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 land form 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 land-form 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 land form 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 inas-much 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.