Hydrogeophysical soil study at a drip-irrigated orchard, Portugal

摘要

Non invasion techniques of electrical resistivity and radar combined with soil hydrology methods of dye tracer, time domain reflectometry (TDR) and tensiometer are applied to a drip-irrigated peach orchard of Atalaia near Lisbon, Portugal. Four experiments were carried out in the summer of 1998: a single driplet irrigation with applying dye tracer, a daily drip irrigation, a drip irrigation after 9 days of dryness (water stress) and ponding infiltration of dye tracer. The former 3 irrigation experiments were found inside tree pots and the latter ponding one outside root zones. The study is directed towards temporal and spatial mapping of soil moisture distribution in root zones under drip irrigation and under ponding infiltration in the sandy soil, where a certain patchiness in moisture distribution is expected. The structure and morphology of flow processes is monitored under infiltrating driplets and between irrigation cycles (5 h per day). The applied integrative interpretation technique of trial-and-error 3D resistivity inversion using forward modelling is generally capable of mapping the subsurface and distinguishing the root and moisture distributions from each other in a more realistic manner. Strong non-uniform preferential flow paths are modelled and observed under infiltration of dye tracer which may be similar to natural ponding. The paths become finer and more complex with increasing depth. The reliability of the resulting model is supported by the subsurface excavation and photographic imaging of the dye tracer technique.