|Mcintosh, Gordon - UNIVERSITY OF MINNESOTA|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: January 5, 2001
Publication Date: N/A
Technical Abstract: Macropores created by biological or physical processes can profoundly influence water movement through the soil. In cold regions, macropores are subject to wetting/drying and freezing/thawing. Little is known, however, concerning the stability of macropores during winter. This study investigated changes in the physical dimensions of macropores from autumn to spring in the northern US Corn Belt. Artificial macropores were constructed in the fall at a field site that was in fallow the previous year. Stainless steel tubing (wall thickness 0.9 mm) was used to extract 5, 10, and 15 mm diameter soil cores. The artificial macropores created with the tubing were 300 mm deep. Macropores were evenly spaced at a distance of 100 mm over a 1 m**-2 area. Pore size treatments were replicated thrice. Neutron access tubes and Time Domain Reflectometry (TDR) probes were installed in each plot to monitor total and liquid soil water content. In the fall and spring, castings of 5 pores per plot were made using dental plaster on the 5 mm pores and molten paraffin wax on the 10 and 15 mm pores. These castings were excavated to determine length, diameter, and volume of pores. In the fall, dry soils and high winds resulted in surface creep and saltation of soil particles, thereby filling pores. Approximately 50 and 10% of the 5 and 10 mm pores, respectively, had filled with soil prior to freeze-up in the fall. After snowmelt in the spring, all 5 mm pores were filled with soil. The walls of the larger pores were rougher in the spring than fall, suggesting degradation of the wall during winter. This study suggests that macropores are not stable during winter, but are subject to change as a result of dry soil deposition or slaking of walls. These changes will likely impact water movement through soil.