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Preferential Flow Patterns in Paddy Fields Using a Dye Tracer

Institute of Soil Landscape Research, Leibniz-Centre for Agricultural Landscape Research (ZALF), Eberswalder Strasse 84, D-15374 Müncheberg, Germany

View larger version (22K): [in this window] [in a new window]   Fig. 1. Soil water pressure head as a function of time (mean values and standard deviation of three replicates) measured using insertion tensiometers at six depths. Black arrows mark the dye tracer application times. Precipitation (P) is in millimeters per day.

View larger version (54K): [in this window] [in a new window]   Fig. 2. Schematics of creation of profiles: vertical profiles were created toward the center of the plot first, horizontal profiles followed afterward. Examples show vertical face at the center, (left) horizontal face at 20-cm depth for Plot 2b, and (right) all horizontal profiles created for Plot 2a.

View larger version (108K): [in this window] [in a new window]   Fig. 3. Examples of horizontal profiles: stained surface cracks at 4- and 5-cm depths, more horizontally extended dye pattern at 10-, 12-, and 15-cm depths, stained cracks and biopores at 17- to 30-cm depths, and more horizontally extended dye pattern below 40-cm depth.

View larger version (79K): [in this window] [in a new window]   Fig. 4. Example of staining patterns: upper left corner (0.5 by 0.5 m, 0–50-cm depth) of a vertical profile at 10-cm horizontal distance from the center of Plot 2b. Arrows indicate the plow pan at about 15-cm depth and a second soil structural change at about 40-cm depth.

View larger version (28K): [in this window] [in a new window]   Fig. 5. Binary images of horizontal staining pattern for (top) Plot 2a and (bottom) Plot 2b (left) in the cracked cultivated topsoil, (center) in the compacted plow pan with cracks and biopores, and (right) in the uncompacted subsoil with radially spread dye around macropores.

View larger version (44K): [in this window] [in a new window]   Fig. 6. Spatial distribution of (left) superimposed two-dimensional vertical cross-sections and (right) horizontally integrated one-dimensional vertical values of relative dye coverage vs. depth for (top) Plot 1b, (center) Plot 2a, and (bottom) Plot 2b. Solid lines indicate values obtained from vertical profiles, crosses indicate values obtained from horizontal profiles. The grey-scale bar (Plot 2a, center) for the dye coverage ranges between values of 0 (white) and 1 (black), indicating the relative numbers of stained pixels from all vertical two-dimensional cross-sections. Arrows indicate peaks of dye coverage.

View larger version (61K): [in this window] [in a new window]   Fig. 7. Horizontal views of the plots showing the soil surface topography (lowest locations are blue and highest locations are red-brown). Location of cracks (black lines) and rice stubbles (black solid circles) were obtained from photos. For Plot 1b, cracks and stubbles are not shown for half the plot since photos from the soil surface above the vertical profiles were not available.

View larger version (31K): [in this window] [in a new window]   Fig. 8. Topography of the surface of the plow pan, determined at a separate 1-m2 plot in Field 2. The lowest spot was used as the reference height.

View larger version (101K): [in this window] [in a new window]   Fig. 9. Example of (right) stained structures with little lateral dispersion close to (left) stains with strongly laterally dispersed dye at one horizontal profile of Plot 2a at 40-cm depth.