Mapping Spatial Patterns of Water and Solutes Under Drip Irrigation Using Electrical Resistivity Tomography and Water Flow – Solute Transport Model.

Mapping and understanding the spatial patterns of water and salt distribution and especially under limiting water resources, are of high importance both for irrigation control and the understanding of root uptake processes. However, in most cases these patterns are either assumed based on homogeneity assumption, or estimated using several (typically one at most) in-situ sensors. In this research we employ electrical resistivity tomography, a geophysical non-invasive and non-destructive technique, to map the spatial and temporal patters of water in the root zone of orchards reflecting variety of soil and climate zones along the coastal plain of Israel.

In most sites the resistivity mapping reviled patterns resembling the classic ‘onion’ shape, but in some cases biased from the classic shape mostly with respect to the existence of layering (in cases such not known to the farmer).  However, examination of the temporal patterns indicated that these patterns are not necessarily the outcome of water flow but also of solute dynamics. To separate the water and salt signature we developed a simple flow and transport model considering electrical conductivity as the modeled ‘solute’. This allowed us to better understand the water and salt dynamics of the orchards. We conclude that in wet regions resistivity can be used as a tool for mapping, even at temporal resolution close to real-time, the water flow dynamics, but in arid region more care should be given to salt dynamics which somewhat complicates the application. Such understanding of water and salt dynamics allows for more efficient irrigation control, understanding of temporal and spatial root uptake patterns, and high resolution evaluation of aquifer recharge as well of salt and agrochemical leaching.