Calculation of soil water content using dielectric-permittivity-based sensors – benefits of soil-specific calibration

[摘要] Soil water content (SWC) sensors are widely used forscientific studies or for the management of agricultural practices. The mostcommon sensing techniques provide an estimate of volumetric soil watercontent based on sensing of dielectric permittivity. These techniquesinclude frequency domain reflectometry (FDR), time domain reflectometry(TDR), capacitance and even remote-sensing techniques such asground-penetrating radar (GPR) and microwave-based techniques. Here, we willfocus on frequency domain reflectometry (FDR) sensors and more specificallyon the questioning of their factory calibration, which does not take intoaccount soil-specific features and therefore possibly leads to inconsistentSWC estimates. We conducted the present study in the southwest of Franceon two plots that are part of the ICOS ERIC network (Integrated CarbonObservation System, European Research and Infrastructure Consortium), FR-Lamand FR-Aur. We propose a simple protocol for soil-specific calibration,particularly suitable for clayey soil, to improve the accuracy of SWCdetermination when using commercial FDR sensors. We compared the sensingaccuracy after soil-specific calibration versus factory calibration. Ourresults stress the necessity of performing a thorough soil-specificcalibration for very clayey soils. Hence, locally, we found that factorycalibration results in a strong overestimation of the actual soil watercontent. Indeed, we report relative errors as large as + 115 % with afactory-calibrated sensor based on the real part of dielectric permittivityand up to +  245 % with a factory-calibrated sensor based on the modulusof dielectric permittivity.

[学科分类] 再生能源与代替技术