of depth. Rainfall was negligible.

Frequent short irrigation (FS) or moderate treatment was superior in yield, stand persistence, and hay quality in Experiment I. Phytophthora root rot was found in the frequent long (FL) or wet treatment. In Experiment II yield was similar for all treatments, but an invasion of grass resulting from weaker stands reduced the quality of the hay produced in the FL treatment. Disease incidence was low in the normal short (NS) or dry treatment but relatively high in the other two treatments.

Use of tensiometers at the 30- and 61-cm depth demonstrated the possible use of tensiometers in alfalfa forage production and some of the problems encountered in irrigation.

Soil salinity was inversely related to hours of applied irrigation in both experiments for the 20-45 cm and 45-70 cm depths and for practically all sampling dates during the second year.

In leaching treatments superimposed on Experiment I at the end of the experiment, EC values increased slightly with three 3-hour irrigations. Thirteen irrigations with 24- and 3-hour durations resulted in consistent but similar reductions in soil salinity.