SUBSURFACE DRIP AND FURROW IRRIGATION COMPARISON WITH ALFALFA IN THE IMPERIAL VALLEY

A subsurface drip irrigation (SDI) and furrow irrigation study was installed in a silty clay loam soil at the USDA-ARS Irrigated Desert Research Station near Brawley, CA in early 1991 to evaluate the potential for water savings and yield improvements with subsurface drip irrigation of forage alfalfa as compared to furrow irrigation. In bed-planted alfalfa, subsurface drip lateral spacings of 1.02 m (40 inch) and 2.04 m (80 inch) installed at an average depth of 40 cm below bed centers were investigated beginning in 1991. During the first one and one-half year operation, approximately 20 percent higher yields were achieved in the drip plots with 94 percent of the water application amounts used in the furrow irrigated plots. Problems with surface soil wetting were noted in all drip treatments during the 1991-1992 phase (Phase I) of the experiment. These problems resulted in the decision to reduce water applications during a "dry-down " period during each harvest cycle to allow for harvest equipment traffic while limiting potential for soil compaction and plant damage from equipment. To provide an alternative method to deal with the surface soil wetting, the alfalfa crop was terminated in late 1992, the drip system replaced at 63 to 70 cm (25 to 28 inch) depth, alfalfa replanted in 1993, and the system operated in subsequent years. During this second phase (Phase II), applied water and evapotranspiration were similar (within 5 percent) in drip and furrow irrigated plots, while yields averaged between 19 and 35 percent higher in subsurface drip irrigated plots during the 1993 through 1996 period. Problems with surface soil wet areas were nearly eliminated with the deeper drip lateral placement during the 1993 through 1996 period. Additional work was conducted to determine long-term impacts of long-term drip system operation on patterns of salt accumulation using Colorado River water