Near-surface Soil Moisture Observation in a Heavy Clay by Measuring Cosmic-ray Neutrons

Abstract

We employed the COsmic-ray Soil Moisture Observing System (COSMOS) to monitor temporal changes in epithermal neutron count in reclaimed farmland characterized by high levels of clay deposits. The number of epithermal neutrons was corrected for atmospheric pressure, absolute humidity, and background neutron count hourly. The corrected hourly count of epithermal neutrons (N) showed substantial variability and no discernible correlation with the volumetric water content (θ) measured by time-domain transmission (TDT) sensors at three different depths (5 cm, 15 cm, and 25 cm) in proximity to COSMOS. However, the daily mean of N exhibited a clear negative association with θ at a depth of 5 cm. These findings suggest that COSMOS can effectively monitor changes in mean θ in surface soils of reclaimed agricultural land with high levels of clay and a tendency to retain high soil moisture conditions.