School of Science and the Environment, Memorial University of Newfoundland, Corner Brook, NL A2H 5G4, Canada.
Sensors (Basel). 2020 Apr 19;20(8):2330. doi: 10.3390/s20082330.
Electromagnetic induction (EMI) technique is an established method to measure the apparent electrical conductivity (EC) 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 EC and the targeted properties. In this study, we compared the performance of MC and MF sensors by their ability to define relationships between EC (i.e., MF-EC and MC-EC) 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 (EC) were investigated. Results revealed significant ( < 0.05) positive correlations of EC to silt content, SWC and CEC for both sensors under dry conditions, higher correlated for MC-EC. Under wet conditions, correlation of MF-EC 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.
电磁感应（EMI）技术是一种成熟的方法，可测量土壤的视电导率（EC），以此作为其物理化学性质的代理指标。多频（MF）和多线圈（MC）是两种商业上可用的 EMI 传感器。虽然工作原理相似，但它们的理论和有效探测深度以及分辨率能力可能会有所不同。鉴于最近对土壤性质的非侵入性制图的重视，选择最合适的仪器对于支持 EC 与目标性质之间的稳健关系至关重要。在这项研究中，我们通过 MC 和 MF 传感器定义 EC（即 MF-EC 和 MC-EC）与浅层土壤性质之间关系的能力来比较它们的性能。在加拿大纽芬兰省西部的青贮玉米田进行了干湿条件下的野外实验。研究了时间稳定性质（如质地和体积密度）和时间可变性质（如土壤含水量（SWC）、阳离子交换容量（CEC）和孔隙水电导率（EC））之间的关系。结果表明，在干燥条件下，两种传感器的 EC 与粉土含量、SWC 和 CEC 均呈显著正相关（<0.05），MC-EC 的相关性更高。在潮湿条件下，MF-EC 与时间可变性质的相关性降低，特别是与 SWC 的相关性降低，而与砂和粉土的相关性增加。我们得出的结论是，MF 传感器对 SWC 的变化更敏感，这影响了其绘制时间可变性质的能力。MC 传感器的性能受多变的天气条件影响较小，为所测试的灰化土提供了与时间稳定或可变土壤性质的整体更强相关性，因此更适合各种精准农业实践。
