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DIVISION S-5—PEDOLOGY

Drainage Network Analysis for Regional Partitions of Alluvial Paddy-Field Soils

^a Department of Agricultural Engineering, Faculty of Agriculture, Kagawa University, Ikenobe 2393, Miki, Kagawa, 761-0795 Japan
^b Department of Agronomy, Faculty of Agriculture, Yamagata University, Tsuraoka, Yamagata, 997-8555 Japan

* Corresponding author (ishida{at}ag.kagawa-u.ac.jp)

Terrain data on floodplains might be a useful source of ancillary information about soil properties at a regional scale. However, terrain data are not believed to be suitable for obtaining information on paddy-field soils on floodplains, because the contrast in the topography of floodplains is only slight. This study was conducted in the Tsuruoka area, a part of the Shonai Plain in the northern part of Japan, to evaluate whether a division of floodplain into landform elements can provide useful information on delineation of paddy-field soils. As source data for the division, a digital elevation model (DEM) was constructed based on a closely spaced differential global positioning system (DGPS) survey and geostatistical interpolation. By using the DEM, drainage network analysis was performed to delineate the landform units. To evaluate correspondence of soil classification with the land division, soil chemical data from 154 soil samples were classified by using a set of numerical procedures. The numerical procedures included principal component analysis and unsupervised classification techniques. In the land partition map created, each landform unit could satisfactorily represent a separate soil group as characterized by soil chemical properties. A statistical analysis revealed that the regional partition map was better than the conventional soil map inasmuch as the partition map described more satisfactorily the spatial distribution of soil chemical properties. However, this conclusion depends largely on the spatial resolution and precision of the DEM. The useful regional partition map could not be produced by different DEM that has lower resolution and accuracy.

Abbreviations: AIC, Akaike's Information Criteria • BSP, base saturation percentage • CEC, cation-exchange capacity • EXCH, exchangeable • DEM, digital elevation model • DGPS, differential global positioning system • GPS, global positioning system • PAC, Phosphate Adsorption coefficient • TN, total N