Multi-factor evaluation and modeling correction of EC-5 and 5TE soil moisture content sensors

Soil property information is vital to plant growth and is a fundamental eco-system resource for terrestrial vegetation, especially soil moisture content (SMC), soil electrical conductivity (EC) and near-surface soil temperature. Wireless sensor network (WSN) technology enables monitoring soil water content changes with a high spatial and temporal resolution; however, WSN specifically requests sensors with features of low-cost, energy efficiency, dependability, and ease-of-use. In this paper, after evaluating different sensors under the demand of WSN application, a pair of ECH2O sensors were chosen and tested under experiments based on a standardized sensor characterization methodology using liquid medium. The results show that the electronics of the EC-5 and the 5TE are sensitive to temperature, electric conductivity and pH variations. In terms of the 5TE, conductivity correction is more necessary than temperature and pH, and the R2 of the conductivity correction equation reaches 0.918. However, though encountering the same temperature stability as the 5TE, EC-5 exhibits an opposite characteristic when it comes to conductivity and pH correction where pH compensation plays a more essential part with a calibrated R2 of 0.978. Moreover, the inherent temperature measuring ability of 5TE is dissatisfying and the calibration with a R2 of 0.993 is well generated, but the conductivity measuring function is well acceptable. Generally, it is concluded that both the 5TE sensor and the EC-5 sensor are suitable for WSN applications. Besides, this paper also suggested that temperature, electric conductivity and pH effects have to be compensated using appropriate correction functions respectively and various compensation models were provided accordingly.