Validation of Wireless Volumetric Soil Water Content Sensor Based on Soil Temperature and Impedance Measurements

Abstract

The rational use of water resources requires accurate assessment of soil moisture content. During the last three decades, electromagnetic measurement techniques have evolved into versatile, cost- effective solutions for conducting in situ soil moisture measurements. However, it is still necessary to further continue developing technological solutions that can yield soil moisture measurements close to the real content, stressing ease of use and can be adjusted to operate under different site conditions. Here the authors describe a volumetric soil moisture measurement instrument based on soil impedance measurements. The soil temperature is used as an additional parameter to implement a measurement compensation method. The measurement compensation process uses a feedforward artificial neural network. 10 measurements were obtained in situ in three test fields (maize, wheat, pastureland), over a period of 10 weeks (october-december 2017). The results were compared to measurements obtained using a commercial soil moisture instrument (6050X1 Trase System) and the gravimetic method. The results indicate that the prototype developed for this application can yield information close to gravimetric data for the three test sites (Maize SSE [sum of squared error]: 5.97, Wheat SSE: 19.81, Pastureland SSE: 12.71) in agreement with TDR data.nbs