Deficit Irrigation Under SDI Versus Furrow Irrigation in the San Joaquin Valley: Pima and Upland Responses

Two separate multi-year studies were conducted to evaluate crop responses to deficit irrigation management approaches under subsurface drip irrigation (SDI) and furrow irrigation management in the San Joaquin Valley of California.   The studies were conducted in a clay loam soil at the University of CA West Side Research and Extension Center in western Fresno County, an area with a semi-arid, warm to hot summer climate with little or no chance of spring and summer growing season rainfall.   The deficit irrigation approach in the subsurface drip study was to apply irrigation amounts ranging from 40 to 100 percent of estimated evapotranspiration (ETc) during three different growth stages, roughly being the period prior to first bloom, from bloom through early cutout, and early cutout to irrigation termination.  In furrow irrigation treatments, deficit irrigation treatments were imposed by changing irrigation frequency and total number of irrigations applied, resulting in large differences in applied total irrigation water.  In both subsurface drip irrigation and furrow irrigated treatments, pre-plant or early season irrigation were applied that were adequate to refill the soil profile to field capacity in the upper 1.2 to 1.3 m of the profile.  Impacts of irrigation treatments on crop water stress levels, lint yields, and key fiber quality characteristics of the Upland and Pima cultivars included in the studies will be discussed.