SPATIAL VARIABILITY IN THE UPPER SOIL LAYER OF A NO-TILL FIELD USING A SMALL-SCALE DYE EXPERIMENT.

Small-scale (33 cm by 33 cm) dye experiments were performed to evaluate the spatial variation of infiltration by evaluating dye distribution within the upper 10-cm soil depth of a well-established no-till corn field. The variation of infiltration was estimated by measuring the dye concentrations in the soil samples obtained from the 0- to 3-cm, 3- to 6-cm, and 6- to 10-cm depths of the infiltration test volume (10,890 cm3). Contour maps of dye concentrations were prepared for each soil layer and used to estimate the percentage of the infiltration area that had a higher than average dye concentrations. Results indicate that (1) statistically, the dye concentration in the upper soil layers (0 to 3 cm) have a higher average dye concentration with less variability than the middle and lower soil layers; (2) the majority of the infiltration solution appeared to pass through 23% of the infiltration area; and (3) the spatial distribution of the dye concentrations are highly heterogeneous. The statistically and spatially heterogeneous dye distribution suggests that under ponded infiltration conditions in no-till systems, preferential flow may be the primary mechanism affecting the distribution of infiltrating water throughout the 0- to 10-cm depth. The heterogeneous dye distribution suggests preferential flow was established in the 0- to 3-cm layer for most of the tests.