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

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–vegeta on interac ons and how they can aff ect the soil water bal-ance, par cularly in view of possible clima c changes. We used long-term electromagne c induc on (EMI) me lapse monitoring and short-term irriga on experiments monitored using electrical resis vity tomography (ERT) and EMI, supported by me domain refl ec-tometry (TDR) soil moisture measurements. Mapping of natural γ-ray emission, texture analysis, and laboratory calibra on of an electrical cons tu ve rela onship on soil sam-ples complete the dataset. We observe that the growth of vegeta on, with the associated below-ground alloca on of biomass, has a signifi cant impact on the soil moisture dynamics. It is well known that vegeta on extracts a large amount of water from the soil par cularly during summer, but it also reduces evapora on by shadowing the soil surface. Vegeta on represents a screen for rainfall and prevents light rainfall infi ltra on but enhances the wet-ng process by facilita ng the infi ltra on and the ground water recharge. In many cases, the vegeta on creates a posi ve feedback system. In our study, these mechanisms are well highlighted by the use of noninvasive techniques that provide data at the scale and resolu-on necessary to understand the hydrological processes of the topsoil, also in their lateral and depth spa al variability. Unlike remote sensing techniques, noninvasive geophysics penetrates the soil subsurface and can eff ec vely image moisture content in the root zone. We also developed a simple conceptual model capable of represen ng the vegeta on–soil interac on with a simple enough parameteriza on that can be fulfi lled by measurements of a noninvasive nature, available at a large scale and evidences possible relevant develop-ments of our research. Abbrevia ons: EMI, electromagne c induc on; ERT, electrical resis vity tomography; TDR, me do-main refl ectometry. Upscaling knowledge on soil moisture dynamics and vegetation growth into the soil from the small scale of a single root and soil structure (see e.g., Javaux et al., 2008) to the larger fi eld scale is still a partially unexplored and challenging task that has relevant implication in the interdisciplinary fi elds of ecohydrology and geoecohydrology. Th e form of root growth is an important aspect of the study of vegetation in arid areas, but the plant root system is not easily accessible and far less studied. Th e structure and function of roots are expected to evolve for optimal uptake of water leading eventually to competition among diff erent species (Cody, 1986 and reference therein). In terms of coupled dynamics, the soil supports the plant growth and, conversely, the below-ground architecture of plants can aff ect the soil structure and thus its physical char-acteristics having an indirect impact on the subsurface water fl uxes. Soil moisture balance and biomass balance are strongly interconnected due to their two-way interaction and the positive and negative feedbacks that take place between the dynamics of water and the vegetation growth.

Cassiani, G.; Ursino, N.; Deiana, R.; Vignoli, G.; Boaga, J.; Rossi, M.; Perri, P.; Blaschek, M.; Duttmann, R.; Meyer, S.; Soddu, A.; Dietrich, P.; Werban, U.; Ludwig, R. 2012. Noninvasive monitoring of soil static characteristics and dynamic states: A case study highlighting vegetation effects on agricultural land. Vadose Zone Journal, 11(3).