Peat wetlands are considered to be the major sources of greenhouse gases. Many studies have been con-ducted to evaluate quantitatively greenhouse gases produc-tion and consumption in peat soils, however, only limited information on dynamics of greenhouse gases in peatland forest soils. In this study, emission, production, and con-sumption of greenhouse gases such as CO2, CH4, and N2O were investigated at a soil profile in the peatland forest by combining techniques of a closed-chamber method, annual monitoring of soil gas concentrations in the unsaturated zone, and laboratory measurements on water retention and gas diffusivity for soil core samples. Results show that the annual amounts of 725 g CO2-C m−2 were emitted from the soil surface and approximately 90% of the CO2 was produced at the depth interval less than 10 cm. On the other hand, the soil profile acted as a CH4 sink and the annual amounts of 0.47 g CH4-C m−2 were oxidized （consumed) within the 0–10 cm depth interval. For the dynamics of N2O, the annual amounts of 0.249 g N2O-N m−2 were emitted from the surface and both production and consumption occurred at each depth interval above the water table. Especially, the production and consumption of N2O was significant at the 22-cm depth from the surface. It was also revealed that the N2O was produced / consumed markedly even during the snowfall and snowmelt periods differing from the CO2 and CH4.
An experiment was conducted in a vinyl house at Gifu University, Japan, from June to November 2007 to evaluate the potentialities of the three soil types under various water deficit conditions to yield of soybean. The soil type was the first factor with three different soil types, comprising of clay loam, sandy clay loam, and sandy loam soils, classified as Inceptisol, Ultisol, and Andisol, respec-tively. Water deficit (D) was the second factor with four levels including D1 (0 – 25 %), D2 (25 – 50 %), D3 (50 – 75 %) and D4 (75 – 100 %) water deficits of total available water (TAW). The crop water requirement (CWR) of soybean in the three soil types significantly decreased with the increas-ing water deficit levels, and the highest was in Incepti-sol, followed by Ultisol and then Andisol under all wa-ter deficit levels. Grain yield of soybean per unit area in Inceptisol was the highest, followed by Ultisol and then Andisol under all water deficit levels. The values of yield efficiency (YE), indicating the grain yield per unit CWR, was strongly influenced by water deficit level, and the max-imum YE occurred at the water deficit level D3 (50 – 75 %) in all the three soil types. However, there were no signif-icant differences at 5 % level among the maximum values of YE in the three soil types. The lowest yield response factor (Ky), indicating the relative yield loss to relative wa-ter deficit, was seen in Inceptisol (Ky = 0.42), followed by Ultisol (Ky = 0.64) and then Andisol (Ky = 0.87) under the water stress lower than 50 – 75 % of TAW. These results indicate that deficit irrigation in Inceptisol contained the finest soil texture is the most effective for economic water usage among the three soil types under the water deficit lower than 50 – 75 % of TAW (D3).
This study investigated the effect of local wa-ter flow around the constantan (Co) line of a sensor caused by heating the line on the measured convective velocity of ponded water in a paddy field. Then, a method of cali-brating the sensor, considering this effect, was examined. The output voltages of the sensor at a water temperature of 20◦C were 6 % larger than those at 30◦C when the en-ergy supplied to the Co line was 0.52 W m−2, indicating that an increase in water temperature accelerated the local water flow. Based on this, a method of calibrating the sen-sor while supplying the Co line with 0.13 W m−2 energy was developed. This calibration, which was expressed by a linear function, had a significant correlation (r2 = 0.97) between the sensor output and convective velocities in the 0.0 to 1.25 mm s−1 range.
In order to simulate the behavior of NO3 in the agricultural land, it is necessary to obtain the information of the relationship between solute concentrations of pore water and adsorbed solute amount, which are described as the adsorption isotherm (AI) lines at six depths. However, the parameters list of the AIs, which depend on soil type, has not yet been provided with all as inventory data. There-fore, it is necessary to provide with all parameter list as in-ventory data immediately. For the purpose of collection in substantial inventory data of AIs of NH+4 and NO−3, as the first step, the authors conducted the adsorption experiment of Andosol and Gray lowland soil at the arbitrary depth. As a result, the AI lines in all soil type except for Andosol (30 cm depth of upland field) could be expressed as Langmuir type AI. In the Andosol (upland field), maximum adsorp-tion NH+4 tended to decrease with depth except for z = 50 cm, while adsorbed NO−3 was strongly dependent on depth and its maximum adsorption tended to increase with depth.