MACROPOROSITY AND INITIAL MOISTURE EFFECTS ON INFILTRATION RATES IN VERTISOLS AND VERTIC INTERGRADES

In Vertisols and vertic intergrades, spatial and temporal variability remains a challenge in water flow and chemical transport studies, Infi ltration measurements were made with tension infiltrometers operating at supply potentials greater than or equal to -0.24 m in 42 clay-textu red horizons from seven Vertisols and three vertic Alfisols, Variabili ty of near saturated infiltration was shown to be linked closely to so il macroporosity and moisture, Data revealed negatively sloped relatio nships when soil macroporosities were plotted against initial gravimet ric soil water contents and when apparent steady-state infiltration ra tes were plotted against initial water contents, A positive linear rel ationship was observed between apparent steady-state infiltration rate at Om supply potential and soil macroporosity, Because of well develo ped structure and the occurrence of various types of macropores, most of the vertic soils had enhanced low-tension infiltration rates compar ed with less structured clay soils, The change in soil macroporosity i n the shrink-swell clay soils when change in water content occurred ha d a greater impact on low-tension flow processes than the change in wa ter content itself, Soil cracking, aggregation, biopores, and the time scale involved in shrink-swell processes were important factors that provided a physical understanding of infiltration behavior in the fiel d.