Deficit Drip Irrigation Impacts On Growth and Fruit Retention of Pima Cotton

Modern commercial Pima cotton varieties in California typically require a longer growing season, more total fruiting branches, and more retained fruit per branch to achieve lint yields similar to Acala cotton grown under the same conditions.  Pima and Acala cotton were grown in a clay loam soil during two seasons using subsurface drip irrigation in treatments that produced a minimum of five irrigation treatments.  These irrigation treatments represented different levels of deficit irrigation (as a percent of evapotranspiration estimate) applied at different growth stages starting in the period about two weeks prior to first bloom through after cutout.  This irrigation management approach resulted in plants that were exposed to different intensities of water stress and different timing for the onset of significant plant water stress.   Impact of water deficit treatments on measures of plant growth (height, internode distances, average leaf size at specific node or branch locations) and fruit retention and size were determined at intervals.  One growing season during the two years of this experiment represented a low fruit retention year due to extreme Lygus pressure, while the other was a more normal, mild to moderate Lygus bug year, resulting in higher fruit retention across most irrigation treatments.  Presented information will include a limited number of comparisons with measurements made in adjacent Acala cotton plots grown under the same irrigation treatments.