Abstract
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.
