Lateral hydraulic performance of subsurface drip irrigation based on spatial variability of soil: experiment

Under the zero slope conditions of surface drip irrigation the emitter discharge along the lateral is also decreased for non-compensating emitters. However, in subsurface drip irrigation the lateral emitter is buried in the soil and the pressure of the emitter outlets is affected by soil physical properties. Because of the spatial variability of soil physical properties, the emitter discharge along the lateral is complex; the traditional discharge equation could not show the influence of soil properties on emitter discharge. A new emitter discharge formula is established that has soil initial water content, soil bulk density, mass fractal dimension, and head pressure as factors, and a nonlinear mathematical model of lateral hydraulics based on the emitter discharge formula is created. Experiments were then conducted to: verify the model, compare the HEPING emitter (with an inside diameter of 12 mm and outside diameter of 13 mm) and PLASSIM emitter (with an inside diameter of 14 mm and outside diameter of 15.2 mm), and assess the relative contribution of various factors to emitter discharge. The results of the experiments indicate that: ① the emitter discharge along the lateral head in the direction of flow followed a decline law in homogeneous soil, and decreased in a fluctuating manner in heterogeneous soil; ② the larger standard deviation of soil initial water content, bulk density, mass fractal dimension when each factor remained the same, the more disperse the emitter discharge along lateral.