Litter layer, which is an important source of soil respiration (SR), is exposed to large fluctuation of temperature and water content (WC). To understand SR variations in forests, the litter layer should be considered as an individual compartment. In addition, continuous monitoring of the temperature and WC of litter with fine temporal scale is needed. However, it is difficult to continuously measure WC of the litter in the field because of the litter porosity. Half-bridge (HB) sensor, which measures electronic conductance as index of litter WC, is one of the valuable methods to measure WC of litter.

In this study, we examined applicability of HB sensor for five litter types, and tried to find out adequate indicators instead of the actual litter to avoid the litter damage. Applicability of HB sensor and adequacy of the indicators were assessed by confirming the correlation between sensors outputs and actual litter WC, and the calibration lines are obtained.

Our results demonstrated that sensors outputs correlated to the litter WC for every litter types, and calibration lines are different from each other. It was probably caused by differences of shapes and water holding capacity of each litter types. We also found out the indicators with low water holding capacity are inadequate for measuring lower litter WC because the indicators dry faster than litter.