Cotton irrigation with LEPA and subsurface drip systems on the southern High Plains
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Irrigations were delivered by LEPA and subsurface drip irrigation (SDI) systems to cotton grown in 1995, 1996, and 1997 at the Texas Agricultural Experiment Station at Halfway, TX. The LEPA treatments were irrigated on 1,2, and 3-day intervals while all SDI treatments were irrigated daily. Irrigation timing and amounts were determined from a protocol which compared calculated field water content to a target soil water content with the target water content providing a controlled decrease in soil water from peak bloom to the end of the growing season. Irrigation quantities were also restricted to maximum irrigation delivery rates of 0.1, 0.2, or 0.3 in./day. Detail profile wetting was monitored during preplant irrigations to evaluate seed germination in SDI and LEPA plots. Lint yields and water use efficiencies were significantly higher when LEPA irrigations occurred at 2-day rather than 1 or 3-day intervals within the 0.1 in./day irrigation capacity. Differences among interval treatments were smaller as irrigation capacity increased to 0.2 and 0.3 in./day. Within the 0.1, 0.2, and 0.3 in./day capacities, SDI lint yields at 1145, 1225, and 1259 lb/acre resulted in significantly higher 3-year average yields than the best LEPA treatments at 980, 1142, and 1187 lb/acre, respectively (P<0.05, Duncan). Water use efficiencies were significantly higher for SDI than LEPA treatments under the management protocol used in this experiment with differences attributed to higher soil surface evaporation of the LEPA system. SDI, with emitter spacing of 24 inches, emitter flow rate of 0.336 gal/hr at 8 psi, and depth of 12 inches in alternate furrows, successfully wetted a dry seedbed for seed germination in an Olton loam soil without rainfall.
