Abstract
Electromagnetic induction (EMI) technique is an established method to measure the apparent electrical conductivity (ECa) of soil as a proxy for its physicochemical properties. Multi-frequency (MF) and multi-coil (MC) are the two types of commercially available EMI sensors. Although the working principles are similar, their theoretical and effective depth of investigation and their resolution capacity can vary. Given the recent emphasis on non-invasive mapping of soil properties, the selection of the most appropriate instrument is critical to support robust relationships between ECa and the targeted properties. In this study, we compared the performance of MC and MF sensors by their ability to define relationships between ECa (i.e., MF–ECa and MC–ECa) and shallow soil properties. Field experiments were conducted under wet and dry conditions on a silage-corn field in western Newfoundland, Canada. Relationships between temporally stable properties, such as texture and bulk density, and temporally variable properties, such as soil water content (SWC), cation exchange capacity (CEC) and pore water electrical conductivity (ECw) were investigated. Results revealed significant (p < 0.05) positive correlations of ECa to silt content, SWC and CEC for both sensors under dry conditions, higher correlated for MC–ECa. Under wet conditions, correlation of MF–ECa to temporally variable properties decreased, particularly to SWC, while the correlations to sand and silt increased. We concluded that the MF sensor is more sensitive to changes in SWC which influenced its ability to map temporally variable properties. The performance of the MC sensor was less affected by variable weather conditions, providing overall stronger correlations to both, temporally stable or variable soil properties for the tested Podzol and hence the more suitable sensor toward various precision agricultural practices.
Highlights
Characterization of spatiotemporal variability of relevant physicochemical properties of soil is crucial for precision agriculture and for various environmental sectors [1]
The results further suggested a higher susceptibility of the MF–electrical conductivity (ECa) to soil water content (SWC) variation, which could limit its operation for SWC mapping
We performed a comparative study using MF and MC electromagnetic induction (EMI) sensors to assess their ability for mapping properties for shallow soils under dry and wet conditions as relevant for agricultural purposes
Summary
Characterization of spatiotemporal variability of relevant physicochemical properties of soil is crucial for precision agriculture and for various environmental sectors [1]. Soil sampling and laboratory analyses are carried out to understand the spatiotemporal variability of soil properties. Conventional methods involve invasive soil sampling which is expensive and time consuming and only provide point information. Soil sampling is often technically not feasible for large-scale and extended temporal monitoring or for areas with restricted accessibility [2,3,4,5]. Sensors 2020, 20, 2330 allows for an indirect, cost effective, and non-invasive mapping of relevant soil properties over larger areas (e.g., 30 ha [6,7]). Non-invasive in situ techniques may allow a reduction in the excessive use of environmentally unfriendly chemical-based laboratory analyses
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