Denitrification in soil and groundwater sys-tems forms the largest black box in the global nitrogen cycle, functioning as the largest sink of nitrogen with highest uncertainty. Quantification and modeling of in situ denitrification in soil and groundwater systems under various environmental conditions are needed for obtaining more reliable estimates of denitrification. This paper reviews the characteristics and controlling factors of denitrification in paddy fields and shallow aquifers, and the needs of soil physics‒based approach for quantifying and modeling in situ denitrification. Di-rect measurement of in situ denitrification under field conditions is very difficult; alternatively, nitrate remov-al rate is often measured. In paddy fields, nitrate re-moval data have been accumulated under various en-vironmental conditions, and practical modeling of nitrate removal has been going on. On the contrary, in shallow aquifers, nitrate removal is merely measured based on the determination of three-dimensional groundwater flow and nitrate transport. Soil physics should play much more significant role in determining and modeling in situ denitrification rate in soil and groundwater systems, and in elucidating the global ni-trogen cycle.
To clarify the adsorption characteristics of surfactants, it is important to understand the surfac-tant behavior in the soil and water environments. However, there are few adsorption studies for highly humic soil. In this study, the adsorption characteristics of dodecylbenzene sulfonates in a highly humic soil were investigated. A non‒allophanic Andisol was used since this soil contains a large amount of humic sub-stances and is only negatively charged. Thus, electri-cally, only repulsive force is generated between the soil and the surfactant. The adsorption amount was measured using the batch method at an electrolyte concentration of 100 mmol L－1 NaCl in order to shield the electric field near the soil particle surface and em-phasize hydrophobic reactions. The adsorption iso-therm was examined using the Langmuir‒Freundlich‒Hill equation. The adsorbed amount increased sharply with increasing concentrations in the low‒concentra-tion range. The sharp increase indicated cooperative adsorption caused by hydrophobic interaction among the carbon chains of adsorbing surfactants. The ad-sorption amount became higher at a lower pH because electrostatic repulsion between the soil and the surfac-tant decreased. The adsorption of dodecylbenzene sul-fonate with a linear carbon chain was larger than that with a branched chain due to the difference of the car-bon chain structure.
A low cost unified system for relative gas diffusivity（Dp/D0）and air permeability（ka） measure-ments has been developed. Instead of the conventional sliding‒mechanism, plastic films’ shutter has been pro-posed for the Dp /D0 measurement. While for the ka measurement, a method has been introduced by utiliz-ing the principle of Mariotte’s bottle and manometers instead of much costing air pump, mass flow meter, and pressure sensor/gauge. The measured Dp/D0 and ka of Toyoura sand were in a good agreement with those obtained in the literature, and the proposed method enabled to lower the apparatus cost up to 40 % of the common method cost.