In-Field Application Uniformity Evaluation of Pressure-Compensating Subsurface-Drip Irrigation Products

In the southeast United States, Subsurface Drip Irrigation (SDI) is an available agricultural irrigation practice. Research performed at the Tennessee Valley Research and Extension Center (TVREC), Belle Mina, Alabama indicated poor irrigation uniformity in an active experimental plot equipped with pressure-compensated SDI. The need therefore existed to quantify the performance of the SDI without disrupting ongoing crop research. A study was conducted to develop and validate an in-situ testing technique to assess the application uniformity of SDI, and to evaluate if variable operating pressure or slope was a significant response variable. Laboratory investigations indicated that new pressure-compensated SDI dripline of the type used at TVREC had an emitter discharge of 1.04 L h-1 (0.275 gal h-1) at 5% coefficient of variation (CV) above the manufacturer's specification of 0.98 L h-1 (0.26 gal h-1) at 2.5% CV. A trailer mounted field testing apparatus was fabricated to interface with the in-situ SDI dripline in order to deliver water over a range of operating pressures while measuring sample discharge from a predetermined number of emitters. This apparatus was tested under laboratory conditions to compare emitter discharge equivalent values with per-emitter discharge; measurements from the apparatus agreed to within a half percent of per-emitter discharge values. Field evaluations indicated that the lowest discharge occurred for the irrigated SDI dripline operating at 48-kPa (7-psi) pressure. Discharges from non-irrigated and irrigated driplines operating at 83 and 117 kPa (12 and 17 psi) were not significantly different (α= 0.05). Emitter discharge estimates were within +/-5% of the baseline discharge rate determined from laboratory evaluations (1.04 L h-1 ; 0.275 gal h-1) regardless of operating pressure or system activity, except for irrigated driplines operating at 48 kpa (7 psi) (-7%). Three sample driplines exhibited flows exceeding +/-5% of the baseline discharge; flows that may prompt a system manager to investigate this discharge anomaly more closely. Spatial yield estimates indicated that cotton lint yield may have been adversely affected by poor SDI uniformity. Techniques and equipment developed in this study provide SDI researchers and users a field method to evaluate in-situ SDI application uniformity and emitter discharge performance.