『Abstract
Rice is one of the most important staple foods in the world.
Lowland paddy fields are well known for functioning as denitrification
areas, but few studies have been conducted of paddy fields situated
on hill slopes (terraced paddy fields). These terraced paddy fields
have a characteristic artificial stepped shape, and this unique
shape and periodic ponding from rice production may configure
unique hydrological properties that might be different from lowland
paddy fields. The shape and hydrological properties may also affect
transport of nutrients such as nitrogen.
This study is particularly focused on the denitrification rate
in terraced paddy fields. To understand the hydrological properties
of terraced paddy fields, a detailed water budget including the
subsurface flow components was calculated. Combining the water
budget components and chemical measurements of surface and subsurface
water, a nitrogen budget was calculated. The results showed that
about 10% of the total nitrogen input, mainly from fertilizers,
was lost, suggesting the occurrence of denitrification in the
area. The average denitrification rate of the study site was estimated
at about 0.53-0.67 g N m-2 year-1.Spatial
variations in the measured groundwater nitrate concentration suggest
that denitrification is important in both the plough layer and
the sloping area. The denitrification rate in the sloping area
was estimated at 0.67-0.78 g N m-2 year-1,
which is slightly higher than the estimates of denitrification
rate in paddy lots, i.e., 0.56-0.61 g N m-2 year-1.
The result indicates the importance of sloping areas for denitrification
in terraced paddy fields.
Keywords: Terraced paddy; Wetland; Subsurface flow; Slope; Denitrification
rate』
1. Introduction
2. Materials and methods
2.1. Study site
2.2. Observations
2.3. Geological setting
2.4. Nitrogen and nitrate budget calculation
3. Results and discussion
3.1. Characteristics of subsurface water flow
3.2. Water budget
3.3. General characteristics of chemical components and nitrogen
behavior
3.4. Estimate of denitrification rate by nitrogen and nitrate
budget
4. Conclusions
Acknowledgments
Appendix A
References