Soil pits as a simple design aid for subsurface drip irrigation systems

A new method for designing subsurface drip irrigation (SDI) systems, referred to as the "soil pit method", is presented in this paper. The new method involves the installation of a trial irrigation system using thin-diameter polyethylene tube emitters. Soil water flow is then monitored by observation of the wetting front (WF) on the face of a soil pit. The soil pit method was applied at two field sites located at Forbes and Warren, New South Wales, Australia. Good agreement was found between the WF observed using the soil pit method and neutron moisture meter measurements of soil water content taken at both of the field sites. Data from the soil pit method was used to derive design parameters for drip irrigation systems at both field sites. These parameters were compared to those based on soil texture. At one site (Forbes), the two methods gave similar design parameters. A comparison of emitter lateral spacings that was conducted at this site confirmed that the lateral spacing suggested by the two methods was appropriate for the site. At the other site (Warren), however, the design parameters derived from the soil pit method were considerably different from those based on soil texture, with inadequate watering and water surfacing problems experienced from the SDI system designed using soil texture. Given the simplicity of the new design method and the minimal equipment and operator expertise that it requires, the soil pit method has potential to be a valuable tool in the design of SDI systems.