Submitted to: Frontiers in Environmental Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2025
Publication Date: 5/23/2025
Citation: Mane, S., Singh, G., Das, N., Kanungo, A., Cosh, M.H., Dong, Y. 2025. Development of low-cost handheld soil moisture measurement device for farmers and citizen scientists. Frontiers in Environmental Science. 13. https://doi.org/10.3389/fenvs.2025.1590662.
DOI: https://doi.org/10.3389/fenvs.2025.1590662

Interpretive Summary: Soil moisture monitoring can be time consuming and expensive. These aspects make soil moisture monitoring difficult to implement in citizen science protocols. A low cost and simple to operate sensor needs to be developed for citizen science and more wide spread monitoring. A new sensor was developed to operate simply using common technology and data is captured via commonly available cellular technology. Comparisons to field sampling is done to verify the quality and accuracy of the sensor, demonstrating comparable accuracy to other sensors. This work is valuable to citizen science developers as well as educators.

Technical Abstract: In recent years, the emergence of advanced technologies has highlighted the key role of in-situ soil moisture measurement in various hydrological, agricultural, and ecological applications. However, the widespread adoption of such technology has encountered obstacles due to the costs and accessibility associated with existing measurement devices. This study aims to bridge a significant research gap by designing an economical and user-friendly handheld soil moisture measurement device, referred to as the Low-Cost Soil Moisture (LCSM) measurement handheld sensor device. The primary objective of this study is twofold: firstly, the development of the LCSM device, and secondly, the establishment of robust calibration coefficients (such as generalized and soil-specific) to ensure precise measurements. Calibration experiments for the LCSM sensor device were conducted across various sites, encompassing diverse soil types and land cover conditions. These sites included the agricultural research farms of Michigan State University, characterized by mineral-rich soil, as well as the SMAP Validation Experiment in 2022 (SMAPVEX 22) campaign, which primarily focused on forest organic soil. The in-situ data collected during these experiments were utilized to establish a linear regression model between gravimetric-based volumetric soil moisture and LCSM sensor voltage (initially device measures voltage). This regression analysis allowed for the determination of robust regression coefficients also referred to as LCSM sensor calibration coefficients. This study resulted in the development of calibration coefficients for the LCSM device applicable to both mineral and organic soil types, thus enabling useful applications. To assess the efficacy of the LCSM device's calibrations, a comparative analysis was conducted between LCSM outputs and corresponding gravimetric soil moisture measurements in both mineral and organic soils. For generalized calibration of the LCSM sensor in mineral soils, an overall Root Mean Square Error (RMSE) of 0.035 m³m'³ and a bias of less than 0.001 m³m'³ were observed, alongside a strong correlation coefficient (R= 0.90). Conversely, soil-specific calibration for mineral soils yielded a lower RMSE of 0.031 m3m-3 for loam soil and 0.034 m3m-3 for sandy loam soil. In the context of forest organic soil, the LCSM device exhibited a higher RMSE of 0.078 m3m-3 with a moderate correlation coefficient (R = 0.80). Furthermore, the calibrated soil moisture readings from the LCSM sensor were compared with those obtained from other commercially available and widely used handheld soil moisture sensors/devices such as the HydraProbe and ThetaProbe. This comparison demonstrated a robust agreement, with a high correlation coefficient (R > 0.90) and minimal difference. These statistical findings underscore that the LCSM sensor-based handheld device measures soil moisture comparable to those obtained from commercially available sensors. Moreover, the comparison with other sensors strengthens the credibility and reliability of the LCSM sensor for monitoring soil moisture across diverse conditions.