In this paper, authors proposed "Area Den-sity of Soil" （ADoS） which was a new concept for soil structure. ADoS was defined as weight of the solid phase per unit area. In addition, authors investigated how to measure ADoS by using Soft X‒ray Digital Ra-diography （SXDR）. Increase of specimen thickness and dry bulk density increased gray level of pixels in soft X‒ray digital image. Increase of ADoS also in-creased average of gray level of pixels in the image. The approximate expression to estimate ADoS from average of gray level of pixels in the image was a lin-ear function. The values calculated by the function were fit in ones measured. This fact provided us a measuring technique of ADoS by using SXDR.
The proper estimates of evapotranspiration （ET）are critical for better animal manure and/or wa-ter management practices in farmlands. Micrometeo-rological methods, e.g., the Bowen ratio method and the eddy covariance method, to estimate ET have been popularly used. Those methods, however, require specially‒designed instruments or the multiple num-bers of instruments. Estimates of ET based on the en-ergy balance at the canopy surface, on the other hand, need only routine weather data that were easily avail-able. Evapotranspiration estimated by the energy bal-ance method along with routinely‒obtained weather data was evaluated by comparing with estimates of ET by the Bowen ratio method. Weather data, i.e. shortwave irradiance, Rs（W m‒2），air temperature, Ta（K），relative humidity, and wind speed, required for the energy balance method were measured in a reed canarygrass field located near Morioka in north‒east-ern Japan. A Bowen ratio system was installed along-side in the same grass field. An energy balance on a grass canopy is expressed as a function of canopy sur-face temperature, Ts（K）．Using the Newton‒Raphson method, the energy balance equation was numerically solved for Ts , to obtain an evapotranspiration rate, E （kg m‒2 s‒1）．Values of net irradiance, Rn（W m‒2）and latent heat flux, LE （W m‒2），were overly estimated with the energy balance method when Rn>500W m‒2. For Rn<500W m‒2, however, Rn, LE, and sensible heat flux, H（W m‒2），estimated with the energy balance method agreed well with those estimated with the Bowen ratio method. Daily ETs between July 1 and 28, 2003 were calculated by accumulating E between sunrise and sunset. The daily ET values obtained by the two methods agreed very well with the correlation coefficient, r = 0.96（P<0.001）．The energy balance method to estimate daily ET could be promising.
In this research we
observed CO2 flux, soil temperature, and soil moisture in the broadleaf forest in the northern area of Okinawa in order to identify the variance of CO2 flux by observation point and day. We then compared the results with the values report-ed in previous studies. We also analyzed the particle distribution, organic matter content, and root content of gathered soils, and analyzed the relationship be-tween these data and CO2 flux. Moreover, we conduct-ed indoor experiments of CO2 flux and compared the results with those of the field observations. As a result, the following were recognized. （1） The observed CO2 flux differed by observation point. It was suggested that because diff erences in soil temperature among ob-servation points were small, its affect on CO2 flux fig-ures were minimal. （2） The observed CO2 flux was smaller than these data reported in old studies due to the removal of A0 layers. （3） The increase in soil moisture is considered to have reduced CO2 flux. （4） Relationships between CO2 flux and particle distribu-tion, organic matter content, and root content were not clear. （5） Soil temperature dependence of CO2 flux
was confirmed and Q10 values were within the range of values reported in previous studies.