Application of EMI and FDR Sensors to Assess the Fraction of Transpirable Soil Water over an Olive Grove

Abstract

Accurate soil water status measurements across spatial and temporal scales are still a challenging task, specifically at intermediate spatial (0.1-10 ha) and temporal (minutes to days) scales. Consequently, a gap in knowledge limits our understanding of the reliability of the spatial measurements and its practical applicability in agricultural water management. This paper compares the cumulative EM38 (Geonics Ltd., Mississauga, ON, Canada) response collected by placing the sensor above ground with the corresponding soil water content obtained by integrating the values measured with an FDR (frequency domain reflectometry) sensor. In two field areas, characterized by different soil clay content, two Diviner 2000 access tubes (1.2 m) were installed and used to quantify the dimensionless fraction of transpirable soil water (FTSW). After the calibration, the work proposes the combined use of the FDR and electromagnetic induction (EMI) sensors to measure and map FTSW. A strong correlation (R 2 = 0.86) between FTSW and EM38 bulk electrical conductivity was found. As a result, field changes of FTSW are due to the variability of soil water content and soil texture. As with the data acquired in the field, more structured patterns occurred after a wetting event, indicating the presence of subsurface flow or root water uptake paths. After assessing the relationship between the soil and crop water status, the FTSW domain includes a critical value, estimated around 0.38, below which a strong reduction of relative transpiration can be recognized.

Soil Water Conservation: Dynamics and Impact

“…The methodology proposed by Rallo et al [23] appears usable to monitor the variations in soil water content in response to irrigation and root water uptake. Moreover, it has the practical potential to be flexible in terms of spatial and temporal sampling resolution.…”

“…Finally, Akramkhanov et al [28] involved local stakeholders in Uzbekistan in a transdisciplinary and participatory approach for innovation development. From a methodological point of view, the contributions involve both field [15,16,18,23,24,29] and laboratory [19] experiments, and modeling [20][21][22], survey [17,27,28] and review [25] studies. The Special Issue includes studies carried out at different spatial scales, from field-to regional-scales.…”

“…The Special Issue includes studies carried out at different spatial scales, from field-to regional-scales. A wide range of geographic regions are also covered, including Brazil [16], Mediterranean basin [15,23,24,26,29], central Europe [18], China [20][21][22], Sub-Saharan Africa [17,25,27], and central Asia [28].…”

“…Two other papers focus on novel monitoring [23] and experimental [24] approaches for soil hydraulic characterization. With the aim of measuring and mapping the fraction of transpirable soil water, Rallo et al [23] compared the cumulative EM38 (Geonics Ltd., Mississauga, ON, Canada) response collected by placing the sensor above ground with the corresponding soil water content obtained by integrating the values measured with a frequency domain reflectometry sensor.…”

“…The aim of this Special Issue is to enhance our understanding on conservation strategies for effective and sustainable soil and water management. Contributions focus on: recovery of soil hydraulic properties [14][15][16]; erosion risk [17][18][19]; novel modeling [20][21][22], monitoring [23] and experimental [24] approaches for soil hydraulic characterization; improvement of crop yields [25,26]; water availability and food security [27]; and soil salinity [28]. In the following section we resume all the contributions of this Special Issue.…”