Estimation of Soil Moisture in the Shallow Root Zone in a Humid Region

抄録

Air temperature, sunshine duration and precipitation are used to estimate the soil moisture in the shallow root zone. The model for the estimation of the soil moisture is based on the water balance of the root zone. The daily amount of evapotranspiration was estimated using the Priestley and Taylor model, modified by the ratio of total soil moisture and soil moisture at the field capacity in a given soil layer. The upward capillary flow was evaluated from the unsaturated hydraulic conductivity of soil and the gradient of water potential between the center of the root zone and at a depth 100cm from the center. This model was used to estimate the soil moisture in the 40cm deep root zone from surface in the Abashiri district in Hokkaido, Japan.
Estimated soil moisture was in agreement with the measured soil moisture by tensiometer in the range of PF 1.8 to PF 2.8. The amount of upward capillary flow was higher than the expected values. Therefore, we concluded that the soil moisture could not be estimated precisely without the estimation of the upward capillary flow.