Performance of a non‐nuclear resonant frequency capacitance probe. III. error analysis

Abstract

All techniques used to measure soil water content have errors associated with them. These errors are further propagated when soil volumetric water contents are numerically integrated over a number of depth intervals to estimate the soil water storage for the entire profile. Previous studies had field‐tested the performance of a commercial capacitance probe (Troxler Sentry 200‐AP). The probe was calibrated and the measured data on crop water use were compared with that reported previously in literature using other instruments. However, the errors associated with the field estimates of soil water storage and crop water use measured with the Sentry 200‐AP capacitance probe were not evaluated. The objective of this study was to analyze these associated errors. Equations were derived to evaluate the errors incurred in calculating the volumetric water content using the fitted field calibration curve for the Sentry 200‐AP capacitance probe and in the estimates of the crop water use. This study suggests that the error in making in situ measurements of soil water content in heterogeneous soil systems using the Sentry 200‐AP capacitance probe depends on the degree of saturation at the point of measurement in the soil profile. The Sentry 200‐AP capacitance probe produces errors of >5% in measuring soil volumetric water contents of >35% in heterogeneous soil systems.