The hydraulic function of three types of macropores during saturated flow through four swelling fine clayey and very fine clayey soil horizons was characterized with methylene blue as a tracer, and was quantified in large thin sections with the Quantimet 720. All three types of macropores, described as channels, vughs, and planar voids, contributed to flow. Distinction between “smooth” and “rough” ped faces in field structure descriptions proved meaningful for three soils with high linear extensibility values, because vertical flow did not occur along interconnected planar voids adjacent to “smooth” peds, whereas it did occur along “rough” peds. However, flow did occur along “smooth” ped faces in the fourth soil, which had significantly lower extensibility values. Calculations of hydraulic conductivity Ksat, based on the observed dye patterns, are difficult because the dye solution flowed in interrupted patterns along the walls of the macropores without apparently filling them, due to the occurrence of smaller pore “necks” in overlying soil. But the number and percentages of colored pores for each of the three macropore‐types showed (with one exception for planar voids) consistant differences among the four soils, which corresponded with differences in measured Ksat values.
Infiltration into dry cracked clay soil was simulated by combining two existing physical simulation models for vertical and horizontal infiltration, using boundary conditions for horizontal infiltration that were defined by morphological data. Vertical flow into the cracks occurred when the application rate exceeded the calculated vertical infiltration rate of peds between cracks. Calculated horizontal infiltration from the cracks into adjacent dry peds was limited because it had to occur from a few small vertical bands along which the water moved. The contact area (S) of all bands had been determined in situ in 0.5‐m2 plots per 10‐cm depth interval using morphological staining techniques. S was a function of the applied flow regime. “Short‐circuiting,” which was defined as preferential movement of free water along large pores through unsaturated soil, was predicted well by the model. Short‐circuiting increased when the initial moisture content of the soil was higher.
A method of calculating Ksat in pedal soil materials on the basis of morphometric data yielded reproducible results for seven soil peels sampled in the argillic horizon of a Batavia silt loam. Calculated values were reasonably close to those measured in situ with the double tube method. The method was also successfully applied to impregnated horizontal sections through soil cores. Dye studies demonstrated the validity of some of the underlying assumptions of the method, which predicts a strong relationship between core height and measured hydraulic conductivity in pedal soil materials. Experiments confirmed this relationship and a representative core size was defined for the studied horizon using the morphometric data.
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