Calibration of the TMS-4 Datalogger to Determine the Influence of Organic Matter on Measurements of Soil Moisture Content

Samantha Yamamoto

Master's thesis

Abstract:

The TMS-4 Datalogger (TMS-4) is an emerging device that can be used to record important climate data relevant to ecosystems and agriculture, such as temperature and Soil Water Content (SWC). However, the sensor’s performance when measuring SWC can be influenced by the presence of Soil Organic Matter (SOM), present in Compost-Amended Soil (CAS), potentially needing calibration to accommodate this influence. Thus the study aimed to calibrate the TMS-4 sensor under controlled laboratory conditions in soils from four different localities (Blatnice u Jaroměřic – loam; Jevíčko – silty clay loam; Velké Hostěrádky – silty clay loam; Uhříněves – silt loam) with consideration of compost treatment of the soil. The method of homogenised soil column was conducted with the calibration tanks of volume 24 L, able to accommodate 4 TMS-4 dataloggers at once. Eight targeted VWC were used for the calibrations: 0, 5, 10, 15, 20, 25, 30, and 35 %. Sensor outputs of SWC were compared to direct measurements of SWC from undisturbed soil samples’ gravimetric analysis either for control soil (CON), which was not amended by compost, and CAS, for each targeted VWC. Linear, Polynomial, and Logarithmic equations were derived for each calibration tank. Derived calibration equations differed from Factory Calibration (FC), with FC using Polynomial equations. While results differed between experimental localities and individual sensors, TMS-4 outputs were influenced by compost admixture. Although the SOM of the CON and CAS only differed by 1.5%, there was a considerable difference noted in TMS-4 measurements. Results between soil localities varied, and for this reason, no specific calibration equation can be recommended, however, soil-specific calibration should be considered a necessary step in research using the TMS-4. Although polynomial equations are typically used for indirect measurement calibration, the statistical fitness of polynomial equations contradicted results found with extrapolated values and directly contradicted the reality of SWC measurements for multiple localities. Logarithmic equations had lower statistical fitness but tended to be more reliable in reflecting the real behavior of measurements with changes in SWC. Linear functions had lower suitability to data owing to a change in curvature that occurred in experiments once the SWC reached Transition Water Content, a range of Water Content where the type of soil water influencing DP changes, changing DP measurements and affecting calibration. Substantial sensor-to-sensor variation was found in TMS-4 measurements, and for this reason, sensor-specific calibration is strongly recommended.

Keywords

Calibration, Time Domain Transmission, Soil Organic Matter, Soil Water Content, TMS-4 Datalogger, Dielectric Permittivity

Jazyk práce: English

Datum vytvoření / odevzdání či podání práce: 27. 4. 2024

Obhajoba závěrečné práce

• Obhajoba proběhla 23. 5. 2024
• Vedúci: Ing. Markéta Miháliková, Ph.D.
• Oponent: Jarmila Čechmánková, externi

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Master programme:
Natural Resources Management and Ecological Engineering