Evaluation of the soil water content of two managed ecosystems using cosmic‐ray neutron sensing on China's Loess Plateau

Abstract

AbstractCosmic‐ray neutron sensing (CRNS) is a promising method for the continuous monitoring of soil water content (θv) at the hectometre scale. However, few studies have validated its applicability within the complex terrains of various ecosystems in semiarid loess regions. In this study, CRNS‐based θv was measured on China's Loess Plateau under two managed ecosystems (Caragana korshinskii K. shrubland [KOS] and Medicago sativa L. grassland [SAG]). The accuracy of CRNS measurement was assessed with the traditional oven‐drying method, while its sensitivity to θv variation during the study period was compared with typical point‐scale monitoring sensors (EC‐5, Decagon Devices, Inc.). CRNS was found to be strongly correlated with the oven‐drying based θv under both ecosystems, with coefficients of determination (R2) of 0.99 and 0.93, and root mean square errors of 0.006 and 0.007 cm3/cm3, for KOS and SAG, respectively. The mean monitoring radius of the CRNS was approximately 204 and 231 m for KOS and SAG, with a mean measurement depth of approximately 39 and 45 cm, respectively. Moreover, the θv determined by the CRNS and EC‐5 sensors exhibited similar trends during the observation period, excluding that for April. However, the CRNS‐based θv had a higher spatial representation for both managed ecosystems compared with that for EC‐5. No significant difference was detected in the response range of θv to precipitation between the CRNS and EC‐5 sensors at a depth of 0–10 cm, whereas the response time of CRNS for KOS was much shorter than that of EC‐5 sensors (p < 0.01). Overall, the CRNS measured hectometre‐scale θv had acceptable accuracy and sensitively traced the precipitation response under different ecosystems with high θv heterogeneity in the semiarid loess regions.Highlights CRNS accurately estimates hectometre‐scale θv in ecosystems with complex terrains. The CRNS monitoring radius is ~218 m with ~42 cm measurement depth in the loess region. The θv in the managed shrubland is higher than that of the managed grassland. CRNS has a higher sensitivity in response to precipitation than EC‐5 sensors.