Subsurface Drip Irrigation in Gravel-Filled Cavities

Subsurface drip irrigation (SDI) is regularly used to provide water and nutrients to plants while maintaining a dry soil surface. Problems associated with the practice of SDI are spatially dependent reductions in dripper discharge and possible surfacing of water resulting from positive pressure at the emitter - soil interface. These can be resolved either through prudent care in matching dripper flow rates to soil hydraulic properties or by otherwise providing conditions under which positive pressure cannot arise. We present a method where water is applied to the soil within a gravel-filled cavity. The necessary volume of gravel is determined by the contact area between the cavity and the soil and is a function of irrigation rates, dripper spacing, and soil hydraulic properties. A theoretical solution for the radius of a gravel-filled cavity based on the perimeter of the saturated zone from a line source in the soil demonstrates that larger cavities are needed as soil hydraulic conductivity decreases. The method was tested using a numeric simulation model ( HYDRUS-2D) and was used and tested in a vineyard of table grapes ( Vitis Vinifera L. cv. Sugraone) in a 7-yr study with SDI and gravel-trenched subsurface application of effluent and fertilizers.