Using Capacitance Sensors for the Continuous Measurement of the Water Content in the Litter Layer of Forest Soil

Abstract

Little is known about the wetting and drying processes of the litter layer (Llayer), likely because of technical difficulties inherent in nondestructive water content (WC) monitoring. We developed a method for continuously measuring the WC of leaf litter (the “LWC method”)in situusing capacitance sensors. To test variants of this approach, five (for the LWC_5) or ten (for the LWC_10 method)Quercus serrataleaves were attached around capacitance sensors. The output voltage used for each LWC method was linearly correlated with the gravimetric WC (LWC_5:R2=0.940; LWC_10:R2=0.942), producing different slopes for each calibration line. Forin situcontinuous measurements of WC in theLlayer, two sensors were used, one placed on top of theLlayer and the other at the boundary between theLand mineral layers. The average continuous WC of theLlayer was then calculated from the output voltage of the two sensors and the calibration function, and this value was linearly correlated with the gravimetric WC(R2=0.697). However, because theLlayer characteristics (e.g., thickness, water-holding capacity, and species composition) may differ among study sites, appropriate approaches for measuring this layer’s moisture properties may be needed.