Water Infiltration and Redistribution in a Silt Loam Subsoil with Vertical Worm Channels

Abstract

Infiltration and redistribution of water in a fine silty, mixed, mesic Fluventic Eutrochrept with macropores (dominantly vertical worm channels) were studied with physical and morphological techniques. Infiltration rates in individual worm channels were measured and channel morphology was studied by excavation after adding methylene blue and gypsum. Three different steady infiltration rates corresponded with different channel morphology. One channel occurred per 200 cm2 of soil. The measured, dominant infiltration rate in a channel was used to calculate ponding time on and the associated water movement in the soil matrix after adding 2 cm of water. The latter was calculated with an existing simulation model for one‐dimensional infiltration in homogeneous soil using K‐θ and h‐θ data. Calculations of h indicated lack of soil saturation. This agreed only with in‐situ measurements when small tensiometer cups were used. Large cups intercepted water‐conducting macropores, erroneously suggesting saturation of the entire soil matrix. Addition of a 5‐cm thick layer of sand to the surface of infiltration made the macropores discontinuous and induced saturated conditions, as measured and simulated. Measurement of infiltration rates into individual macropores, rather than calculation of those rates, is recommended when macropore morphology is irregular.

Quantifying the Effects of Earthworms on Soil Aggregation and Porosity

“…These replicas can be made using materials such as molten lead (Teotia et al 1950), plaster (Bouma et al 1982;Wang et al 1994), wax (Smettem 1986), or fiberglass resin (Shipitalo and Butt 1999;Shipitalo and Gibbs 2000). Like excavation, this technique is not always successful because of an inability to fill the burrows completely with the impregnating media.…”

Temporal variability of subsurface stormflow formation

“…Beven and Germann (1982) pointed to the relation between antecedent soil moisture and preferential infiltration in that "higher initial soil moisture content in the soil may also allow deeper penetration along the macropores by reducing the lateral losses". Similarly, Bouma et al (1982) named soil water content as a crucial parameter for the "magnitude of bypass flow". Experimental evidence for this hypothesis comes from Weiler (2001), who observed reduced flow from macropores into the soil matrix, when the soil was wetted before the experiment.…”

A novel method for measurement and characterization of soil macroporosity

“…Attempts to quantify and characterize macropores have involved the implementation of one or more physical or morphological methods. Physical methods employ breakthrough curves (3,5), hydraulic conductivity measurements (11), and/or tensiometers (12) as indirect indicators of macroporosity. The morphological approach, on the other hand, evaluates the actual number, size, area distribution and continuity of macropores under natural conditions (13).…”

“…Most of these methods employ the use of thin section analysis (12,14), soil profile photography (15,16), or dye tracers (13,17) to define the macropore area of interest. Then, the size, shape, and configuration of pores are quantified using an image analysis system (14) or manual measurements (12). Although the image analysis system is a preferred method for these types of determinations, the high cost associated with this equipment and degree of expertise needed to operate the unit may not justify its use as a general analytical tool.…”