Comparison test on drip irrigation tape hydraulic performance under low-pressure between subsurface drip system and surface drip system

Abstract: With the wide spread of drip irrigation, low-pressure subsurface drip system has come into notice as it can reduce the operation cost and improve water and fertilizer use efficiency, and it has become an emerging trend in drip technology development. A field experiment was carried out in Xinjiang to investigate the variation law of hydraulic performance and irrigation uniformity in subsurface drip system under low pressure. We chose lateral capillary from the head and end of the main branch to be the representatives, as well as the middle ones. The inlet pressure of branch pipe was set between 1.40 and 6.55 m; then we compared subsurface drip system with surface drip system under the same conditions in relation to flow rate, working pressure, and total head loss. The results indicate that: 1) The operation status of laterals can be monitored by working pressure and flow rate in the drip irrigation system. 2) When the emitter outflow is driven by the soil matric potential, the flowrate of underground laterals is larger than that of the surface laterals, and the coefficient of flow variation is increasing by 0.12 to 0.9, and it keeps increasing with the decrease of working pressure. 3) When comparing the working pressure of subsurface drip system with that of the surface drip system, 90% of subsurface drip laterals are less than that in the surface drip irrigation system, and the variation coefficient of working pressure is from ?10% to 0 with the probability of 70%. 4) The increasing coefficient considering local head loss of laterals (ICCLHLL) is calculated by using the total head loss, the Blasius formula, and the flow from multiple outlets, and the value of surface drip system is within the range of 1.32-5.94, while range between 1.37 and 2.18 for subsurface drip system, and the ICCLHLL increases with the decrease of working pressure. The flow rate of subsurface laterals keeps increasing under the influence of the soil matric potential, which leads to the decrease of ICCLHLL in surface drip laterals. 5) When decreasing working pressure, the irrigation uniformity of surface drip system will also decline. The soil matrix potential improves the irrigation uniformity of subsurface drip system. The deviation rates of working pressure and flow rate in the subsurface drip system are 0.62%-3.44% and 8.15%-22.4% lower than those in the surface drip system, respectively. The research can provide a scientific basis for design and management of low-pressure subsurface drip irrigation.