Noninvasive monitoring of soil static characteristics and dynamic states: a case study highlighting vegetation effects on agricultural land

This paper presents the results of seasonal monitoring and irrigation tests in a semiarid region of Sardinia, using mainly electromagnetic induction and electrical resistivity tomography time lapse monitoring. The vegetation has a significant impact on the soil moisture dynamics, changing infiltration and evapotranspiration patterns. In this paper we present the results of seasonal monitoring and irrigation tests performed on an experimental farm in a semiarid region of Southern Sardinia. The goal of the study is to understand the soil–vegetation interactions and how they can affect the soil water balance, particularly in view of possible climatic changes. We used long-term electromagnetic induction (EMI) time lapse monitoring and short-term irrigation experiments monitored using electrical resistivity tomography (ERT) and EMI, supported by time domain reflectometry (TDR) soil moisture measurements. Mapping of natural γ-ray emission, texture analysis, and laboratory calibration of an electrical constitutive relationship on soil samples complete the dataset. We observe that the growth of vegetation, with the associated below-ground allocation of biomass, has a significant impact on the soil moisture dynamics. It is well known that vegetation extracts a large amount of water from the soil particularly during summer, but it also reduces evaporation by shadowing the soil surface. Vegetation represents a screen for rainfall and prevents light rainfall infiltration but enhances the wetting process by facilitating the infiltration and the ground water recharge. In many cases, the vegetation creates a positive feedback system. In our study, these mechanisms are well highlighted by the use of noninvasive techniques that provide data at the scale and resolution necessary to understand the hydrological processes of the topsoil, also in their lateral and depth spatial variability. Unlike remote sensing techniques, noninvasive geophysics penetrates the soil subsurface and can effectively image moisture content in the root zone. We also developed a simple conceptual model capable of representing the vegetation–soil interaction with a simple enough parameterization that can be fulfilled by measurements of a noninvasive nature, available at a large scale and evidences possible relevant developments of our research.